Academic literature on the topic 'Clarias gariepinus Fish culture'

AbstractCannibalism is an important characteristic of African catfish that significantly reduces the number of stocked fish at harvest. This study evaluates the effect of reciprocal hybridization of Clarias batrachus and Clarias gariepinus on cannibalism and growth performance of their progenies in an indoor rearing system. The result obtained reveals excellent performance of hybrids of C. gariepinus ♂ and C. batrachus ♀ over the purebreds in terms of growth. However, the reciprocal hybrids between C. gariepinus ♀ and C. batrachus ♂ all died few hours after hatching. Cannibalism was significantly reduced in the crosses between C. gariepinus ♂ and C. batrachus ♀ with 100% survival after five months of culture. Hence, this could be exploited in commercial production of catfish to reduce cannibalism and increase harvest size of fish farmers.

Growth of African catfish (Clarias garipinus) is characterized by large size heterogeneity resulting in poor growth performance and cannibalism. Strategies that limit size heterogeneity in C. gariepinus culture are therefore advocated. This study determined the effects of grading frequency on the growth performance and cannibalism of C. gariepinus in tank culture system. Three treatments designated as G0 (no grading), G2 (grading every 2 weeks) and G4 (grading every four weeks) in a Completely Randomized Design (CRD) was applied in triplicate. The tanks were stocked with 200 fingerlings each. Sampling was conducted weekly to measure length and weight of fish. Mortalities were recorded and dead fish observed under dissecting microscope to ascertain that it is due to cannibalism. Growth performance in terms of final mean weight, weight gain, specific growth rate and food conversion ratio were significantly (P < 0.05) affected by frequency of fish grading. The C. gariepinus graded every two weeks grew better than those graded every four weeks and were all above the no grading treatment. Significant changes in fish heterogeneity were observed after day 42. The size variation was significantly affected by grading frequency. The mean TL of fish graded every 2 weeks was the highest, followed by grading every four weeks and finally the no grading treatment was the lowest. Fish size heterogeneity (CV% and skewness) was consistently the highest in C. gariepinus in no grading treatment followed by fish where grading was done every four weeks while it was lowest in treatment where feeding was done every two weeks. Mortality owing to cannibalism was affected by grading frequency where highest cannibalism mortality occurred in C. gariepinus where there was no grading followed by grading every four weeks and intermediate at grading frequency every four weeks. Meanwhile other mortality by other causes such as such as wounds and suffocation in fish did not differ with grading frequency. Keywords: Cannibalism, Coefficient of variation, Fish grading, Fish growth, Growth heterogeneity

This study was carried out to determine the fatty acid composition and sensory quality of Clarias gariepinus from different culture enclosures (plastic, sandcrete tanks and earthen ponds), at the Teaching and Research Farm of Department of Fisheries and Aquaculture Technology, Federal University of Technology, Akure, Ondo State, Nigeria. The comparative work was carried out to find out if habitat could influence the nutrient composition of the fish. Standard procedures were used in the analysis of tissue nutrient. Sensory evaluation study revealed differences in taste and texture indices considered for C. gariepinus reared in plastic, sandcrete tanks and earthen ponds (p<0.05). Fatty acid profiles of C. gariepinus were determined using Gas chromatography-mass spectrometry (GC-MS) method. The percentage of saturated and unsaturated fatty acids was higher (49.99%, 23.17%) in earthen pond cultured C. gariepinus than the plastic and sandcrete tanks. The study revealed that C. gariepinus raised in earthen pond possess fatty acid composition and sensory quality advantages over the plastic and sandcrete tanks. Keywords: Fatty acids, Sensory evaluation, Culture enclosures, Clarias gariepinus

Abstract This study determined the genetic variations that exist in Clarias gariepinus obtained from two natural populations in Nigeria, using their serum protein profiles. A total of 51 samples of Clarias gariepinus collected from Ado-Ekiti and Ilesa were used for this experiment. Blood was extracted from the caudal vein of each individual fish and electrophoresis was performed based on standard methods. Following this, gel images were taken, scored and subjected to classical cluster analysis using Bray-Curtis similarity index. This showed the presence of variations in C. gariepinus between the studied populations and samples from Ado-Ekiti reservoir displayed more diversity than those from Ilesa. Hence, this showed the feasibility for selecting samples from Ado- Ekiti to improve culture of C. gariepinus in further breeding studies.

Wetland incorporated fish-rice farming (FRF) is a possible solution to the problem of high costs of fish feeds in aquaculture in Cameroon. For 12 weeks, at the University of the Buea (UB) the growth of the fish, Clarias gariepinus in concurrent culture with rice (Oryza sativa, L.) in two rice plots (rice plot 1 and rice plot 2stocking sites) in the University of Buea wetland and in two earthen ponds (fish pond 1 and fish pond 2stocking sites) fed compounded diet at 5% body weight was investigated. Physico-chemical water quality parameters of all the fish culture sites were monitored. Mean fish weight gain was significantly higher (P<0.01) in the wetland rice plots (329.21±44.35g) than in the two earthen ponds (30.01±2.84g). Apart from low mean dissolved oxygen values in the rice plot 1 (3.14±1.19 mg/L) and rice plot 2 (2.18±0.23 mg/L), mean values for physico-chemical water quality parameters were within recommended ranges for C. gariepinus growth in all the four culture sites. This FRF experiment proved a better practice in fish growth than the conventional earthen pond culture in Buea, Cameroon. Its adoption by local fish farmers is recommended. Keywords: Wetland integrated fish-rice farming, C gariepinus, earthen pond culture, and fishpond.

