UC San Diego

Teleost fishes maintain homeostasis through the action of ionocytes, epithelial cells specialized for osmoregulation, acid-base regulation, and ammonia excretion, among other functions. While studied extensively in adult fishes, much less is known about ionocytes and their function in marine teleost larvae. The goal of this thesis is to track the ontogenetic changes in number, size, distribution, and morphology of ionocytes in skin and gills of larval White Seabass (Atractoscion nobilis) ranging from 1-32 days post-hatch (2.6 to 16.4 mm body length). Immunostaining of ionocytes revealed a stark increase in ionocyte number and density, and a decrease in ionocyte size throughout the sample period. Relative ionocyte area, a proxy for ion excretion across the skin, was calculated revealing a decrease in cutaneous ion excretion prior to the timing of notochord flexion. During this period, the branchial structures became increasingly developed and were highly abundant in ionocytes, suggesting they are taking on a large portion of the ionoregulatory role. Scanning electron microscopy revealed several different apical morphologies in a 32 DPH larva, and confocal scanning laser microscopy revealed the presence of ionocyte in the skin of a juvenile White Seabass. This is the first study to provide high temporal resolution tracking of the ontogenetic changes of ionocytes in larval White Seabass, who were selected due to their high socio-economic value and for the increasing demand for research to aid in the wild stock enhancement aquaculture program operated by Hubbs SeaWorld Research Institute (San Diego).