Effects of feeding levels on growth performance, feed utilization, body composition and apparent digestibility coefficients of nutrients for juvenile Chinese sucker, Myxocyprinus asiaticus

An experiment was conducted to determine effects of feeding levels on growth performance, feed utilization, nutrient deposition, body composition and apparent digestibility coefficients (ADCs) of nutrients for juvenile Chinese sucker (initial weight, 11.77 +/- 0.22 g). Chinese sucker were fed a practical diet from 0% (starvation) to 4.0% (at 0.5% increments) body weight (bw) day-1 for 8 weeks. The results showed that growth performance, feed utilization, nutrient deposition, body composition and ADCs of dry matter, protein and energy were significantly (P < 0.05) affected by feeding levels. Survival was the lowest for the starvation group. Final mean body weight, growth rate, thermal-unit growth coefficient (TGC) increased with feeding rate from 0% to 3.0% bw day-1 (P < 0.05) and showed no significant differences above the level (P > 0.05). Feed conversion rate was significantly lower at a feeding level of 2.5% bw day-1 than above and below the level (P < 0.05). Protein efficiency ratio was markedly highest at the 2.5% bw day-1 ration level (P < 0.05). Fish fed at the feeding level (1.0% bw day-1), which represented a maintenance ration (energy gain was less than 2.27 kJ fish-1 day-1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. Lipid contents of whole body, muscle and liver increased with increasing feeding rates from 0.5% to 3.0% bw day-1 and showed no significant differences above the level (P > 0.05). Protein contents of whole-body composition increased with feeding rate from 0.5 to 3.0% bw day-1 (P < 0.05) and showed no significant differences above the level (P > 0.05), whereas muscle and liver remained relatively stable with the different ration amount with the exception of fish fed a ration of 0.5% bw day-1, at which Chinese sucker possessed significantly lower body protein concentration (P < 0.05). The ADCs of dry matter, protein and energy decreased with increasing feeding levels from 0.5% to 3.0% bw day-1 and then remained relatively constant over the level. Based on the broken-line regression analysis using WG data, the optimum and maintenance feeding levels for Chinese sucker were 3.10% bw day-1 and 0.45% bw day-1 respectively.