<p class="NoParagraphStyle" align="center"><strong>ABSTRACT</strong></p><p class="NoParagraphStyle" align="center"> </p><p class="NoParagraphStyle">A series of experiments was performed to analyze protein digestibility, ammonia excretion, and also heterothropic bacteria and phytoplankton dynamics in the catfish <em>Clarias gariepinus</em> culture. In the digestibility experiment, catfish with an individual initial size of 43.67±0.83 g were stocked into 120 L conical fiberglass tanks at a density of 20 fish per tank. Fish were fed on with commercial diet supplemented with Cr₂O₃ indicator at a concentration of 1%. In the ammonia excretion experiment, catfish with an individual size of 111.6±9.5 and 40.6±3.4 g, respectively, were placed into a 10 L chamber filled with 8 L of water. Total ammonia nitrogen (TAN) in the chambers were monitored every hour for six consecutive hours. In the bacteria and phytoplankton dynamics experiment, catfish were stocked in the 25 m² concrete tanks which was divided into two compartments (catfish 10 m², and heterotrof compartments 15 m²). Catfish with individual size of 42,5±0 g were stocked into the tanks at a density of 100 fish per tank. Water was recirculated from catfish compartments to heterotrophic compartments. Fish were fed with floating feed. Molasses as carbon source for heterotrophic bacteria was applied daily. The experiment was conducted for six weeks. The results showed that the protein digestibility was 61.97±7.24%. Larger fish (size of 111.6 g) excreted ammonia at a rate of 0.008±0.003 mg TAN/g fish-weight/hour, which was lower than that of the smaller catfish (size of 40.6 g), i.e. 0.012±0.004 mg TAN/g fish-weight/hour.</p><p class="NoParagraphStyle"> </p><p class="NoParagraphStyle">Keywords: protein digestibility, ammonia excretion, catfish</p><p class="NoParagraphStyle"> </p><p class="NoParagraphStyle"> </p><p class="NoParagraphStyle" align="center"><strong>ABSTRAK</strong></p><p class="NoParagraphStyle"> </p><p class="NoParagraphStyle">Serangkaian penelitian telah dilakukan untuk menganalisis ketercernaan pakan dan protein, ekskresi amonia, serta dinamika bakteri dan fitoplankton pada budidaya ikan lele (<em>Clarias gariepinus</em>). Pada penelitian ketercernaan pakan, ikan lele berukuran 43,67±0,83 g/ekor dipelihara dalam bak <em>fiberglas</em> berbentuk corong berukuran 120 L dengan kepadatan 20 ekor/bak. Ikan diberi pakan berupa pelet yang diberi indikator Cr₂O₃ sebanyak 1%. Pada penelitian ekskresi amonia, ikan lele berukuran 111,6±9,5 dan 40,6±3,4 g/ekor yang telah diberi makan sampai kenyang dimasukkan ke dalam stoples berisi 8 L air. Kadar amonia total (<em>total ammonia nitrogen</em>, TAN) di dalam stoples diukur setiap jam selama enam jam. Pada penelitian dinamika bakteri dan fitoplankton, ikan lele dipelihara pada bak beton berukuran 25 m² yang disekat menjadi dua bagian yaitu bagian ikan lele (10 m²) dan bagian heterotrof (15 m²). Ikan lele dengan bobot awal 42,5 g/ekor ditebar ke dalam bak dengan kepadatan 100 ekor/bak. Air mengalir secara resirkulasi dari bagian ikan lele ke bagian heterotrofik dengan bantuan pompa. Pakan yang diberikan berupa pelet apung komersial. Molase ditambahkan setiap hari sebagai sumber karbon untuk pertumbuhan bakteri heterotrofik. Penelitian dilaksanakan selama enam minggu. Hasil pengamatan menunjukkan bahwa ketercernaan protein dari pakan yang diuji adalah 61,97±7,24%. Ikan lele berukuran besar (111,6 g/ekor) menghasilkan amonia sebanyak 0,008±0,003 mg TAN/g ikan/jam, lebih rendah dibandingkan dengan ikan yang berukuran lebih kecil (40,6 g/ekor), yaitu 0,012±0,004 mg TAN/g ikan/jam. </p><p class="NoParagraphStyle"> </p><p>Kata kunci: ketercernaan protein, ekskresi amonia, ikan lele</p>

