The Effect of Feeding Frequency on the Fin Condition in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Fin condition was assessed in the rainbow trout (Oncorhynchus mykiss) at an experimental recirculating facility using manual feeding 2 and 3 meals per day. Fin Index (FI) was used as an indicator of the find condition. Comparing the feeding frequencies 2 and 3 meals per day, a statistically significant difference was found (p < 0.05) for the FI of the pectoral, pelvic, anal, and caudal fins. For the 3 meals per day feeding frequency, a greater decrease of the FI was found compared to the feeding frequency 2 meals per day. In both pelvic fins the FI decreased by 53 %, in the caudal fins the FI decreased by 18 % and by 11 % in the anal fins, in the left pectoral fin the FI decreased by 6 % and by 12 % in the right one. Statistically significant difference was found between both pectoral fins for the feeding frequency of 3 meals per day. The left pectoral fin showed a FI higher by 8 % compared to the right one; the reason for the asymmetry being the water flow direction in the circular tanks. It follows from the results that in terms of fish welfare, it is more advisable to administer the feed 2 meals per day at maximum, in order to lower the risk of random biting by other individuals and to obtain a better fin condition.