Artificial Spawning of African Catfish,Clarias gariepinus

Abstract

The effects of controlled reproduction of African catfish, Clarias gariepinuswere investigated in an experiment with carp pituitary (at the dose 4 mg/kg body weight) or Ovopel (1 pellet/kg body weight) used as ovulation stimulators. The application of the synthetic stimulator led to the significantly (P≤0.01) greater weight of eggs (expressed in grams and as percentage of female body weight) and to the significantly (P≤0.05) higher quality of eggs after 24-hour incubation as compared with the hypophysation effects. Two categories of females were used in the experiment, i.e., light (mean body weight of 3.75 kg) and heavy (mean body weight of 8.86 kg) fish. The results show that a significantly (P≤0.01) greater weight of eggs (expressed in grams) was obtained from heavier females. The quality of eggs expressed as the percentage of live embryos after 12- and 24-hour incubation was significantly (P≤0.01 and P≤0.05, respectively) higher for lighter females. The higher weight of obtained eggs and their better quality after Ovopel stimulation compared to the weight and quality of eggs obtained after hypophysation allow for the recommendation of this ovulation stimulator for the fish species investigated.     

Stunning of farmed African catfish (Clarias gariepinus) using a captive needle pistol; assessment of welfare aspects

The objective of this study was to assess whether high‐pressure injection of air into the brain of African catfish (Clarias gariepinus) could render the animal unconscious and insensible immediately and permanently. In the study, 48 African catfish with a live weight of 900–1900 g were restrained and equipped with EEG and ECG electrodes and then stunned. The catfish were stunned mechanically using a captive needle pistol. The pressure to shoot the needle was 8 bar and that to inject the air was 3 bar for 1.5 s. The catfish behaviour was observed during and after stunning. τ and δ waves and spikes, which precede a stoppage in brain activity as measured on the EEG, were used as indices for the measurement of immediate induction of unconsciousness and insensibility In 23 of 42 fish, an iso‐electric line was observed after an average of 13.4 s, while in the remaining fish the τ and δ waves and spikes remained on the EEG during the recording period. In all cases, the ECG showed an irregular heart rate with fibrillation and extra systolae. Moreover, the configuration showed ischaemia. Before the captive needle stunning, free‐swimming fish (n=7) explored the tank for an average of 21±12 s before lying down at the bottom. After stunning, they showed clonic uncoordinated swimming movements. The movements stopped after an average of 38±50 s. In another group (n=7) that was stunned and subsequently placed in ice water, clonic cramps were observed in two out of seven animals. When taking into account the number of animals with a reliable EEG (n=42) and using 95% confidence intervals, it was concluded that at least 93% of the catfish were effectively stunned using a correctly positioned captive needle pistol. Furthermore, it is recommended to immobilize the stunned fish by chilling, as the post‐stun clonic cramps may hinder gutting and filleting.     

Characterization of the testicular semen of the African catfish, Clarias gariepinus (Burchell, 1822), and its short-term storage

Semen of the African catfish, Clarias gariepinus (Burchell, 1822), was investigated with respect to its cellular composition, sperm cell density, maturation grade, motility and fertility. Storage conditions were tested, whereby sperm viability was assessed by measurement of the motility after activation and by fertility tests. Testicular semen differed in its composition, i.e. the sperm density and numbers of spermatids, according to the maturity grade of the testis. Two semen types could be distinguished: semen type I was characterized by high sperm densities and low numbers of spermatids and semen type II had lower sperm densities and higher numbers of spermatids. Two semen types did not differ in motility and fertility (when adjusted for differences in sperm density). During storage, the sperm viability was influenced by the sodium concentration of the storage medium, temperature, membrane stabilizers as bovine serum albumen (BSA) or hen egg yolk, antibiotics and oxygen. Semen viability was maintained best when it was diluted at a ratio of 1:5 in storage solution (150 mmol L^?1 NaCl, 2.5 mmol L^?1 KCl, 1 mmol L^?1 CaCl₂, 1 mmol L^?1 MgSO₄, 20 mmol L^?1 Tris (pH 8.5) and 0.5% BSA or 0.5% hen egg yolk) and stored at 4 °C. Oxygen gassing and addition of antibiotics (1 mg mL^?1 gentamycine sulphate) to the storage solution affected the two semen types in different ways. Antibiotics had no effect on type I semen, but had a positive effect on type II semen. Oxygen gassing had a positive effect on type I semen but a negative effect on type II semen.     