The study was designed to investigate the rate of larval (maggot) production from different culture enclosures, as well as to compare the cost effectiveness and utilization of the maggot in the diet of African mud catfish, Clarias gariepinus. Musca domestica larvae were cultured from poultry dung for five week, where upon they were utilized as a replacement for fish meal in the diet of fingerlings of African mud catfish. The maggots were cultured in four different enclosures: aluminium mobile maggotry, aluminium, plastic and wooden boxes. The harvested maggots were processed by oven drying and powdered as maggot meal. The maggot meal was used to substitute fish meal in eight diets with different inclusion levels of 0% (control), 20%, 30%, 40%, 50%, 60%, 70% and 80%. The formulated diets were fed to C. gariepinus fingerlings in triplicates for 10 weeks. The growth, nutrient utilization and survival of fish were monitored during the experimental period. The cost effectiveness of different culture enclosure was studied. Results indicate that aluminium box was the best option, giving the highest weight of maggot production, and was the most cost effective of all the culture enclosures studied. Significant differences (p < 0.05) were recorded in weight gain of fish between the control and the maggot meal-based diets, while the highest weight gain was observed in fish fed 70% maggot meal-based diet. Specific and relative growth rates were found to be high in fish fed 60% maggot meal diet, while they were lowest in fish fed 20% maggot meal diet and the control diet. The best protein intake was recorded in fish fed the 70% maggot meal-based diet and lowest in fish fed the control diet. Survival of fish was generally high (78.3%-93.30%) and was significantly (p < 0.05) different between the fish fed as the control and the maggot meal-based diets. The study confirms that maggots of Musca domestica are suitable as partial replacement of fishmeal at 60-70% inclusion level for optimal growth performance and nutrient utilization in Clarias gariepinus fingerlings.

The growth performance of catfish Clarias gariepinus using imported feeds and locally made feeds of the same crude protein were compared. C. gariepinus (mean weight 12.8g) juvenile were reared in cages for a period of 12 weeks on different feed. Two imported feeds (skretting and copens) were purchased and two local feeds (corresponding to treatment) were compounded to contain the same level of crude protein. Locally ingredients used are maize, fish meal, groundnut cake, soya bean meal, bone meal, lysine, methionine, premix, vegetable oil, salt but varying fish meal and soya bean meal as follows, treatment 1- (11.38% to 7.5%), treatment 2-(7.5% to 11.38%) respectively. The pelleted feeds were fed at the rate of 5% of the fish biomass. The growth response was assessed in terms of daily weight gain, relative weight gain, specific growth rate, feed conversion ratio, mortality and survival rate. The results showed that the two local feeds promoted positive growth, implying that the use of different levels fish meal and soya bean meal (11.38% and 7.5%) favoured culture of juvenile C. gariepinus.Key Words, Clarias gariepinus, diet, fish feed, formulation, growth

The study examined helminth parasites of cultured Clarias gariepinus and Tilapia zillii in Uyo, Akwa Ibom State. A total of 60 fish samples (30 each of C.gariepinus and T. zillii) were subjected to parasitological examinations. Results revealed a total of 47(78.33%) fishes infected with various species of parasites: Nematodes (Camallanus polypteri, Paracamallanus cyathopharynx, and Procamallanus laevionchus), Cestodes (Polyonchobothrium torulosus and P. clariae) and Trematodes (Dactylogyrus extensus and Glossiduim pedatum) in decreasing order of abundance. Out of the 60 fish samples examined, 47 were infected with 219 parasites: 142(64.84%) nematodes, 40(18.26%) cestodes and 37(16.89%) trematodes. A total of 159(72.60%) parasites were recovered from C. gariepinus out of which 103(64.78%) were nematodes, 19(18.45%) were cestodes and 37(35.92%) were trematodes. While 60(27.40%) parasites were recovered from T. zilli, of which 39(65.00%) were nematodes and 21(35.00%) cestodes. No trematode was observed in the tilapia. The overall prevalence of parasitic infection was 78.33%. The results of chi square analysis showed that females of both species had significantly higher (P<0.05) prevalence of infection 27(84.4%) than males 20(71.4%). Also, C. gariepinus had higher infection rate of 25(83.33%) when compared to 22(73.33%) recorded in T. zillii. Key words: fish parasites, aquaculture, prevalence, C. gariepinus, T. zillii

The postembryonic development of the gill parasite, Lamproglena clariae, infecting the sharp tooth catfish, Clarias gariepinus was established from egg culture and artificial infection of fish under laboratory conditions. Like most fish parasitic copepods, L. clariae has a direct life cycle utilizing only a single fish host species. Adult post metamorphosis females produce two egg strings. The mean number of eggs in each egg string was 52. Three naupliar and first copepodid stages were obtained in culture while two copepodid stages, cyclopoid and adult specimens were obtained after artificial infection of catfish in aquaria. First stage nauplii were globular in shape and densely filled with yolk. Nauplii lacked a perforation for the mouth and masticatory parts of the appendages, all of which indicate that they do not feed. Body architecture of the first copepodid stage of L. clariae is similar to that of all other copepods in the number and kind of somites: a cephalothorax with five appendages, three thoracic somites, one abdominal somite and furca rami. This seems to be a conserved morphology among the copepods. The three naupliar and three copepodid stages are described and compared to related copepods.

