The influence of dietary protein concentration on digestive enzyme activities, growth, and body composition in juvenile bullseye snakehead (Channa marulius)

The bullseye snakehead (Channa marulius) is considered as an affordable and robust freshwater fish for farming in Asia. However, there is limited knowledge on the species’ full nutritional requirements to date with extensive gaps in our knowledge and particularly in precision aspects of protein requirements. Therefore, a three-month feeding trial was conducted under semi-intensive farming conditions to determine the protein requirement of bullseye snakehead using test diets containing 40 (P40), 45 (P45), 50 (P50), and 55% (P55) crude protein levels. The growth performance results revealed that the 55% dietary protein group (P55) had the highest final mean weight (14.09 g fish(-1)), and net weight gain (12.82 g fish(-1)). When compared to other dietary treatments, the final weight (R(2) = 0.921), and weight gain (R(2) = 0.913), displayed a linear increasing trend as dietary protein is raised. The lowest FCR was observed in 50% (1.94±0.01) and 55% (1.97±0.01) CP diet groups compared to dietary treatments. Further analysis has shown that the body protein content also significantly increased as dietary protein was raised to 55%. Although, a reverse trend was found in body lipid levels with increasing protein in the diet. The incremental dietary protein also elevated proximal intestinal protease activity but decreased amylase and lipase activity. The overall essential and non-essential amino acids levels of snakehead fillet muscle reflected an increase in dietary protein. Overall, this study has shown that the fish fed a diet with 55% crude protein attained the highest growth performance and nutrient profile of the whole fish when compared to other dietary treatments tested. It would appear we did not obtain the maximum potential for growth under the present experimental conditions due to the upper protein constraint of 55% in the diet. Further quantitative studies are suggested.