Aquaculture Reports (Aug 2022)
Effects of carbon-nitrogen ratio manipulation on the growth performance, body composition and immunity of stinging catfish Heteropneustes fossilis in a biofloc-based culture system
Abstract
A 10-week indoor culture study was done to evaluate the effects of varying C/N ratios on growth performance, body composition, immunity, and haematology of stinging catfish Heteropneustes fossilis cultured in zero-water exchange culture tanks. Biofloc-based tanks with four levels of C/N ratio (12, 15, 18, 21) via the addition of carbohydrate referred to as ‘CN12′, ‘CN15', 'CN18' and 'CN21', and freshwater tanks operated with the facility of water exchange and without the addition of carbohydrate referred to as 'Control' (CN10). Fish (average weight 0.60 g) were stocked in 15 experimental tanks with 300 L water capacity and fed a commercial diet containing 30 % crude protein. The water quality parameters (pH, temperature, total ammonia nitrogen, nitrite nitrogen, dissolved oxygen, total suspended solids, and total dissolved solids) were monitored throughout the experiment. There was no significant (P > 0.05) difference among the treatments in the case of DO and temperature. The pH, total ammonia nitrogen, and nitrite nitrogen contents decreased with increasing C/N ratio, whereas the total dissolved solids and total suspended solids increased with gradually increasing the C/N ratio. Compared to the control, the treatment CN15 resulted in a 72 % and 34.4 % higher percent weight gain and specific growth rate, respectively. CN15 treatment resulted in improved feed utilization, as measured by feed conversion ratio (1.32 ± 0.07) and protein efficiency ratio (1.36 ± 0.10), which were 36.2 % lower and 54.5 % higher, respectively, than control. However, there were no differences in growth performance and feed utilization data between CN15 to CN21. Increasing the C/N ratio increased the body protein and ash contents and decreased the moisture and lipid contents compared to control. In the serum lysozyme test, the lysozyme value increased with a gradually increasing C/N ratio, and a better result was found in the CN15-CN21 treatments (15.58–15.74 µg ml−1) compared to the control (12.45 µg ml−1). At the end of the rearing period, fish were subjected to a challenge test with Aeromonas hydrophilla to determine the mortality rate where mortality was the lowest in CN15 treatment. Furthermore, increasing the C/N ratio from 15 to 21:1 showed better results for haemoglobin, white blood cells, red blood cells and hematocrit values. Overall, the manipulation of the C/N ratio from 15 to 21:1 revealed suitable for the feed utilization, growth performance, body composition, and immunity of stinging catfish. Therefore, maintaining a C/N ratio of 15:1 can be recommended for the culture of stinging catfish in the biofloc system.