Inadequate seed production has historically been a factor limiting the commercial culture of Clarias gariepinus. The need to determine the environmental requirements of larvae was identified, in order to facilitate their successful mass rearing in hatcheries. The effects of key environmental factors on the growth, survival and aspects of the behaviour of C. gariepinus larvae and juveniles were investigated under controlled conditions. A strong emphasis was placed on the interpretation of the observed responses in terms of the natural history of the animal. Larvae were obtained by artificially inducing and spawning feral adult broodfish. Larval growth rates were highest in the temperature range 26-33ºC, with a peak at 30ºC. Survival of larvae was high between 22 and 33ºC. The final temperature preferendum of juveniles, determined in a thermal gradient was 30ºC, and it was concluded that this temperature is probably optimal for most of the physiological processes of the animal. Larvae and juveniles displayed strong negative phototaxis. When reared under different photoperiod regimes, larval growth increased with longer dark periods, however a similar rate of mortality was recorded in all photoperiod treatments. The provision of cover was found to enhance larval growth under conditions of continual light (24L/OD), however under conditions of continual darkness (OL/24D) similar growth rates were recorded regardless of the presence or absence of cover. All growth rates in continual darkness (OL/24D) were higher than those in continual light (24L/OD), regardless of whether cover was provided or not. It was concluded that a OL/24D photoperiod is optimal for larval rearing. At salinities between 0 and 5% similar growth and mortality rates of larvae were recorded. At 7.5 % larval growth and survival rates were lower, and at 10 % all larvae died within 48 hours. The 96h-LCSO for unionised ammonia was found to be 2.3 mg/l. The cytological effects of unionised ammonia were evident as degenerative changes in the gill and liver tissues. In an investigation of tank hygiene, it was found that larval growth and survival rates were highest in tanks not cleaned at all. As the frequency of tank cleaning increased, the growth and survival rates of larvae decreased. When reared at densities ranging from 45-450/1, larval growth was found to be density dependent. A model of hatchery productivity (number larvae of standard size produced/time/vol.) was developed based on the density dependent nature of larval growth. The model predicts that maximum productivity, will be achieved at a rearing density of 1400/1. The high growth and survival rates obtained over a broad range of each environmental parameter investigated serve to explain how larvae survive and grow in their unstable floodplain habitat in nature. The broad environmental tolerances of C. gariepinus are of benefit with respect to the culture of larvae, as successful larval rearing is possible over a fairly wide range of environmental conditions.

A rationale is presented for a primary nursing strategy and an on-growing strategy for Clarias gariepinus (Burchell) culture in Africa, thus providing a potential model for the development of culture technology for the species. Existing information pertaining to the production strategies identified is reviewed, highlighting the attributes of African catfish for aquaculture. Some of the current deficiencies and inconsistencies in available information pertaining to controlled hatchery production are addressed. The early developmental stages of Clarias gariepinus are defined, in order to promote consistent use of terminology and help farmers better address the changing needs of their developing stock. The pattern of growth and survival of larvae and fry is investigated at higher stocking densities than those used experimentally to provide a database for planning full-scale commercial operations. Tank design and water flow rates appropriate for Clarias gariepinus in hatcheries are investigated and recommendations made. Finally, in order to promote maximal growth rates of hatchery stocks the maximum daily feed intake of larvae in relation to different feeding regimes is estimated based on rates of gastric evacuation and return of appetite. An overview of the controlled hatchery production of Clarias gariepinus is presented.

Thesis (MPhil (Animal Sciences. Aquaculture))--University of Stellenbosch, 2005.
In recent years there has been a renewed interest in the commercial culture of African Sharptooth Catfish. Its robust characteristics and its air breathing capabilities makes the African catfish a good candidate for culture in intensive recirculating systems. In light of the size variation in offspring spawned from undomesticated fish, that may eventually increase cannibalism, suitable methods for the quantification of some production performance parameters such as growth and health measurements need to be established for application in intensive catfish culture. In fish the condition factor (CF) reflects information on the physiological state of the fish in relation to its welfare. This factor is expressed as Fulton’s condition index, or the K-factor. African Sharptooth Catfish fry with average weight of 1.9g ± 0.7867 and average length of 59.375mm ±8.812 were equally allocated into ten 1000L-recirculating tanks. The fish were fed a commercial feed to apparent saturation at a frequency of 5 times per day. Sixteen fish were sampled out of each treatment. Weight (g) and length (mm) of each fish were recorded every seven days over a trial period of 175 days from which Fulton’s condition index K was calculated. Results were analysed for significant differences using one-way ANOVA and Tukey’s pair wise comparison test for the various parameters. Growth parameters (a = -5.083, b = 3.004, R2 = 99.4%) derived from the logarithmic relationship between body weight (W) and standard length (L) indicated an isometric growth through the duration of the trail. No significant differences (P>0.05) in condition factors between treatments were found at the beginning of the trail. Significant differences (P<0.05) were found at the end of the trail for weight between ponds and condition factor between treatments. No significant difference (P> 0.05) between length and treatments were found at the end of the trial. Mean condition factor was 0.856 ± 0.187. By using this information on condition factor for African catfish a K-factor calculation chart for African catfish could be calculated, to be used as a practical measurement tool to measure performance goals on catfish farms.

