Effects of Feeding Level on Circulus Formation on Scales of Young Sockeye Salmon (Oncorhynchus nerka)

Abstract

Feeding level exerted a significant influence on scale growth of young sockeye salmon (Oncorhynchus nerka) maintained for 2 months at a temperature of 13.98 ± 0.29 C and a constant photoperiod of 12 hr light and dark. The number and spacing of circuli, scale radius, and length and weight of the fish were all correlated with the feeding level. Two checks at most were observed on scales of fish in the experimental populations. At midpoint of the experiment, incidence of a first check was highest among fish that had been held at a high feeding level. At the end of the experiment a second check was apparent only on scales of fish that had the feeding levels raised at midpoint of the experiment. There were significant correlations between the nucleus radius of the scale and length and weight of the fish.