Modulation of tissue α-tocopherol in African catfish, Clarias gariepinus (Burchell), fed oxidized oils, and the compensatory effect of supplemental dietary vitamin E

Juvenile African catfish, Clarias gariepinus (Burchell), of mean initial weight 15 g, were fed practical diets containing fresh or rancid oil (1:1 cod liver:corn oil) supplemented with either 20 or 100 mg all-rac-α-tocopheryl acetate per kg dry diet, at 0.03 × body weight per day for 8 weeks. After this time, catfish had grown by at least four times in body weight. Significant ( P < 0.05) inter-treatment differences in final body weight were noted. Clarias fed low-tocopherol: oxidized-oil diets performed least well with regard to growth, though elevated dietary vitamin E partially abrogated this effect. Growth of fish fed fresh-oil diets did not benefit from increased dietary α-tocopherol content. Muscle, liver, plasma, heart and spleen all responded significantly ( P < 0.05) to dietary vitamin E dose. Inclusion of oxidized oil in catfish diets decreased tissue α-tocopherol concentration. Hepatic α-tocopherol concentration (μg α-tocopherol per g liver) was observed to be lowered by 90% by the rancid oil diets. When fish previously fed fresh-oil diets were switched to oxidized: low-tocopherol diets, hepatic α-tocopherol concentration was significantly ( P < 0.05) lowered within 2 weeks. The results highlight the importance of dietary oil quality in modulating tissue α-tocopherol concentrations in African catfish.     

Phosphorus utilization in juvenile Clarias gariepinus fed phytase-supplemented diets based on soya bean (oil-extracted) and full-fat (roasted): A comparison

The effect of microbial phytase on phosphorus utilization in juvenile Clarias gariepinus (initial fish body weight 11.55 ± 0.2 g) was tested on two different diets based on oil-extracted soya bean (Experiment 1) and roasted soya bean meal (Experiment 2) using a 5 × 5 experimental design for 84 days. The basal isonitrogenous and isocaloric diets for oil-extracted and roasted soya bean were formulated to replace fish meal at 25% (S1E), 50% (S2E), 75% (S3E), 100% (S4E); and 25% (S1), 50% (S2), 75% (S3), 100% (S4), respectively. Each treatment was replicated four times. Microbial phytase was supplemented in each replicate at 250 FTU/g (P1), 500 FTU/g (P2), 750 FTU/g (P3), and 1,000 FTU/g (P4). Basal controls, which included a fish meal-based diet (S0), were not supplemented with phytase (P0). The result in Experiment 1 showed that there was a significant increase in whole-body protein and reduction in fat with phytase compared to a diet without phytase (P < 0.05). Serum total protein declined significantly with phytase supplementation (P < 0.05). Serum phosphorus and glucose were higher with phytase supplementation compared to control (P < 0.05). Bone minerals declined significantly with increasing level of soya bean compared to fish meal diet (P < 0.05). In Experiment 2, serum phosphorus was improved with phytase compared to control with no phytase (P > 0.05). A significant reduction in whole-body protein and increase in fat was observed for fish fed phytase diets compared to diets with no phytase, regardless of soya bean level (P < 0.05); however, ash content was improved with phytase (250 FTU/g) compared to control (P < 0.05). Phytase supplementation improved bone phosphorus (250 FTU/g), calcium (250 FTU/g), magnesium (250–500 FTU/g), and zinc (250–1,000 FTU/g) compared to control (P < 0.05). In conclusion, the research has demonstrated that improved bone phosphorus (P) and growth could be achieved with the supplementation of dietary phytase.     