Thesis (Ph.D. (Agriculture)) --University of Limpopo, 2015
The ability to utilise dietary components differs between fish species. Digestive enzymes may be used to determine the efficiency of the digestive process. In this study, the activities of the digestive enzymes in Tilapia rendalli, Oreochromis mossambicus and Clarias gariepinus were explored. Protease, amylase, lipase and cellulase activities were measured in different parts of the digestive tract of the three fish species. The pH dynamics along the digestive tract were monitored. In all fish species, the presence of food led to a reduction in stomach pH. pH values of 1.54, 1.58 and 2.01 were recorded 12 hours after feeding in Oreochromis mossambicus, Tilapia rendalli and Clarias gariepinus respectively. Protease and amylase activities were significantly higher (P<0.05, ANOVA) in the tilapias than in Clarias gariepinus. The tilapias may be pre-adapted to produce more protease and amylase to digest plant material which is more difficult to digest compared to animal matter. In all species amylase activity was significantly higher in the proximal intestine than in the other parts of the digestive tract (P<0.05, ANOVA). The highest proteolytic activity was recorded in the distal intestines. This is because of the alkaline pH recorded in the proximal and distal intestines which favours for amylase and protease activity respectively. Lipase activities were not significantly different (P>0.05) in all species. Marginal cellulase activities were recorded in all species. It is inferred here that phylogeny and not diet may be the main factor influencing enzyme activities as all fish were fed a similar diet. Two locally available plant diets, kikuyu grass and moringa leaves, were tested as protein sources in the diet of a macrophagous fish, Tilapia rendalli (11.5±1 g). Nine diets (30% CP: 20 MJ/kg) were formulated by substituting fishmeal for kikuyu leaf meal (KLM) and moringa leaf meal (MLM). A control diet contained 10% fishmeal and no leaf meal. Fishmeal was replaced at 25, 50, 75 and 100% by KLM in diets: KLM 25, KLM 50, KLM 75 and KLM 100; then by MLM in diets MLM 25, MLM 50, MLM 75 and MLM 100. Each diet was fed to triplicate groups of fish for 60 days. The best growth (SGR, TGC) was in the control group. There was no significant (P>0.05) decrease in SGR and TGC when KLM replaced up to 50% fishmeal. There was a significant (P<0.05) decrease when MLM replaced >25% fishmeal. Kikuyu diets had no effect on villi height. A trend towards shorter villi was evident with increasing MLM. Digestive enzyme activities also decreased with increasing KLM and MLM vii levels in the diet. Hepatocyte degradation was higher in fish fed moringa-based diets. Anti-nutrients (polyphenols, tannins, saponins and phytate) in moringa may have contributed to the poor growth, irritation of the enterocytes and hepatotoxic effects. These results show that replacing up to 25% fishmeal with KLM is effective in reducing the costs without negatively affecting the growth performance or health of Tilapia rendalli. Adding MLM, even at the lowest level (25%) was expensive and resulted in compromised growth and health. The efficacy of KLM and MLM was also tested as alternative protein sources for Oreochromis mossambicus (12.5±1 g) a microphagous herbivore. The same diets used for Tilapia rendalli were fed to triplicate groups of twenty fish for 60 days. Linear regressions of feed intake, SGR, PER and protein ADC with increasing levels of leaf meal were significant (P<0.05). Superior growth performance, protein ADC and feed utilisation were also recorded in fish fed KLM-based diets than those fed MLM diets. When compared to Tilapia rendalli, Oreochromis mossambicus had superior growth performance and feed utilisation when fed the control diets and the lowest level of KLM. This was attributed to phylogeny. Protease, amylase and lipase decreased with increasing leaf meal levels and were higher in the intestine of fish fed KLMbased diets than those fed MLM-based diets. Fish fed MLM-based diets had higher number of goblet cells in the enterocytes, higher hepatocyte degradation and poor haematological parameters than those fed KLM diets. These adverse alterations were more pronounced in Oreochromis mossambicus compared to those observed in Tilapia rendalli feeding of the same diets. Cost benefit analysis also indicated that substitution fishmeal with KLM is a cheaper protein source in Oreochromis mossambicus diets. Kikuyu leaf meal may be used to replace up to 25% fishmeal without compromising the growth performance and health of Oreochromis mossambicus. Reduced growth and poor health was evident even at the lowest inclusion level of MLM. The effects of replacing fishmeal with KLM and MLM in the diets of a predatory omnivore, Clarias gariepinus were also investigated. The same KLM and MLMbased diets used in the previous experiments were used. Each diet was randomly assigned to triplicate groups of Clarias gariepinus (30.5±2 g) and fed to apparent satiation for 60 days. Significantly higher (P<0.05) growth performance, feed and viii protein utilisation was observed in Clarias gariepinus fed KLM diets compared to those fed MLM. Protein digestibility was higher in Clarias gariepinus fed the control diet than in both tilapias. However, in the treatment diets protein ADC was lower in Clarias gariepinus than in the tilapias. A decrease in the activity of digestive enzymes was also observed with increasing leaf meal level in the diet. This was attributed to the natural feeding habits and digestive adaptations of the different fish species. No histological alterations were found in liver of fish fed the control diet. Increased hepatocyte degradation was seen in fish fed higher levels of KLM and MLM in the diet. The enterocytes showed a significant increase in the number of goblet cells with increasing levels of MLM. Villi height decreased significantly (P<0.05) when MLM replaced >75 fishmeal. The damage to the hepatocytes and enterocytes as well as the poor health condition shown by haematological parameters was more pronounced in Clarias gariepinus than in the tilapias. This suggests that the predatory fish is not equipped to utilise high levels of leaf meals in its diet. The results of this study indicate that KLM can replace up to 25% fishmeal and that adding MLM resulted in reduced performance. Higher profit index and lower incidence cost was observed KLM diets than in MLM diets. Anti-nutrients in the leaf meals were the main factors leading to reduced feed intake and poor growth in fish fed the plant-based diet. Therefore, a subsequent study was undertaken to determine the efficacy of exogenous enzyme supplementation to reduce the negative effects of anti-nutrients and improve fish growth. A commercial multi-enzyme Natuzyme50® was supplemented at a rate of 0 (control), 0.25, 0.5, 0.75 and 1.00 g/kg DM feed in the best performing diet (KLM 25). These diets were tested in Oreochromis mossambicus. Natuzyme50® supplementation led to improved growth performance. Fish fed the diet containing 0.50 g/kg had the best growth performance and protein ADC and highest levels of digestive enzyme activities. At higher (>0.50 g/kg) enzyme supplementation levels, growth performance decreased. The improved growth performance with enzyme supplementation was attributed to the presence of enzymes such as cellulase and xylanase in the cocktail that are not naturally produced by fish. In addition, the activities of endogenous enzymes were enhanced. The optimal Natuzyme50® dietary level for optimal growth performance in Oreochromis mossambicus was 0.62 g/kg DM feed.

