Histological criteria for diagnosing the starving condition in early post yolk sac larvae of the northern anchovy, Engraulis mordax Girard

Abstract

The identification of fish larvae that are in starving condition in plankton samples would be a valuable aid in estimating early mortality rates of populations in the sea. Histological criteria are given for determining the degree of starvation-induced emaciation, with an indication of its relevance to mortality, for larvae of the northern anchovy, Engraulis mordax Girard. Larvae were reared with and without food to age 9 days, i.e., beyond the point of yolk absorption. Eleven histological characteristics were each graded on scales of poor, intermediate or good, depending variously on texture, shape and fullness of nuclei, cytoplasm, extracellular substance, and cellular products and storage material. Grades varied with food deprivation, so that increasing emaciation may be estimated from histological variables. Distribution of the grades also paralleled trends in survival and length, indicating that degree of emaciation reflects the probability of survival. The histological variables that best classified larvae as severely emaciated, moderately emaciated, or robust in a stepwise discriminant analysis were pancreas condition, trunk muscle fiber separation, intermuscular tissue, and liver cytoplasm. The discriminant analysis suggests that an average of grades for three or four characteristics is sufficient for determining the state of emaciation of a larva.