Duration of stunting impacts compensatory growth and carcass quality of farmed milkfish, Chanos chanos (Forsskal, 1775) under field conditions

Abstract

An 18-months field trial was performed to explore the effect of duration of stunting on growth, digestive enzymes and carcass quality in Chanos chanos. Milkfish fry (weight of 1.25 ± 0.03 g and length of 5.53 ± 0.03 cm) were stocked in earthen ponds of 0.02 ha, in triplicate, for different duration of stunting, viz., 4 months (Treatment-1; T4), 8 months (Treatment-2; T8) and 12 months (Treatment-3; T12) and a normal seed (Control; C) separately. In the stunting phase, fish were stocked at higher stocking density (0.2 million/ha) and fed de-oiled rice bran at sub-optimal level. Post-stunting or re-feeding phase commenced immediately after completion of respective stunting duration and fish were reared for the rest of the period to complete the total rearing period of 18 months. In post-stunting, fish stocking density was adjusted to (5000 pieces/ha) and fed at an optimum level (3%). At the end of stunting phase, the study found a significant reduction in growth, survival, digestive enzymes activity, except protease in the T4 group, and carcass nutrients composition of stunted fish. However, in the initial phase of post-stunting, T8 group exhibited an elevated specific growth rate (5.00 ± 0.092%/day), body weight gain (80.82 ± 1.28 g), amylase (0.585 ± 0.021 U/mg protein), protease (5.48 ± 0.13 U/mg protein), and lipase activity (7.92 ± 0.32 U/mg protein). All stunted fish groups displayed a compensatory growth response in post-stunting, but a complete growth compensation was observed in T8 group, which resulted in better feed conversion ratio (3.03 ± 0.04) feed efficiency ratio (0.33 ± 0.01), protein efficiency ratio (1.91 ± 0.03), survival (91.38 ± 0.07%) and digestive enzyme activities. Similarly, at the end of post-stunting, carcass analysis revealed a complete restoration of nutrients in stunted fish and significantly higher protein content in T8 group. Further, the study found lower meat and higher bone contents in normally reared fish than the post-stunted fish which revealed the carcass quality improvement in post-stunted fish thus indicates superiority of the stunting process over normal rearing. Overall, the study suggests that stunting of milkfish, for 8 months (T8), positively affects its growth, survival, digestive enzyme activities and carcass quality which in turn, shall help to overcome the contemporary challenges in milkfish culture.