Influence of some environmental variables on the ascorbic acid status of mullet, Mugil cephalus L., tissues

Abstract

The seasonal fluctuations in the ascorbic acid (AsA) and ascorbic acid 2-sulphate (AsA 2-sulphate) content of mullet, Mugil cephalus, tissues were examined. Ascorbic acid concentrations in brain, gill and hepatic tissues showed seasonal changes, but the pattern of AsA fluctuations in each tissue differed. The AsA content of mullet brains decreased during the summer, whereas hepatic AsA concentrations increased during this period and were maximal by the end of June. Hepatic AsA reserves declined after environmental water temperatures dropped below 18" C and reached a minimum (20 pg g-') by the end of January. Greatest fluctuations in AsA content occurred in gill tissues, which had a four-fold range of tissue concentrations. There were also seasonal changes in the AsA 2-sulphate content of brain and hepatic tissues. These differences among mullet tissues in the seasonal patterns of AsA content may be due to diverse effects of environmental variables on tissue AsA reserves. The ability of hepatic and renal tissues of mullet and several other teleost species to synthesize AsA was also investigated. L-gulonolactone oxidase activity was detected in all the species examined, but in all cases the biosynthetic capacity was less than a seventh that in goldfish, Carassius aurafus, livers. Mullet appear to have only a limited capacity to synthesize AsA.

Biosynthesis of ascorbic acid by extant actinopterygians

“…All non-teleost actinopterygians under study here possessed GLO activity and thus are capable of de novo synthesis of AA. On the basis of improved enzyme activity assays and immunological tests, present data refute earlier reports that the common carp and the goldfish possess GLO Yamamoto et al, 1978;Soliman et al, 1985;Thomas et al, 1985). On the contrary the present investigation supports the hypothesis that present-day teleosts lack GLO (Fig.…”

“…However, the character distribution in extant fishes is not fully elucidated. Since controversial reports claimed that fishes cannot synthesize AA (Nandi et al, 1997) or that some teleosts have GLO activity Yamamoto et al, 1978;Soliman et al, 1985;Thomas et al, 1985), confirming existing but *Author to whom correspondence should be addressed. Tel.…”

Variation of vitamin C in some common species of marine plankton

“…3A, C:t = 100 to 110 h), demonstrating further a direct link between food uptake and incorporation of vitamin C by copepods. These conclusions, based on only a few observations, should be ultimately tested through enzymatic assays, similar to those performed on rat and fish (Loewus et al 1960, Chatterjee 1973, Thomas et al 1985, Koshizaka et al 1988. Minimum concentrations of vitamin C in both Calanus helgolandicus and Acartia clausi starved in the laboratory were close to values recorded in naturally occurring copepods during winter, or on stations where the concentration of chlorophyll a in seawater was <0.5 yg l-'.…”

Variation in Vitamin C content of sprat larvae (Sprattus sprattus) in the Irish Sea

“…blood, kidney) are a good index of the nutritional status of fishes (Mahajan and Agrawal 1979). Although a significant biosynthetic ability has been found in several species of Cypriniformes (Yamamoto et al 1978, Thomas et al 1985, the capability to synthesize Vitamin C has been lost (Chatterjee et al 1975) or is weak in most fish species (Soliman et al 1986). This incapacity is due to a lack of L-gulonoiactone oxidase catalysing the conversion of L-gulono-7-1actone to ascorbic acid (Wilson 1973).…”