The role of the lipid-soluble antioxidant α-tocopherol (vitamin E) in the nutrition of African catfish (Clarias gariepinus Burchell) has been investigated with respect to effects on growth, certain indices of health and prevention of tissue lipid peroxidation. Although juvenile C. gariepinus were not found to show an immediate dependency on vitamin E for growth, even during rapid growth stages, a minimum requirement of α-tocopherol based on the prevention of hepatic lipid peroxidation was established at 30-40 mg α-tocopherol per kg dry diet. This is in line with published values for numerous cultured fish species. Tissue α-tocopherol accretion was found to be dependent on dietary dose of the vitamin (supplied as all-rac-α-tocopheryl acetate) and, with the exception of blood-plasma, increased tissue tocopherol status resulted in increased stability against lipid peroxidation. Assessment of iron-ascorbate induced peroxidation (as TBARS) revealed that feeding catfish with diets containing a-tocopherol at several times the currently supplemented level, improved the stability of catfish muscle and this has fillet quality implications. Similarly, heightened fillet vitamin E content resulted in lower moisture exudation from previously frozen fillets, thus demonstrating the role of a-tocopherol in the maintenance of membrane integrity. Oxidation of dietary oils and elevated ingestion of iron were found to be antagonistic of tissue vitamin E concentration. Consumption of feed containing rancid oil had marked effects on tissue fatty acid composition and these effects were modulated by increased intake of α-tocopheryl acetate. In catfish fed diets containing similar amounts of ascorbate, a higher α-tocopherol supplement marginally improved ascorbate retention indicating a possible sparing of vitamin C by vitamin E. The present work will contribute significantly to the understanding of antioxidant nutrition in this poorly researched cultured species. Furthermore, these investigations have improved and strengthened the database of knowledge accumulated within the field of nutrition of finfish.

Invasive species are of particular concern as they have the potential to alter community structure and food web relationships within their invaded habitats. African sharptooth catfish Clarias gariepinus, a generalist predator, was introduced through an inter-basin water transfer scheme into the Great Fish and Sundays Rivers, Eastern Cape, South Africa, where it threatens the native riverine biota. This thesis assessed its impact from a trophic perspective. Patterns in catfish distribution and abundance revealed an upstream to downstream gradient that was associated with spatial distribution of most species within the mainstream, and a mainstream to tributary gradient that was associated with the spatial distribution of native minnows. The catfish was predicted to occur widely within the mainstem habitats and to decrease progressively along the mainstrem to tributary gradient with the physico-chemical environment being a good proxy for predicting both its occurrence and abundance. The results suggest the catfish proliferated within mainstem habitats where invasion resistance was possibly reduced due to alteration of flow. Population dynamics and size structuring of two native cyprinid minnows Pseudobarbus afer and Barbus anoplus, threatened by catfish, were examined within uninvaded headwater streams in relation to their proximate physical habitats. Their habitats were characterised by seasonal variation in physico-chemical conditions and a spatial variation in substrata compositions. No evidence of differences was found between seasons for density and capture probability for either species. The population size and density for P. afer was found to increase with increasing proportion of boulders. In comparison, B. anoplus population size and probability of capture increased with increasing proportion of bedrock and bank vegetation, respectively. Size structuring was explained predominantly by seasonality and habitat variables for P. afer and B. anoplus, respectively. Stable isotope ratios of carbon and nitrogen were used to compare the spatial variation in both the community-wide and catfish-specific niches and to estimate catfish prey sources from different habitats within the invaded systems. Aquatic community and catfish niches were statistically different among localities, suggesting that each locality had a distinct community-wide trophic structure. Dispersion metrics indicated no evidence of differences in the clustering among individuals, but provided evidence of differences in path trajectories for the comparisons of catfish populations that suggested dietary plasticity within different localities. Dietary studies revealed both ontogenetic shift and omnivory that suggested that catfish may exhibit less pronounced top-down effects within its invaded habitats. Manipulative experiments were used to test the response of benthic macroinvertebrates within two rivers that were differentially impacted by catfish as a presstype disturbance. Macroinvertebrates were non-responsive to catfish presence within a system where catfish had previously been established. In contrast, excluding catfish in this system indicated a response that suggested the importance of refuge within invaded habitats and the possible recovery pattern of certain macroinvertebrate taxa. By comparison, introduction of catfish within previously uninvaded localities provided evidence of direct catfish impact through elimination of conspicuous taxa. Acoustic telemetry was used to investigate catfish movement patterns within an invaded lentic habitat and provided evidence that habitat utilisation was non-random. The shallow and structured river mouth habitat, which was most utilised, was probably the most ideal for its breeding and feeding. This inferred potential overlap with native species and suggested the risk of predation and competitive interference. Catfish also exhibited both nocturnal and diurnal activity patterns that were probably related to feeding.

