Viviparity and embryonic adaptations in the teleost Clinus superciliosus

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Abstract
Autoradiographic studies reveal that embryos of Clinus superciliosus absorb nutrients from the embryotrophe secreted by the follicular wall. The embryonic structure active in nutrient absorption is the epidermis including that of the fins and the gut. Absorption initially takes place mainly through the epidermis, with the pericardial and yolk-sac areas being the most active. In prepartum embryos most of the nutrient absorption takes place through the gut. Embryonic exchange surfaces of C. superciliosus were studied by both light and scanning electron microscopy. Changes in absorptive activity during embryonic development were mirrored by changes in surface topography and intestinal anatomy. The relative surface area of early embryos is greatly increased by numerous epidermal macroridges, which are particularly abundant in the pericardial and yolk-sac areas, as well as by epidermal microvilli. With increase in embryo size, the macroridges are reduced in number, and finally disappear just prior to birth. However, the mid- and hind-gut areas hypertrophy during gestation. It is suggested that this hypertrophy compensates for the progressive reduction in epidermal surface area during development and that such reduction in surface area is a possible osmotic adaptation.