The histochemical patterns of leucine naphthylamidase (LNAase) and alkaline phosphatase (AP) activity have been studied in the developing alimentary tracts of embryos (20 mm. - 200 mm.) of the skate Raja binoculata Girard. The enzyme(s) LNAase was found only in the spiral valve mucosae possessing elongated adult-like villi. The activity level increases with the growth of the embryo. The enzyme(s) is probably not related to differentiative events of the spiral valve but rather a manifestation of a particular stage of functional differentiation. Several possible physiological functions of the enzyme(s) are discussed. The enzyme AP had a more general distribution. It was found in many differentiating regions of the digestive tract. Activity levels which were generally high in undifferentiated mesenchymal tissue, decreased with further differentiation in some tissues. In other regions where AP remained in the adult, the enzyme accumulated with advancing differentiation. The significance of AP in the various localizations is discussed. AP isozyme patterns during alimentary tract development were studied using polyacrylamide gel electrophoresis. These data were correlated with the histochemical localization of the enzyme activity. It appears that new molecular forms of AP arise during gut differentiation. The relationship between AP and differentiation is discussed and AP is related to specific function where applicable. / Science, Faculty of / Zoology, Department of / Graduate

Thèse de doctorat : Zoologie : Faculté des sciences de Paris : 1847. / Titre provenant de l'écran-titre.

The systematics of the Rajidae (skates) of southern Africa are revised, with a view to clearing up the confusion which now exists, and to forming a reliable basis for future biological studies. To date, some 150 - 160 species have been described for the genus Raja alone. The existing confusion probably results from the sexual dimorphism which occurs within the species and variation in form with growth. Modern methods advocate the use of characters, other than external features, the most reliable being the clasper anatomy, neurocranial structure and vertebral count, and these principles have been applied in the present revision.

Members of the family Rajidae are common components of the demersal trawl fishery, contributing around 1% to the total catch. However, apart from a single species all South African rajids are currently discarded. With demands for new protein sources ever-increasing, it is possible that currently underutilised species, such as the skates will be utilized to a greater extent. Raja wallacei and R.pullopunctata are common trawler by-catch species, ranging along most of the South African coast. The current study allred to further knowledge on the population biology of both species through age and growth, reproductive and feeding studies. The study also allred to assess whether any of the South African skate species show the potential for utilization as a food source. Band counts of vertebral centra were used to determine growth parameters and generate growth curves for males and females of both species. Growth was significantly different between the sexes. In both cases, females grew slower than males but reached a greater asymptotic disc width. As with other elasmobranchs, R.wallacei and R.pullopunctata are long-lived and slow growing. As with all other skates, the study species are oviparous laying large, yolked eggs in tough, leathery cases on the sea bed. The onset of maturity occurs at a large size (approximately 400mm disc width (10-11 years of age) for R.wallacei and 600mm disc width (12-13 years of age) for Rpullopunctata) and is very rapid. The oldest R.wallacei and R.pullopunctata observed were 16 and 18 years of age, respectively. No distinct breeding season was determined and no nursery areas were observed. A large proportion of individuals, especially R.pullopunctata was immature. Both species fed primarily on crustaceans and teleosts with an ontogenetic shift in diet from mysids, amphipods, isopods and bregmatocerids to larger Gnathophis sp., Mursia cristimanus and carid shrimps. Large discrepancies were seen in the diet of animals spatially, temporally and between research and commercially-caught animals. Disc-width frequency data was limited but suggested that both species show preference for depths of 100-300m. Size distribution did not appear to be affected by depth, although the data set was limited. A paucity of large individuals in the catch may indicate that stocks are suffering from growth overfishing by trawling operations. Historical and observer data showed that although skates are common components of the by-catch, the potential for greater use is limited. The biscuit skate, R.straeleni, on the west coast is the only species that could be better utilized. If skates are treated as a single group the potential is increased but this causes problems in assessing stocks.

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