Optimal dietary carbohydrate to lipid ratio in African catfish Clarias gariepinus (Burchell 1822) |
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| Authors: | M Z Ali K Jauncey |
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| Institution: | (1) Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, Scotland, UK;(2) Present address: Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh, 2201, Bangladesh |
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| Abstract: | An 8-week feeding trial was conducted in a recycling water system at 28 ±1°C to investigate carbohydrate to lipid ratio (CHO:L ratio) in African catfish Clarias gariepinus (12.32±0.04g). Five isonitrogenous (40% crude protein) and isoenergetic (20kJg–1 gross energy (GE)) fishmeal based diets with varying carbohydrate to lipid (CHO:L g/g) ratios of 0.74, 1.13, 1.66, 2.47 and 3.42 for diets 1–5, were tested, respectively. The diets containing a fixed protein to energy ratio (P:E ratio) of 20-mg proteinkJ–1 GE were fed to triplicate groups of 20 fish (per 30-L tank). Fish were fed 5% of their body weight per day adjusted fortnightly. Diet 1, containing 14% carbohydrate and 21% lipids with a CHO:L ratio of 0.74 produced the poorest (P<0.05) growth rates, feed and protein efficiency. Increasing carbohydrate content in the diets to 27% concomitant with a reduction in lipid content to 16% with a CHO:L ration of 1.66 of diet 3 significantly improved (P<0.05) growth rates, feed and protein efficiency. A further increase in dietary carbohydrate up to 38% and a decrease in lipids levels to 11% with a CHO:L ratio ranging from 1.66 to 3.42 (diet 3 – 5) did not significantly improve the fish performance. Apparent net protein utilisation (ANPU) of fish fed diet 4 was higher (P<0.05) than for diets 1–3 but did not differ from diet 5. Higher lipid deposition (P<0.05) in whole body and liver were observed with decreasing dietary CHO:L ratios as increasing lipid levels. Whole body protein and liver glycogen content, digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying CHO:L diets did not show any discernible changes among the dietary treatments. However intestinal  -amylase activity increased (P<0.05) with increasing dietary carbohydrate levels. This study revealed that African catfish can perform equally well on diets containing carbohydrate ranging from 27 to 38% of the diet, with lipid content ranging from 16 to 11% or at CHO:Lg/g ratio of 1.7–3.4. |
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| Keywords: | African catfish (Clarias gariepinus) Carbohydrate to lipid ratio Digestive enzymes Protein utilisation |
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