Reproduction and growth in the lesser-spotted dogfish Scyliorhinus canicula (Elasmobranchii; Scyliorhinidae), from the west coast of Ireland

The reproductive biology and von Bertalanffy growth parameters were investigated in lesser-spotted dogfish from the west coast of Ireland. The length at 50% maturity was similar for both sexes, occurring at 57.5 em in males and at 58.1 cm in females. Age at maturity was estimated as six years. The number of oocytes displayed a marked seasonal cycle, which was lowest in March, and highest in November. Observations on maximum oocyte diameter indicate that ovulation occurs at 1.7 - 1.8 cm, and oocytes of this diameter were recorded throughout the study. Additionally, females with egg-cases in utero were also observed throughout the year, indicating a protracted breeding season, although peak egg-laying occurred in May, and was minimal in October. Gonad indices indicated that the male and female gonadal cycles were not synchronous, supporting the idea that females store spermatozoa. Based on this and previous studies, it appears that there are geographical variations in certain aspects of the reproductive biology. Vertebral bands were enhanced using an acid decalcification technique, and for the purpose of the study, bands were assumed to be annual in nature. The von Bertalanffy equation was estimated as l(t) = 82.7(1-e(-0.15(t + 1.36))), and was similar to a length-frequency generated equation calculated for dogfish in Spanish waters.