Usefulness of histological criteria for assessing the adequacy of diets for Panulirus japonicus phyllosoma larvae

Abstract

Mass seed production depends a great deal on the development of adequate artificial diets, which in turn depends on the development of methods to speedily and reliably assess the nutritional value of experimental diets. This study examined the sensitivity of light histological and ultrastructural criteria to detect differences in the nutritional value of diets for the Japanese spiny lobster, Panulirus japonicus (V. Siebold), phyllosoma larvae. The acceptability of diets, the apparent absorption of lipids and carbohydrates by the midgut gland cells, and the characteristics of various cell types were determined in 43-, 106- and 143-day-old intermoult phyllosoma fed diets of Mytilus edulis (L.) ovary alone (MO) or in combination with Anemia (MO+AR), which so far have given the best results in terms of growth and percentage of metamorphosis into puerulus, and two other diets considered less efficient, viz. Mytilus edulis testis (MT) and Artemia (AR). Acceptability of all diets attained 100% within 10 min of feeding as revealed by observation through the semitransparent cuticle of the larvae. Histological examination of larvae that ingested comparable amounts of food revealed pronounced variation in the absorption of lipids and carbohydrates by the midgut gland cells (AR<MT≤MO+ARp<MO), in the size and ultrastructure of the midgut gland epithelial cells (AR<MT<MO+AR<MO), in the number, size, and electron-dense body content of the haemocytes (AR<MT≤MO+ARp<MO), and in the size of cells lining the midgut gland tubules (AR≤MT≤MO+AR<MO). Growth and survival followed the order MT≤AR<MO+AR≤MO with maximum survival rates around 25–35% on the more efficient diets. Thus, phyllosoma fed on each diet presented a distinctive set of histological characteristics. Moreover, histological variation between diets was detected earlier than, and yet correlated strongly with, the results on growth and survival. This suggests that histological criteria constitute a practical means for the preliminary assessment of the acceptability and nutritional value of diets for the Japanese spiny lobster.