The effect of feed mixtures with different protein and fat contents on production and chemical composition of the body of juvenile African catfish (Clarias gariepinus)

The African catfish Clarias gariepinus (Burchell, 1822) is considered as the most suitable species for intensive aquaculture in lukewarm waters due to its physiological characteristics and delicious meat. The objective of the paper was to compare the effect of available feeds for the culture of trout, catfish and carp on the growth rate and resultant chemical composition of the body in African catfish. The first experiment was conducted to test two feeds with different contents of proteins and fat (PA2 - declared nutrient content 47% proteins/12.5% fat, SA2 - 49/14) in fish with two initial weights (12.5 and 20.2 g). The performance parameters were positively influenced by feed with higher protein and fat content (SA2). The values of specific growth rate in experimental fish of both weight categories receiving this feed were higher in the first stage (20 days) by 2.3% (fish with lower initial weight - 3.06%/d) and by 2.9% (fish with higher initial weight - 3.86%/d) than in the other group (SGR 2.99 and 3.75%/d). But the differences in fish growth rate were not statistically significant. A similar trend was observed in the second stage of experiment (22 days). The use of feeds with higher protein and fat content (SA2) resulted in an increase in hepatosomatic index (HSI) in both smaller and larger fish (by 40.1% and 10.6%, respectively) in the first stage of experiment and in higher fat deposition in muscle (by 13.3 and 28.5%, resp,) at the end of experiment. The second experiment was carried out to test feeds for the production of trout (P2 - 42/13), catfish (S2 - 42/10) and carp (K2 - 30/14) in fish with initial weight 76.2 g. In the first stage of experiment (35 days), the best results were determined in fish receiving feed S2 (42/10 - SGR 1.44%/d, FCR 1.04), the worst in fish on diet K2 (30/14 - SGR 0.56%/d, FCR 3.32). Average individual weight of fish receiving feed K2 was demonstrably lower than in the other variants (P < 0.01) and was accompanied by the largest decrease in deposition of intramuscular fat (by 38.7% in females, by 29.6% in males) and visceral fat (by 60.6% in males, by 51.3% in females) in comparison with the values determined at the beginning of experiment. Tn the second stage of experiment (35 days), slower growth rate and lower feed conversion ratio were observed in the first (S2) and in the second variant (P2) while these parameters had higher values in the third variant when feed K2 was replaced by feed S2. The lower feeding intensity (1.5% of fish weight) resulted in further decrease in fat deposition and adipose tissue proportion in fish viscera in all variants.