Experimental Impoundments of Prespawning Pacific Herring (Clupea harengus pallasi): Effects of Feeding and Density on Maturation, Growth, and Proximate Analysis

Abstract

Approximately 3 mo before spawning, Pacific herring (Clupea harengus pallasi) were captured and transferred to experimental netpens and subjected to different holding conditions: high, medium, and low densities; with and without covers; and fed and not fed. Mortality during impoundment was low. There were no detectable effects of density or cover, but feeding accelerated spawning time and promoted gonadal growth. Fed fish had significantly higher somatic weights, gonad weights, and condition factors and significantly lower gonosomale indices than unfed fish. Water content increased in all fish from about 70%, at the beginning, to about 75% when the fish were ripe. Consequently, total body weight increased in all females, and somatic weight decreased, but the decrease was feast in the fed fish. No significant differences in the percentages of total protein and ash in the carcass were found during impoundment, but the levels of fat and free fatty acids showed a progressive decrease. Glycogen levels in the muscle and liver were higher in fed herring. Oocyte maturation was normal. Preovulatory atresia of vitellogenic oocytes was observed in all groups. Egg diameters of fed females were slightly larger than those of unfed fish. The evidence for winter feeding in Pacific herring is evaluated.