The growth and gonadal maturation of the African catfish, Clarias gariepinus (Burchell) broodstock fed differently heated soybean-based diets

An investigation was carried out to assess the growth and gonadal maturation of Clarias gariepinus (Burchell) fed differently heated soybean diets in concrete tanks. Four hundred and eighty male and female C. gariepinus (182 ± 10 g for females and 208 ± 5 g for males) were randomly distributed in groups into hapa nets. Iso‐nitrogenous (310 g kg^?1 crude protein) and iso‐caloric diets (355 Kcal kg^?1) prepared from raw soybean (D0) and soybean autoclaved for 5, 10, 15, 20, 25 and 30 min labelled D0, D5, D10, D15, D20, D25 and D30, were fed to the fish for 84 days. The fish meal based diet tagged DFM served as control. The male and female broodfish fed the fish‐meal‐based diet and diet D25 had significantly higher (P < 0.05) growth performance, gonad maturation, gonadosomatic index, relative fecundity and percentage egg fertilization and hatchability than the fish fed the other diets. The females had significantly higher (P < 0.05) weight increases and healthier condition over their male counterparts fed the same diets. This study showed that diet D25 was found to be the best substitute for fish meal that provided adequate nutrients required for the formation of genital products that produced strong offspring in C. gariepinus broodstock culture.     

The influence of food particle size on gastric emptying and growth rates of fingerling African catfish, Clarias gariepinus Burchell, 1822

This study investigates the effect of feed particle size on gastric evacuation and growth of fingerling African catfish, Clarias gariepinus . Fish (0.97 ± 0.07 g) held in 40-cm diameter tanks at a stocking density of 5 fish L^–1 (25 fish per tank) were presented with one of four sizes of food particles (1, 1.5, 2 and 3 mm diameter). Gastric evacuation rate could be described by an exponential function with small feed particles being evacuated more rapidly: values of 0.076, 0.054, 0.047 and 0.029 were observed for fish fed 1 mm, 1.5 mm, 2 mm and 3 mm food particles, respectively. Growth rates were highest for fish fed the 1.5 and 2 mm pellets. Based on these findings, recommendations are made on the optimum food particle size for C. gariepinus fingerlings.     

Evaluation of mixed feeding schedules with respect to compensatory growth and body composition in African catfish Clarias gariepinus

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate compensatory growth and body composition in African catfish Clarias gariepinus (13.05 ± 0.05 g). A fishmeal‐based diet containing 350 g kg^?1 protein and 17.5 kJ g^?1 gross energy was fed to triplicate groups of 20 fish (per 30‐L tank). Fish were fed the diet either to satiation or feed restricted in six feeding schedules as satiation 56 days; restricted 28 days + satiation 28 days; restricted 14 days + satiation 14 days; restricted 7 days +satiation 7 days; restricted 3 days + satiation 4 days; and restricted 2 days + satiation 2 days. The restricted regime was achieved by offering fish 1% (maintenance ration) of their body weight per day adjusted after fortnightly weighing. African catfish showed partial compensatory growth under alternating periods of feed restriction and satiation feeding with significantly different values (P < 0.05) from fish fed in satiation throughout. However, significantly indifferent (P > 0.05) values of feed, protein, lipid and energy utilization were found under alternating periods of feed restriction and satiation feeding. Significantly higher (P < 0.05) feed intake was observed in treatment with satiation throughout than those in other treatments. All the feeding schedules showed no significant differences (P > 0.05) on body composition, organ indices, eviscerated carcass composition, viscera lipid and liver lipid. These studies reveals that C. gariepinus showed partial compensatory growth responses at alternating periods of restricted and satiation feeding.     

