Reproductive biology and growth during pre- and postnatal life of Trygonoptera personata and T. mucosa (Batoidea: Urolophidae)

This study demonstrates that the females and males of two species of ray (Trygonoptera personata and T. mucosa) attain between ∼33 and ∼49% of their asymptotic sizes by the time of parturition, and that their growth throughout the whole period of pre- and postnatal growth can be described well by a single and smooth growth curve. The individuals used for this study were caught at regular intervals by trawling along the lower west coast of Australia. Conception takes place at a similar time in both Trygonoptera species (i.e. between late autumn and mid-winter), and parturition occurs 10-12 months later. The eggs found in the left uterus of female T. personata were enclosed in a membranous egg case and remained in embryonic diapause for ∼5 months between mid-winter and late spring, which is the first recorded instance of such diapause in a urolophid. Embryonic diapause in T. personata was followed by a period of particularly rapid embryonic development, during which the mean disc width increased from 11 mm in December to 113 mm in April, when parturition occurred. Although no females of T. mucosa were caught with either eggs or embryos in certain months, the data still showed that their eggs are enclosed in a case and that their embryos grow less rapidly than those of T. personata. Trygonoptera mucosa attained greater maximum disc widths than T. personata both in females (369 vs 311 mm) and males (283 vs 269 mm). The maximum ages attained, after parturition, by the females of T. personata (16 years) and T. mucosa (17 years) were greater than those of their males (10 and 12 years, respectively). Maturity is typically attained by the females of T. personata and T. mucosa at ∼230 and 250 mm, respectively, and by the males of both species at ∼220 mm. Maturity was reached by at least 50% of the females of T. personata and T. mucosa by the end of their fourth and fifth years of life after parturition, respectively, and by > 50% of the males of these two species by the completion of their fourth and second years of life after parturition, respectively. The von Bertalanffy and Schnute growth equations for the females and males of both species provided a good fit for the disc widths-at-age of postnatal fish, with r2 values for these equations ranging from 0.874 to 0.938. Although the von Bertalanffy growth curve also provided a good fit for the disc widths-at-age of both sexes of both species throughout much of the total growth period (i.e. including embryonic growth), it did not accommodate well the disc widths-at-age of the oldest and largest fish. This latter deficiency was entirely or largely eliminated by the use of the Schnute growth equation (r2 values ranged from 0.919 to 0.938), which incorporates four rather than three parameters as in the von Bertalanffy growth equation