Abstract
This study compared three different fish species, striped catfish (Pangasius hypophthalmus), African catfish (Clarias gariepinus) and snakehead (Channa striata), regarding the effect of dietary macronutrient composition on: 1. the fillet yield and the fillet chemical composition; 2. the location of fat deposition within the body (fillet, liver, viscera or rest fraction). The selected species were studied for the development of net energy formulas, in three different studies. The design of these studies and especially the diet formulation were similar. Diets were formulated according to a 2 × 2 factorial design: with or without extra carbohydrates supplementation; and with or without extra fat supplementation. Fillet yield of striped catfish (P. hypophthalmus), African catfish (C. gariepinus) and snakehead (C. striata) was not affected by the dietary macronutrient composition. Fillet fat and protein contents were changed by the dietary macronutrient composition. In all compartments (liver, viscera, fillet and the rest fraction), both dietary fat and dietary carbohydrates levels increased the fat content. The response to dietary carbohydrates in snakehead, a lowering of fillet fat content, is opposite to the response in both catfish species. The distribution of the total amount of body fat over the different compartments, was not influenced by dietary carbohydrates level, but did depend on dietary fat level. Dietary fat supplementation led to relatively more fat in viscera and fillet but less fat was stored in the rest fraction. In striped catfish (P. hypophthalmus), African catfish (C. gariepinus) and snakehead (C. striata), most of the body fat is stored in the rest fraction (head, skin, subcutaneous fat, scales, bones and air bladders).
Highlights
The increasing use of carbohydrates and fat in fish feed (Craig et al, 2017; Ytrestøyl et al, 2015) increases the variability in dietary non-protein energy content
Averaged over the fish species studied in this study, the fillet yield was 31.8%, which is similar to values found in other studies on striped catfish (P. hypophthalmus) (Asemani et al, 2019; Da et al, 2012), African catfish (C. gariepinus) (Jantrarotai et al, 1998) and snakehead
In snakehead (C. striata) fed the low carbohydrates diets, fat supplementation increased the liver fat content by 139 g.kg− 1, but by only 75 g.kg− 1 in high carbohydrates diets (Supplementary table S3). These findings indicate the large differences in the location of fat deposition within the body, especially regarding the liver and viscera between snakehead (C. striata) and the other two fish species (African catfish - C. gariepinus and striped catfish - P. hypophthalmus), which are more omnivorous species
Summary
The increasing use of carbohydrates and fat in fish feed (Craig et al, 2017; Ytrestøyl et al, 2015) increases the variability in dietary non-protein energy content. Fish need energy for maintenance and growth. Energy can be acquired from either protein or non-protein sources, i.e., fat and carbohydrates. Because protein is the most expen sive macronutrient in fish feed, fish farmers prefer that dietary protein is used for protein growth and especially muscle growth rather than for energy. Mainly starch, is a cheaper energy source than fat. There are indications that too high inclusion levels of starch in fish feed may limit the growth performance of Nile tilapia (Oreochromis niloticus) (Schrama et al, 2012), barramundi (Lates calcarifer) (Glencross et al, 2017), snakehead (Channa striata) (Phan et al, 2021a,b) and rainbow trout (Oncorhynchus mykiss) (Groot et al, 2021)
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