Growth and health performance of African catfish Clarias gariepinus (Burchell 1822) juvenile fed with graded levels of biofloc meal

The objective of the study was to evaluate the utilization of biofloc meal as a feed ingredient in enhancing the growth and health status of African catfish (Clarias gariepinus) juvenile. The study consisted of two experiments, that is digestibility and growth experiments. The digestibility of two biofloc meals produced with two different carbon sources, that is tapioca and molasses, were assessed in the digestibility experiment. Whereas the effect of four dietary treatments with different levels of biofloc meal, that is 0%, 5%, 10% and 20%, on the fish growth performance, feed utilization, immuno‐haematological response, antioxidant status and robustness against environmental stress were evaluated in the growth experiment. The results showed that the digestibility of dry matter, protein, lipid and phosphorus of biofloc grown using molasses as the carbon source were remarkably higher than that grown using tapioca (p < 0.05). The inclusion of biofloc meal in the diets at 10% and 20% resulted in higher feed intake, fish growth and final biomass and protein efficiency ratio, and lower feed conversion ratio (p < 0.05). Furthermore, the red blood cells counts, phagocytic, lysozyme activities and antioxidative capacity were significantly enhanced in the fish provided with diet containing 20% biofloc meal (p < 0.05).The fish survival following salinity stress test was higher in the treatments with biofloc meal at 10% and 20% inclusion levels. In conclusion, dietary inclusion of biofloc meal could improve the growth performance and health status of African catfish juvenile and an inclusion level of 20% could be recommended.     

Effects of density,PVC‐tubes and feeding time on growth,stress and aggression in African catfish (Clarias gariepinus)

Successive exposure to aquaculture‐related stressors may compromise the allostatic capacity of African catfish and lead to allostatic overload and poor welfare. Therefore, we tested the effect of (i) feeding during the light or dark phase, (ii) density (51 fish per 140 L versus 51 fish per 43 L) and (iii) altered available resting space/shelter on stress handling were studied in African catfish (Clarias gariepinus). Available resting space/shelter was manipulated by providing PVC‐tubes in the tanks. Growth, baseline stress load (cortisol and osmolality), metabolism (glucose, lactate and non‐esterified fatty acids) and aggression (measured by skin scar incidence) were assessed. Upon completion of the experimental period, we determined the adaptive capacity of the fish by the response to air exposure. We show that night‐feeding enhances growth and lowers feed conversion ratio compared to day‐feeding. No effects of density were found for baseline stress hormones, basal metabolism or aggression. Low density seems to stimulate aggressive behaviour after air exposure. Unexpectedly, providing PVC‐tubes under high‐density conditions increased aggression, raised baseline cortisol levels and decreased basal metabolism as well as growth; also the endocrine response to air exposure was stronger. We argue that these effects relate to a reduction in available space, i.e. a further increase in density, or to an increased competition for shelter. Overall, our data suggest that night‐feeding optimizes growth and that care should be taken in using objects as shelter/enrichment for African catfish.     

Effect of Salinity on Embryonic Development,Hatchability, and Growth of African Catfish,Clarias gariepinus,Eggs and Larvae

Abstract

Effects of salinity on embryonic development and growth of African catfish, Clarias gariepinus, eggs and larvae were studied. Eggs were incubated at 27-29°C in 2,4,6,8, and 10 ppt sodium chloride. Rate of embryonic development was delayed in all salt solutions by 15, 15,28 and 30 minutes, in 2,4,6, and 8 ppt sodium chloride, respectively, when compared with the control group (0% salt); total mortality occurred at 12 hours after gastrula stage in the 10 ppt concentration. Percentage hatching was 45.1,47.7, 59.5,49.2, and 26.6% while percentage deformity was 10.4, 16.1, 52.0, 28.6, and 71.6% in 0, 2, 4, 6, 8, and 10 ppt salt treatments, respectively. There were significant differences (P <0.05) in the hatching percentage and in deformity percentage between 4, 6, and 8 ppt. Rate of yolk absorption was significantly faster in the control and 2 ppt salt treatments, but slower in 4, 6, and 8 ppt. Rate of increase in length was slower with increasing salinity. The optimum salinity for African catfish eggs and was between 0-2 ppt and acceptable up to 6 ppt. The results suggest that increasing salinity delayed hatching and development of African catfish eggs and larvae, respectively, as well as increased the deformity of the larvae.     

