Effects of total replacement of fish oil by pork lard or rapeseed oil and recovery by a fish oil finishing diet on growth, health and fish quality of gibel carp (Carassius auratus gibelio)

An 84-day growth trial was designed to investigate effects of dietary replacements fish oil with pork lard (PL) or rapeseed oil (RO) on growth and quality of gibel carp (Carassius auratus gibelio var. CAS III) (initial body weight: 158.2 +/- 0.2g), and responses of the fish refed fish oil (FO) diet. Three isonitrogenous (crude protein: 30%) and isolipid (crude lipid: 10%) diets were formulated containing 7.73% FO, PL or RO. Five experimental treatments including FO group (FO), PL group (PL), RO group (RO), group fed PL for 42days and refed FO for 42days (PL+rFO), RO and refed FO group (RO+rFO) was tested. At the end of first 42days, the fish fed PL and RO had higher mortality than that of the control (P>0.05). At the end of whole experiment, fish fed PL and RO showed higher plasma cortisol than FO fish (P<0.05). RO+rFO fish showed higher lysozyme activity than RO fish (P<0.05). Fish growth and feed utilization, composition of whole body and muscle, free amino acids, texture, off-flavour substances or sensory attributes were not affected by dietary treatments (P>0.05). PL and RO diet decreased muscle EPA, DHA and n-3/n-6 ratio (P<0.05), while FO-refeeding had recovery effect. It can be concluded that the replacement of FO by PL and RO does not affect the growth, feed utilization or fish tasting quality in gibel carp. Fish muscle fatty acids modified by dietary PL and RO can be recovered by refeeding with FO diet.