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Financiadora de Estudos e Projetos
Air-breathing fish are classified as obligatory (when breathing obligatory atmospheric air independently of the water O2 tension) or facultative air-breather (using an air breathing organ ABO -, when theirs gills are not able to extract all O2 necessary to maintain the aerobic mechanisms under hypoxic conditions). The catfish, Clarias gariepinus, is airbreathing fish that shows modifications on the gill lamella, forming a ventilatory fan, and on the 2o e 4o gill arches, forming an arborescent organ. These structures form the ABO of this specie.The objectives of the present study were: 1. To determine if C. gariepinus is an obligatory or a facultative air breather. 2. To analyze the cardio-respiratory responses ( VO2 - metabolic rate; VG - gill ventilation; VT ventilatory volume; fR respiratory frequency; EO2 O2 extraction from the ventilatory current; fH- heart frequency) in response to progressive hypoxia. 3. To verify if the critical O2 tension (PcO2) of this specie is correlated with the O2 uptake from the atmospheric air.To classify the air-breathing mode of C. Gariepinus, the fish (Wt ~ 350 g; n = 7) were maintained in normoxia during 24 hours without access to air. The fR maintained constant during all the experiment and there was no mortality, indicating that C. gariepinus is a facultative air-breather. To analyze the cardio-respiratory responses to progressive hypoxia, VO2 , EO2, fR, VT, VG , EO2 and fH were recorded under the following water O2 tensions(PwO2): 100, 70, 50 e 30 mmHg. Fish maintained a constant VO2 until the PcO2 (~ 55 mmHg), below which VO2 decreased significantly. This decreasing was followed with the significant reduction of EO2 in PinspO2 of 62,7 ± 1,30 mmHg reaching values of 19,6 ± 1,9 % in severe hypoxia. The VG and the VT increased progressively until PinspO2 of 28,0 ± 0,5 mmHg, reaching highest values of, respectively, 1545,7 ± 63,5 mLH2O.kg-1.min-1, 33,9 ± 0,8 mLH2O.Kg-1.resp-1 e 57,2 ± 1,4 resp.min-1. The fH reduced progressively from 43,4 ± 0,4 bpm, in normóxia, arriving significant values just above the PcO2 and reaching minimum values (19,2 ± 3,0 bpm) in severe hypoxia. Under progressive hypoxia (100, 70, 50, 30 e 20 mmHg) and with the access to the atmospheric air, C. gariepinus (Wt ~ 610 g; n = 9) presented a 5-fold increase in the air-breathing frequency (fRA). A bradycardia was observed just before the air breath and a tachycardia just after.Concluding, C. gariepinus is a continuous facultative air-breathing fish that regulate the 2 O V until the PcO2 of ~54 mmHg. Below this tension fish increase the VG mainly due to a larger increase of VT (lower metabolic cost of VG ). The hypoxic pre-air breath bradycardia is characteristic of aquatic breathers while the post-air breath tachycardia is typical of air respirators. The fRA increased proportionally with the progressive hypoxia, mainly just above the PcO2. These results show that C. gariepinus is adapted to survive at hypoxic habitats and that this species show a higher dependence of the atmospheric air than the others facultative air-breathing fishes.
Peixes de respiração aérea são classificados como respiradores aéreos obrigatórios (aqueles que respiram ar atmosférico independente das tensões de O2 da água) ou facultativos (aqueles que usam o órgão de respiração aérea ABO quando as brânquias não conseguem extrair a quantidade de O2 necessário para manter o metabolismo aeróbico em condições hipóxicas). O bagre-africano, Clarias gariepinus, é um peixe de respiração aérea que apresenta modificações na lamela branquial, formando um leque ventilatório, e, nos 2os e 4os arcos branquiais, os órgãos arborescentes. Estas últimas estruturas formam o ABO desta espécie.Os objetivos do presente estudo foram: 1. Determinar se C. gariepinus é um respirador aéreo facultativo ou obrigatório. 2. Analisar as respostas cardiorrespiratórias ( VO2 - taxa metabólica; EO2 - extração de O2 da corrente ventilatória; VG - ventilação branquial; VT - volume ventilatório; fR - frequência respiratória; fH- frequência cardíaca) em resposta a hipóxia gradual. 3. Verificar se a tensão crítica de O2 (PcO2) desta espécie está relacionada com a tomada de O2 do ar atmosférico.Para classificar a modalidade da respiração aérea de C. gariepinus, os peixes (Wt ~ 350 g; n = 7) foram mantidos em normóxia durante 24 h sem acesso ao ar atmosférico. A fR manteve-se constante durante todo o experimento e não houve mortalidade, indicando que C. gariepinus é um respirador aéreo facultativo. Para analisar as respostas cardiorrespiratórias em normóxia (controle) e hipóxia gradual, a VO2 , EO2, fR, VT, V G e fH foram registradas durante as seguintes tensões de O2 (PwO2): 100, 70, 50 e 30 mmHg. Os peixes mantiveram VO2 constante até a PcO2 (~ 55 mmHg), abaixo da qual a VO2 decresceu significativamente. Esta diminuição da VO2 foi acompanhada da diminuição significativa da EO2 em PinspO2 de 62,7 ± 1,30 mmHg atingindo valores de 19,6 ± 1,9 %, em hipóxia severa. A VG , VT e fR aumentaram progressivamente até a PinspO2 de 28,0 ± 0,5 mmHg, chegando a valores máximos de, respectivamente, 1545,7 ± 63,5 mLH2O.kg-1.min-1, 33,9 ± 0,8 mLH2O.Kg-1.resp-1 e 57,2 ± 1,4 resp.min-1. A fH diminui progressivamente de 43,4 ± 0,4 bpm, em normóxia, até alcançar valores significativos próximos a PcO2 e valores mínimos em hipóxia severa (19,2 ± 3,0 bpm). Em experimentos de hipóxia gradual (100, 70, 50, 30, 20 e 10 mmHg) com acesso ao ar atmosférico, C. gariepinus aumentou aproximadamente 5x a frequência de respiração aérea (fRA). Em cada tensão hipóxica ocorreu uma bradicardia pré-RA seguido de taquicardia significativa pós-RA (típico de respiração aérea); a fR manteve-se praticamente constante (~ 32 resp.min-1) até as duas últimas PwO2 (20 e 10 mmHg), nas quais a fR diminuiu para 23,0 ± 1,18 resp.min-1.Finalmente, C. gariepinus é um peixe de respiração aérea facultativa contínua que regula a VO2 até a PcO2 de ~ 55 mmHg. Abaixo desta tensão o animal aumenta a VG devido principalmente a um pronunciado aumento na VT (diminuição do custo metabólico da VG ). A bradicardia hipóxica pré-RA é uma característica de respiradores aquáticos, enquanto a taquicardia hipóxica pós-RA é típica de respiradores aéreos. A fRA aumentou proporcionalmente com a hipóxia gradual, principalmente próximo a PcO2. Tais resultados demonstram que C. gariepinus está adaptado a sobreviver em habitats hipóxicos e demonstra uma maior dependência do ar atmosférico do que outros respiradores bimodais facultativos.