Effect of feeding time and frequency on the growth and feed utilization of African catfish Clarias gariepinus (Burchell 1822) fingerlings

The effects of feeding time and frequency on the growth, feed utilization and survival of Clarias gariepinus (Burchell 1822; family Clariidae) fingerlings were evaluated in a 25-day study. Groups of African catfish with an initial individual weight of 0.98 ± 0.02 g were offered feeds continuously for 24 h, or during the day or night at different time intervals, with varying meal size. The growth rate was significantly affected by meal times. Widely practised day time feeding with three equal size meals a day gave the lowest growth and highest food wastage. The growth rates of fish fed continuously or during night time following their feed demand were significantly higher with lowest food conversion ratios and food wastage.     

Amino acid profiles and amino acid utilization in larval African catfish (Clarias gariepinus): effects of ontogeny and temperature

The present study investigated the qualitative amino acid (AA) requirements of larval African catfish Clarias gariepinus. Yolk-sac larval AA profiles were measured at different temperatures and also in animals reared at 28 °C fed Artemia nauplii or an experimental dry diet. The AA profile of C. gariepinus larvae changed during ontogeny, especially before the start of exogenous feeding. The AA profiles of the food items (yolk, Artemia and the dry diet) differed considerably from that of the larvae. No selective absorption of yolk AA was detected. Higher temperatures led to increased absorption and depletion rates of AA, and also to a higher retention efficiency of yolk nutrients. However, changes in temperature did not induce preferential absorption or depletion of individual AA, and caused only small variations in the AA profile. Depletion rates of individual AAs varied, possibly due to differences between larval and yolk AA profiles, and also to changes in the larval AA profile during ontogeny. There was little regulation of catabolism of individual AA in yolk-sac and starved larvae, and no sparing of essential AA.     

Use of full-fat winged bean Psophocarpus tetragonolobus seed meal as a protein feedstuff in fish-meal free diets for African catfish Clarias gariepinus

Mature winged bean Psophocarpus tetragonolobus seeds were quick-cooked and the full-fat meal derived was used to completely replace menhaden fish meal as a dietary protein source for the African catfish Clarias gariepinus . Five dry practical diets (400 g crude protein kg⁻¹ and 17.5 kJ gross energy g⁻¹ dry diet) containing menhaden fish meal (diet 1) or winged bean meal with or without graded levels of supplemental L -methionine (diets 2, 3, 4 and 5; 0, 5, 10 and 15 g kg⁻¹, respectively) were fed to catfish fingerlings (5.8  +  1.2 g) for 70 days. Weight gain, growth rate, feed conversion and protein utilization by catfish fed a winged bean meal diet without L -methionine supplementation (diet 2) was inferior ( P  > 0.05) to that in catfish fed the other diets, where performance differed nonsignificantly. Carcass protein of catfish was lower ( P  < 0.05) while liver protein was higher ( P  < 0.05) in catfish fed the winged bean meal diet without methionine supplementation. Results suggest that winged bean meal cannot replace fish meal as a protein source in catfish diets except with a minimum supplementation with 5 g L -methionine kg⁻¹ diet.     

