Epidermis differentiation in Salmo irideus Gilb. development [Translation from: Archo ital.Anat.Embriol. 76, 19-30, 1971]

Recent histochemical and histophysiological research on the skin of fish has posed interesting problems both with regard to the presence of specialized types of cell and with regard to the function of this organ. The present paper intends to study the development and the functional differentiation of the trout's skin, both from the histomorphological and the histochemical point of view. The skin of Salmonids is devoid of specialized cells; the granular cells of Petromyzonti, the serous cells of Selacii and the clavate cells described in many other teleosts and it lacks keratin. As such it can be considered a good working model which can be used to show the eventual histomorphological and histochemical changes occurring both in the transformation from the endovular to the aqueous environment. Histomorphological observations were carried out demonstrate the great structural simplicity of the trout's skin at all stages. The article concludes that glycogen increases greatly when the epidermis thickens and therefore when it becomes necessary to guarantee resistance, amongst which is a support mechanism.

Sexual differentiation and gonad development in striped mullet (Mugil cephalus L.) from South Carolina estuaries*

This study examined the sexual differentiation and reproductive dynamics of striped mullet (Mugil cephalus L.) in the estuaries of South Carolina. A total of 16,464 specimens were captured during the study and histological examination of sex and maturity was performed on a subsample of 3670 fish. Striped mullet were sexually undifferentiated for the first 12 months, began differentiation at 13 months, and were 90% fully differentiated by 15 to 19 months of age and 225 mm total length (TL). The defining morphological characteristics for differentiating males was the elongation of the protogonial germ tissue in a corradiating pattern towards the center of the lobe, the development of primary and secondary ducts, and the lack of any recognizable ovarian wall structure. The defining female characteristics were the formation of protogonial germ tissue into spherical germ cell nests, separation of a tissue layer from the outer epithelial layer of the lobe-forming ovarian walls, a tissue bud growing from the suspensory tissue that helped form the ovary wall, and the proliferation of oogonia and oocytes. Sexual maturation in male striped mullet first occurred at 1 year and 248 mm TL and 100% maturity occurred at age 2 and 300 mm TL. Female striped mullet first matured at 2 years and 291 mm total length and 100% maturity occurred at 400 mm TL and age 4. Because of the open ocean spawning behavior of striped mullet, all stages of maturity were observed in males and females except for functionally mature females with hydrated oocytes. The spawning season for striped mullet recruiting to South Carolina estuaries lasts from October to April; the majority of spawning activity, however, occurs from November to January. Ovarian atresia was observed to have four distinct phases. This study presents morpholog ical analysis of reproductive ontogeny in relation to size and age in South Carolina striped mullet. Because of the length of the undifferentiated gonad stage in juvenile striped mullet, previous studies have proposed the possibility of protandric hermaphrodism in this species. The results of our study indicate that striped mullet are gonochoristic but capable of exhibiting nonfunctional hermaphroditic characteristics in differentiated mature gonads.