Effects of dietary protein level on growth, histology and digestive enzyme activities of ornamental fish Ancistrus cirrhosus

Regardless of the developmental stage of the cultured organism, proper nutritional care is essential. A significant number of aquacultural species rely on protein as their main energy source and protein feeds sold in the ornamental market are formulated with widely varying protein inclusion levels. As Ancistrus cirrhosus is one of the most popular ornamental fish species, this study aimed to determine the effects of different protein levels on growth, digestive enzyme activities and liver and intestinal histopathology. Therefore, 450 fry (98.5 ± 3.1 mg [mean ± SE]), 5–6 weeks old, were fed six different experimental diets containing 30%, 35%, 40%, 45%, 50% and 55% crude protein in triplicate groups for 60 days. The results demonstrated that no significant differences were observed in the final lengths, whole‐body protein levels, body condition indices and lipase and alkaline phosphatase activities of fish between groups. The fish fed with a 40% protein diet differed positively from other experimental groups in terms of final weight, FCR, SGR, proteolytic enzyme activities and histopathological findings. Lower proteolytic activity was ascertained in fish fed feed containing lower levels of protein (30%, 35%) and increased histopathological defects in the intestine and liver of fish fed feed containing over 40% protein (45%, 50% and 55%). Based on our results, a diet with a 40% protein level is most beneficial for the rearing of A. cirrhosus fry. Further research is required to determine optimal ratios, which are predicted to be between 35 and 40.