Approaches to optimizing dietary protein to energy ratio for African catfish Clarias gariepinus (Burchell, 1822)

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate protein to energy ratio (P/E ratio) in African catfish Clarias gariepinus (10.9 ± 0.04 g). Six fishmeal‐based diets of two protein levels (330 and 430 g kg^?1), each with three lipid levels (40, 80 and 120 g kg^?1) resulted in P/E ratios ranging from 15.5 to 21.3 mg protein kJ^?1 gross energy (GE) were fed to 20 fish (per 30‐L tank) in triplicate. Fish were fed 50 g kg^?1 of their body weight per day adjusted fortnightly. Significantly higher (P < 0.05) growth rates and feed conversion efficiency were evident in fish fed with higher protein diet. The highest growth rate was found by fish fed 430 g kg^?1 protein, 21.2 kJ^?1 GE with a P/E ratio of 20.5 mg protein kJ^?1 GE. Significantly indifferent (P > 0.05) values of protein utilization were found in‐between the both (higher and lower) protein diets. Higher lipid deposition (P < 0.05) in whole body and liver was observed with increasing dietary lipid level at each protein diet and as higher (P < 0.05) for the lower protein diets. Liver glycogen tended to decrease with increasing gross energy at each protein diet and higher protein diet showed comparatively lower values (P > 0.05). Digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying P/E diets found no significant differences in response to experimental diets. The study reveals that African catfish C. gariepinus performed best the diet containing 430 g kg^?1, 21.2 kJ g^?1 and 20.5 mg protein kJ g^?1 GE protein, gross energy and P/E ratio, respectively.     

Salinity influence on the early stages of the African catfish

Experiments were conducted to determine the effect of various incubation salinities on the hatching and survival of eggs and hatched fry respectively of the African catfish (Clarias gariepinus). The optimal salinity for the hatching of the eggs ranged from 0–5. Above 5, hatching was significantly low and no hatching occurred at 8 incubation salinity. Median lethal times (LT50) for fry hatched in 0, 2 and 4 incubation salinities, when abruptly transferred to 10 were 59, 49.5 and 50 h respectively. Similarly, LT50 for fry hatched in 0, 2 and 4 incubation salinities, and abruptly transferred to 12 salinity were 17, 22 and 12.50 h respectively. Increase in incubation salinity of the eggs did not seem to enhance the salinity tolerance of the hatched fry.The gradual (stepwise) increase in salinity of 1 per day of the catfish fry hatched in various incubation salinities (0, 1, 2, 3, 4, 5 and 6) had median lethal salinity values of 8, 8, 8, 10, 10, 11 and 11 respectively. © Rapid Science Ltd. 1998     

Swim-up fry production in the African Catfish Clarias gariepinus (Burchell) broodstocks fed with differently heated soybean-based diets

Four hundred and eighty matured yearlings of Clarias gariepinus (Burchell) (female=182±10 g; males=208±5 g) distributed into groups of 30 specimens (sex ratio 1:1) were fed differently heated soybean‐based diets. Seven approximately iso‐nitrogenous (31% crude protein) and iso‐caloric (13.97 kJ g^?1) diets were prepared from either raw soybean (SAMSOY 2, TGX 636–02D) or soybean seeds autoclaved for 5, 10, 15, 20, 25 and 30 min. The untreated and the variously heat‐treated soybean meals were mixed with other ingredients to prepare diets designated as DSoy0, DSoy5, DSoy10, DSoy15, and DSoy20, DSoy25 and DSoy30 according to the treatment time of the soybean portion of the diets, and were fed to the fish broodstocks for 84 days. The fishmeal‐based diet (DFM) served as the reference diet. The duration of heating soybean component of the experimental diet significantly (P<0.05) affected the growth performance and the number of eggs produced by the broodstocks, the percentage number of eggs fertilized and hatched as well as the survival of the progenies. The progenies of the brood fish fed diets DFM and DSoy25 with a yolk sac size of 2.78±0.6 and 2.42±0.5 mm, respectively, had significantly (P<0.05) larger yolk sacs, which were also absorbed at a significantly faster rate of 0.61±0.02 and 0.51±0.03 mm day^?1, respectively, than progenies of broodstocks fed other experimental diets. Swim‐up fry survival rates were also better in hatchlings from broodstocks fed DFM (89.5%), DSoy25 (83.8%) and Dsoy 20 (80.5%) diets than progenies from other experimental diets. This study showed that soybean meal portion processed at 116°C and 1.2 kg cm^?2 pressure for 25 min in the diet, which ensures normal reproductive function and production of healthy progenies in C. gariepinus, could serve as a substitute for fishmeal in the broodstock diets.     

