Immunoreactivity of somatolactin (SL)-producing cells during larval development of Nile tilapia

Abstract

ABSTRACTIntroduction: A growing body of evidence confirmed the involvement of somatolactin (SL) in various physiological processes including the acid-base as well as calcium regulation, fat metabolism and osmoregulation. However, less is known about the immunoreactivity of SL- producing cells during developmental stages of Nile tilapia, Oreochromis niloticus. Aim of the work: The aim of the present work was to examine the immunoreactivity of SL-producing cells during different developmental larval stages of Nile tilapia, O. niloticus. Material and methods: We performed immunohistochemical technique using specific antibody against chum salmon SL to identify the anatomical distribution and change in the activity of SL-producing cells accompanied the different larval stages of Oreochromis niloticus, and study the possible involvement of this hormone in the early endocrine integration. Results: The present immunocytochemical assessments revealed a few and dispersed numbers of SL-positive cells at the first day after hatching. Moreover, we observed a gradual increase in the activity of SL-positive cells in the pituitary gland as reflected with the increased cell number and size as well as SL immunoreactivity concomitant with the continued larval development from the first day post-hatching onwards and reached the highest levels on day 35 post- hatching. In parallel to the advanced development of larvae, the number of SL-positive cells and the intensity of immunoreaction were clearly and gradually increased especially after the onset of exogenous feeding at 21-28 days post-hatching. Consequently, there is an obvious increase in both the larval body length and weight during the experimental period of rearing.Conclusion: The early appearance of SL-producing cells and the gradual changes in their immunoreactivity during development suggest crucial effects of this hormone in different physiological processes during larval rearing of O. niloticus especially in the period after yolk sac resorption.