Use of soybean flour (dehulled, solvent-extracted soybean) as a fish meal substitute in practical diets for African catfish, Clarias gariepinus (Burchell 1822): growth, feed utilization and digestibility

Growth and digestibility trials were conducted using African catfish, Clarias gariepinus (Burchell 1822): (1) to obtain apparent digestibility coefficient (ADC) values for capelin fish meal, soybean flour and corn meal; (2) to formulate diets based on ADC values of the protein feedstuffs; and (3) to evaluate the effects of replacing 25%, 50% and 75% of fish meal in control diets with soybean flour on growth, feed utilization efficiency and carcass composition. Supplemental methionine was added to the diet formulation in which soybean flour replaced 75% of the diet. Diets were formulated (400 g digestible protein kg⁻¹ and 15 kJ digestible energy g⁻¹ dry diet) and fed to catfish fingerlings (13.1 ± 0.5 g) to apparent satiation twice daily for 70 days. The protein and energy digestibilities of fish meal and soybean flour were high (>90% and >80%, respectively; P < 0.05). At 75% fish meal replacement with soybean flour (without methionine supplementation), growth and feed utilization efficiency indicators were depressed compared with other diet treatments which had a similar (P > 0.05) growth and feed utilization efficiency to those fed the control diet. The carcass compositions of catfish in all diets were similar (P > 0.05) and the liver histology of catfish fed any of the diets showed no alterations. The results obtained indicate that 50% of fish meal protein in practical catfish diets can be replaced with soybean flour and that catfish can effectively utilize supplemental methionine, thereby allowing up to 75% of the dietary fish meal protein to be replaced by soybean flour.     

Apparent digestibility of crude protein and gross energy in some plant and animal-based feedstuffs by Clarias isheriensis (Siluriformes: Clariidae) (Sydenham 1980)

Apparent digestibility coefficient (ACD) of dry matter, crude protein and gross energy of white fish meal, blood meal, poultry by-product meal, hydrolysed feather meal, shrimp head meal, meat and bone meal, soybean meal, cottonseed meal, peanut meal, yellow maize, corn starch, cassava meal, sorghum, rice bran and cocoa pod meal were determined for Clarias isheriensis (47.5–51.2 g) fed to satiation with diets containing each test feedstuff in a 30:70 mixture with a reference diet, and chromium oxide as an indicator using the dissection technique. ADC_protein values ranged from 50 to 93 % while ADC_energy ranged from 42 to 98 %. Protein and energy content of animal or plant feed-stuffs were equally digestible to C. isheriensis.     

Nutritive value of dried lactic acid fermented fish silage and soybean meal in dry diets for juvenile catfish, Clarias gariepinus (Burchell, 1822)

Dry diets containing either fish meal (C-FM) or dried fermented fish silage and soybean meal blend (1:1, ww⁻¹) (C-FS) as the sole protein source, were fed to triplicate groups of juvenile Clarias gariepinus (10.8 ± 0.3 g) at 5% body weight per day for 70 days. Catfish fed the C-FS diet showed reduced (P < 0.05) growth rate, feed conversion, protein efficiency and digestibility. Lower amounts of available amino acids in the C-FS diet resulted in inferior nutritive value for catfish growth than in the C-FM diet. Postprandial changes in plasma amino acids showed similar patterns in both diet treatments, but the maximal mean levels attained for the C-FS diet were correspondingly lower and occurred earlier than with the C-FM diet. There were no effects of feeding C-FS diet on the hepatosomatic index but carcass analysis showed that body protein deposition was lower (P < 0.05). Differences in haematocrit, haemoglobin content and liver histology were demonstrated but were not pathological. Lower digestible energy of C-FS diet also contributed to the poor performance of catfish in this treatment. Results of this study indicate that C. gariepinus cannot metabolize protein from co-dried fish silage as efficiently as fish meal protein when used as the sole dietary protein.     

Studies on the use of Clarias isheriensis Sydenham (Clariidae) as a predator in Tilapia guineensis Dumeril (Cichlidae) ponds

Quantitative evaluation of the dwarf African clariid catfish, Clarias isheriensis, as a predator to control excessive reproduction as well as to produce market-size substrate-breeding cichlid, Tikapia guineensis, was conducted in small earthen ponds at three Tikzpia/Charias stocking ratios (2:1, 5:1 and 10:1). During one roduction trial lastin 150 days, C. isheriensis reduced the T. guineensis fingerling population and edanced production of market-size (≥ 150 g) tilapias. Effective control of T. guineensis fingerling population occurred in the 2:1 stocking ratio treatment resulting in total-tilaia yiefd equivalent to about 4,548 kg ha^-1 yr^-1 and tilapia A^T Value (the percentage of market-size tilapia in the total tilapia opulation) of 96.2 at the preferred size with an average individual final weight of about 193 g. Differences in total tilapia yield, tilapia A^T values and average individual final weight between T. guineensis in the 5:1 and 10:1 stocking ratio treatments were not significant (p > 0.05). All of the mixed-culture treatments (Tilapia/Clarias) gave better feed conversion values than the control treatment (all Tilapia) (p ≤ 0.05).     

Food composition and digestive enzymes in the gut of pond-cultured Clarias isheriensis (Sydenham 1980), (Siluriformes: Clariidae)

Food composition, diestive enzyme distribution and activity in the gut of pond-cultured Clarias isheriensis were studied It had an omnivorous diet but fed mainly on plancon (particularly Cyanophyceae) and detritus. Qualitative determinations of digestive enzymes in the gut showed that it is capable of digesting carbohydrates, proteins and lipids in its diet. Carbohydrases (amylase, cellulase, maltase, salicinase, sucrase and trehalase) were detected and their activities restricted to the stomach, duodenum and ileum. The incidence of cellulase activity could be responsible for the capacity of this fish species to digest large quantities of Cyanophyceae present in the pond. Lower activity of proteases (chymotrypsin, pepsin and trypsin) and lipases were recorded. Enzyme activity was not recorded in either oesophagus or rectum. The relative distribution and activity of the various digestive enzymes were possibly induced by the nutritional requirements of this catfish species.