EFFECT OF TRIIODOTHYRONINE ON STOMACH FORMATION AND PIGMENTATION IN LARVAL STRIPED BASS (MORONE-SAXATILIS)

We previously reported that ambient T-3 was taken up by larval striped bass (Morone saxatilis) in a dose-dependent manner, and, at 100 ppb T -3-salt in 5 ppt seawater, ambient T-3 retarded the growth of the fish . Here we examined the effects of T-3 on the histogenesis of the stoma ch and on pigmentation of larval striped bass. Striped bass larvae wer e raised in 0, 1, 10, or 100 ppb T-3-Na salt in 5 ppt seawater beginni ng at 16 days after hatching (dah) and sampled after 1 or 2 weeks of t reatment. Between ages 23 dah and 30 dah, the muscular layer of the st omach thickened in all groups, and, at both times, the stomachs of fis h treated with the highest dose of T-3 had a significantly thicker mus cular layer than stomachs of untreated fish. The length of the fundic stomach doubled between sampling times in the control fish; this devel opmental change was promoted by the lowest dose after 1 week exposure, but after 2 weeks this and the development of the gastric blind-sac w ere significantly inhibited in fish treated with the medium and high c oncentrations. The fundic region of the stomach of all fish examined a t each sampling time (n = 48) contained gastric glands in which pepsin ogen was immunolocalized; however, because of the smaller size of the fundic region and the absence of the gastric blind-sac, many fewer gas tric glands were detected in fish treated with the two higher concentr ations. Somatic pigmentation increased between 23 dah and 30 dah and w as also stimulated by exogenous T-3 in a dose-dependent manner within 1 week. After 2 weeks of treatment, only fish exposed to 100 ppb T-3-N a salt were more pigmented than the control fish. Although development of pigmentation and the muscular wall of the stomach were accelerated by T-3, effects of treatment on differentiation and possibly function ing of the fundic region were more complex and possibly detrimental. ( C) 1998 Wiley-Liss, Inc.