Introduction
Although fish meal (FM) has been considered the most preferred protein source in aquafeeds, intense focus has been given on the reduction and/or elimination of FM protein over the past several decades due to its high price and insufficient supply. Shark by-catch muscle meal (SM), which has been otherwise wasted away, was used to replace fishmeal (FM) in the diet of juvenile Japanese yellowtail, Seriola quinqueradiata to investigate its effect on growth and phosphorus (P) loading to the ecosystem.
Materials and methods
The control diet (C) was composed of FM as protein source, and 25%, 50%, 75% and 100% of FM protein from diet C was replaced by SM to formulate diets SM25, SM50, SM75 and SM100, respectively. A group of 25 fish (mean weight 18.01 ± 0.09 g) were stocked into each 500 L tank in triplicate for each treatment, fed two times daily until apparent satiation for 6 weeks. Feces collection trial was carried out by using chromic oxide as an inert marker after finishing the growth trial. The photoperiod was set to 12 h of light (07:00-19.00) and 12 h of dark during the whole rearing period. The UV-treated filtered seawater was supplied at 7 L/min per tank, and water temperature and dissolved oxygen levels during the test period were 26.1 ± 1.0°C and 6.4 ± 0.7 mg/l, respectively. During the test period, the bottom was cleaned with a siphon every day at 11:00, and dead fish were counted and weighed if mortalities were observed.
Results and conclusion
There were no significant differences in growth parameters among fish fed with diets C, SM25, SM50 and SM75 (P < 0.05, Tukey’s test), though SM100 produced significantly lower performance compared to all diets (P > 0.05). Moreover, there was a strong negative (R2 = 0.964) and positive (R2 = 0.904) linear correlation between daily feeding rate and SM, and between feed efficiency and SM levels in diets, respectively. Although there were no significant differences in protein and fat productive value among the treatments, P productive value was significantly increased with increasing levels of SM in diets, resulting in a significant lower P loading from SM-based diets (P < 0.05). There were no significant differences in plasma levels of total protein, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and total cholesterol (P > 0.05); however, plasma levels of triglyceride, blood urea nitrogen and ammonia were significantly increased in fish fed with diet SM100 compared to the control group (P < 0.05). In conclusion, the results suggest that 75% of FM protein can be replaced by SM without compromising the growth performance and health condition, and that a significant ecological benefit can be achieved by reducing P loading from SM-based diet. From an economic standpoint of view, the application of SM would help to reduce dependency on high cost and scarce FM.