Effects of red clover extract on growth performance and body composition of African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis>

ABSTRACT:   The present study was conducted to investigate the effects of the red clover extract on growth, body composition and survival of African catfish Clarias gariepinus . Three concentrations (25, 50 and 75 mg/kg) of red clover at dietary were used for 120 days. The final weights of red clover-treated groups were significantly different from each other and the control group. The best growth was observed in the group receiving the 75 mg/red clover kg diet. Fish fed with all levels of red clover had higher weight gains than the control. The highest values of the specific growth rate and the food conversion rate were 1.14 ± 0.01 and 2.26 ± 0.04, respectively, for the 75 mg/red clover kg diet group. During the red clover administration period, the survival ranged from 97.78% for the 50 p.p.m. group to 95.56% for the 25 and 75 p.p.m. groups. Protein contents of the dosage groups were significantly different from control ( P  < 0.05). The highest value of protein content (19.97%) was observed for the 75 mg/ red clover kg diet. Lipid and ash contents were significantly affected by the red clover levels in the diets. The highest lipid contents were in the 75 mg/red clover kg diet (4.67%), and the highest ash content was 1.39% for the 25 mg/red clover kg diet.     

Digesta viscosity, nutrient digestibility and organ weights in African catfish (Clarias gariepinus) fed diets supplemented with different levels of a soluble non-starch polysaccharide

The objective of the present study was to investigate if dietary soluble non‐starch polysaccharides (NSP) increase digesta viscosity, reduce nutrient digestibility and increase organ weights in African catfish. The fish (mean weight 80 g) were fed diets supplemented with the soluble NSP guar gum at three levels, 0 g kg^?1 (GG0), 40 g kg^?1 (GG4) and 80 g kg^?1 (GG8). Guar gum inclusion significantly increased digesta viscosity in the proximal (GG0: 1.7 centipoise or cP; GG4: 84.9 cP; GG8: 98.3 cP) and distal (GG0: 1.9 cP; GG4: 109.8 cP; GG8: 66.4 cP) intestine. Apparent digestibility coefficients (ADC) were significantly lower for the GG8 diet than the GG0 diet (dry matter: 52% versus 69%; protein: 77% versus 90%; ash: 41% versus 54%; energy: 60% versus 77%). The ADC of dry matter and energy were significantly lower for the GG4 diet than the GG0 diet. The relative growth rate of metabolic weight (14.5–15.4 g kg^?0.8 day^?1) and feed conversion ratio (0.8) did not differ between diets. Fish fed the GG8 diet had a significantly higher somatic stomach index than GG0 fish (0.71% versus 0.65% body weight). The intestinal somatic index tended to increase with increasing guar gum supplementation (GG0: 1.08%; GG4: 1.23%; GG8: 1.59%). In conclusion, high digesta viscosities in the guar gum fed fish may explain the observed reduced nutrient digestibilities and increases in digestive organ weights.     

An evaluation of radiography in studies of gastric evacuation in African catfish fingerlings

Groups of 3–4 g African catfish (Clarias gariepinus Burchell, 1822; Family: Clariidae) were offered feeds of two types in three combinations: feed with a radio-opaque marker (Ballotini, 0.16–0.25 mm), feed without marker and a 50:50 mixture of marked and unmarked feeds. Stomach contents were estimated by X-radiography and gastrectomy just after meal termination and at different time intervals (4, 8, 12, 16, 20, 24, 32, 40 and 48 h). There were no significant differences among treatment groups confirming that there was no effect of the marker on feed preference and evacuation rate. Estimations of gastric evacuation rate calculated from gastrectomy and by X-ray sampling were not significantly different. Therefore, gastric evacuation rate of African catfish can be accurately estimated by feeding marked feed and then using X-radiography to monitor feed passage through the gut. © Rapid Science Ltd. 1998