Availability of fisheries by-product materials with cadmium removal treatment as a feed ingredient for fingerling black rockfish Sebastes schlegeli

Squid liver and scallop-mid gut glands, which are generated and discarded as waste from the Japanese common squid and Japanese scallop, are rich in amino acids and lipids. However, the squid liver and scallop mid-gut glands contain cadmium (Cd) which is generally known as a harmful heavy metal for human health. Hirama et al. recently studied a technique for removal of Cd from squid viscera and scallop mid-gut glands and confirmed the efficacy of the acid leaching and electrolysis method to produce the fisheries by-product materials (meal and extract) with Cd removal treatment as a feed ingredient for cultured fish. So far we have evaluated the nutritional value of squid viscera meal with Cd removal treatment (dCSVM), which contained 1.5-2.0 mg/kg Cd, as an alternative protein source to sardine meal in diets for fingerling black rockfish Sebastes schlegeli. In our study, it was clearly demonstrated that dCSVM with good protein digestibility could be substituted for 60% of sardine meal in diets for fingerling black rockfish without growth retardation, poor palatability and the problem of Cd accumulation. We suggested that dCSVM was superior to commercial squid viscera meal without Cd removal treatment (CSVM) as a high-quality feed ingredient for black rockfish based on the heavy metal accumulation in fish tissues. Recently, we are investigating availability of mid-gut glands extract with Cd removal treatment (dCSMGE) as a feed ingredient for fingerling black rockfish. In the recent study, we found that weight gain, specific growth rate, and feed efficiency of fish fed the diet containing dCSMGE at 2% were significantly higher than those of the control. Furthermore, we confirmed that test diets containing dCSMGE was safe in terms of accumulation of Cd. These results demonstrate that proper inclusion of dCSVM and dCSMGE is effective for the improvement of feed quality in practical diets for fingerling black rockfish.