An annual cycle of vitellogenesis in the elasmobranch Scyliorhinus canicula

Abstract

Plasma vitellogenin synthesis in adult female Scyliorhinus canicula L. continued throughout the year but the rate of synthesis was significantly lower between March and August than during the rest of the year. The hepatosomatic index (liver weight as percentage of body weight) underwent annual variation in both sexes but this variation was considerably more pronounced in the female. Increase in hepatosomatic index in the female was accompanied by increase in the percentage of lipid in the liver and was largely caused by increase in the total lipid content of the liver. Comparison of livers of males and females showed that the percentage of lipid was not significantly different while the percentage of solids insoluble in water and organic solvents was greater in the female. Oviposition, as indicated by the percentage of females with eggs in the oviducts, continued throughout the year, reaching a minimum in September-October. Between July and October, parameters associated with vitellogenesis began recovery from their respective annual minima in the following order: plasma oestradiol level, hepatosomatic index, rate of synthesis of plasma vitellogenin, gonosomatic index, plasma vitellogenin level, rate of oviposition. I N T R O D U C T I O NOviparous vertebrates typically have breeding seasons in which vitellogenesis (the synthesis of yolk and its appearance in the developing ova), ovulation and oviposition are confined to well-defined, usually brief periods of the year. During this time a characteristic sequence of ovarian events may be observed in the great majority of lower vertebrate species. Initially the ovary is small and the oocytes are devoid of yolk; during vitellogenesis the ova grow more or less synchronously so that at any one time they are all similar in size, and when fully grown they are ovulated and laid together over a short period. Normally one such cycle of a few weeks or months is completed in a year; this appears to be generally true, with certain exceptions, at all latitudes.Breeding in females of the elasmobranch Scyliorhinus canicula L. (lesser spotted dogfish) is cyclical but the period of the cycle is unusually long. Examination of the single ovary throughout much of the year reveals growing eggs in a distribution of sizes from minute previtellogenic oocytes to mature yolk-filled ova of 1-5 cm diameter. Within the upper size range the distribution is discontinuous and oocytes are found in pairs in a rapidly decreasing hierarchy of sizes. After ovulation of a mature pair, one ovum passes down each of the paired oviducts (Metten, 1941); during this passage it is provided with a horny shell. Estimates of the frequency of oviposition in the wild vary from one pair every six days (Harris, 1952) to 10-15 P au " s P e r annum (Le Danois, 1913). Superimposed on this pattern of egg production the following cyclical constraints have * Present address:

Maturity, reproductive cycle, and fecundity of spiny butterfly ray, Gymnura altavela (Elasmobranchii: Rajiformes: Gymnuridae), from the coast of Syria (eastern Mediterranean)

“…A larger liver may allow females to maximize the production of yolk such as in the viviparous. Moreover, cartilaginous fish store energy as lipids in the liver (Craik 1978). In viviparous females larger liver observed may be related to the increased energy expenditure during vitellogenesis, oocyte maturation, and gestation as well as females store large quantities of lipids in the liver during the reproductive cycle (Lucifora et al 2005).…”

Reproductive biology of deep-sea catsharks (Chondrichthyes: Scyliorhinidae) in the eastern North Pacific

“…Changes in liver mass were analyzed using the hepatosomatic index (I H ), I H = (HB -1 ) · 100, where H is the total liver mass and B is the total body mass of the specimen. Hepatic lipids are used in vitellogenesis, the formation of oocyte yolk (Craik 1978;Hamlett and Koob 1999), and it was expected that any seasonal variability in I H would coincide with inverse fluctuations in I G . Gonadosomatic and hepatosomatic indices were compared by month, with significant difference determined by plotting standard error (S.E.)…”

“…Previous studies suggested that gonadosomatic and hepatosomatic indices may fluctuate as a result of the production of gametes and the metabolic costs incurred through reproduction (Craik 1978;Sumpter and Dodd 1979;Parsons and Grier 1992;Maruska et al 1996;Richardson et al 2000). An increase in I G implies reproductive readiness, which may occur at first reproductive maturity or at peak times of reproductive activity (Parsons and Grier 1992;Maruska et al 1996).…”

“…Hepatosomatic index values were thought to vary because of the use of hepatic lipids in the formation of gametes or because of metabolic costs incurred during the processes of mate location and copulation (Craik 1978;Sumpter and Dodd 1979). There is an inverse I G -I H relationship in some scyliorhinids at the onset of reproductive maturity (Craik 1978;Richardson et al 2000).…”

The condition conundrum: application of multiple condition indices to the dusky shark Carcharhinus obscurus

“…*p < 0.001 the study region (Allen & Cliff 2000). Craik (1978) identified an increase in HSI (from ca. 5 to 8%) for female lesser spotted catsharks Scyliorhinus canicula in the Irish Sea.…”