Thesis (M. Sc. (Agriculture)) -- University of Limpopo, 2016
Fish assemblages in relation to environmental variables within the Broederstroom and Debengeni Rivers were investigated. Both rivers were characterized by coarse substrates (pebble and gravel), temperatures below 20°C and moderate depth. Trout dominated fish assemblages in terms of numbers caught and was only distributed at higher altitude sites >1400 m (a.s.l). Coarse substrates, temperatures below 15°C, flow rate, depth and riparian cover were the variables shown important for the distribution of trout by multivariate analysis. The confinement of the trout to higher altitude and lack of optimal habitat variables at lower altitude sites contributed to the assertion that the area is marginal for trout distribution. It was therefore inferred that the marginality of the area is the possible explanation for trout failure to self-sustain its population, therefore dependent on the continuous restocks by the local hatchery. The continuous restocks of small size trout in the Broederstroom River prompted a subsequent study where trout’s impact on macroinvertebrate communities was evaluated through surveys and field experiments. The ability of small trout to utilize macroinvertebrates made them suitable candidates to evaluating their impact in the area. Aquatic invertebrates were found to be the main food source for the trout in the area. Taxa such as Gomphidae and Potamonautidae were the most frequent food items from the analyzed stomachs of trout. However, observations from both field surveys and experiments showed that trout is a weak regulator of macroinvertebrate diversity in the area, since there were no significant differences (ANOVA, P<0.05) in the diversity of invertebrates from trout invaded and uninvaded sites. Trout being a weak regulator of macroinvertebrate diversity in the area, it prompted surveys to the Ebenezer Dam to determine its competitive interactions with native predatory species. If the introduced species is a more efficient predator than the native predator species, it may affect changes in the structure of the habitat and food resource. Trout in the Ebenezer Dam was found to be selective to habitat variables whilst C. gariepinus was cosmopolitan to all habitat categories. The catfish also had a broader food preference than trout and the diversity of the food items was significantly different (ANOVA, P<0.05) between the two species. Unfortunately, the interspecific food overlap between trout and the catfish could not be determined in Ebenezer Dam, because of the small sample size of trout but food selection between vii them was evident. It was then concluded that the native catfish has a wider niche and it is a more efficient predator than the introduced trout. This observation contributed further to the assertion that the area is marginal for trout to thrive. Due to trout selection of habitat variables, it became prudent to carry out another study where the past climate and land use changes were analyzed to determine their effect on the habitat that could have affected the distribution of trout in the area. Future projections were also made to determine possible future impacts of climate change on the distribution of trout in the area. The effects of climate and land use change resulted in warmer water temperature, altered riparian cover and altered stream flow patterns. The changes could have influenced the confinement of trout to higher altitude catchments. The projected maximum temperatures by 2050 shows an increase from 2014 with a decline in precipitation. If these projections are to be the same for water temperature and flow regimes, coupled with current land uses in the area, they will continue to affect the distribution of trout negatively.