An Ultrastructure Study of Diet‐Related Changes in Epithelial Tissue of Hybrid Striped Bass Larvae

Abstract

This study characterized the ultrastructure of normal epidermal and gastrointestinal epithelial cells of larval hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis) that were fed live prey (brine shrimp Artemia spp. nauplii) or an artificial dry diet. Scanning electron microscopy of larvae that were given live feed revealed normal epidermal cells with microridge structures and proliferation of neuromasts along the lateral line. Cell junctions had double microridge structures. Transmission electron microscopy of the gut showed keratinized epithelial cells with underlying mucous cells in the foregut, while the midgut was characterized by columnar epithelial cells with extensive pinocytotic activity. The hindgut had columnar epithelial cells with centrally located nuclei, regularly spaced microvilli, and numerous tubular mitochondria surrounded by rough endoplasmic reticulum. Larvae that received live feed reached metamorphosis by 27 d posthatch (dph), and clearly identifiable gastric glands were present. Larvae that were given the artificial diet did not develop; both epidermal and gastrointestinal cells showed apparent osmotic stress by 10 dph, and the condition worsened through 24 dph. Stress was indicated by loss of microridges in epidermal cells and eventual necrosis. Increased keratinization and reduced pinocytotic activity were observed in midgut cells, whereas hindgut epithelial cells showed dissociation of the rough endoplasmic reticulum and reduced numbers of mitochondria. However, tight cell junctions, desmosomes, and double microridges at cell junctions persisted.