Aspects of the reproductive biology of Puntius schwanenfeldi (Blecker), a Malaysian cyrinid

A broad scope investigation examined the reproductive biology of Puntius schwanenfeldi in order to provide information relevant to the induction of spawning. Experiments investigated a number of facets of the hormonal induction of spawning, but were unable to define reliable procedures for inducing spawning behaviour, oviposition, or in vitro fertilization. Rearing conditions were suggested as a probable reason for the lack of success. The annual reproductive cycle of Puntius schwanenfeldi in the Perak River, Malaysia, was investigated to establish baseline information about its reproductive ecology and proximate environmental cues potentially regulating the timing of reproduction. During the 19 months studied six spawning periods were identified based upon the observation of a mature sized fish (>160 g) whose ovaries had a volume fraction of stage IV oocytes (IV-V%) less than 0.46. Spawning periods were also identifiable, but less accuracy, based upon the presence of post ovulatory follicles within the ovary. A GSI threshold of 2 also provided accurate identhication of spawning periods. Throughout the year all females greater than 160 g were mature or rematuring. Females may spawn more than once whin years. Spawning periods were primarily associated with increased water level in the Pelus River, an unregulated tributary of the Perak River. Regulation of the mainstem of the Perak River by hydroelectric dams dampens changes in physical hydrology, and may have influenced the reproductive seasonaIy of this species. Male condion was assessed by monoring GSI and the abundance of tuberculated males. Patterns in the reproductive seasonaly of males did not coincide closely wh female patterns. Investigation of ovarian rematuration was undertaken in order to describe ovary condition at various stages of rematuration and to assess the rematuration rate. Females were induced to ovulate and then sampled at 1, 5, 15, and 30 days. P. schwanenfeldi has group synchronous ovarian development and rematuration occurs in two phases. In the first phase IV-V% increased due to vitellogenesis, but there was only a limited increase in GSI. In the second phase continued vellogenesis led to increased GSI as a result of an increased number of vitellogenic oocytes. Post ovulatory follicles were visible for up to five days. The IV-V% was statistically lower than in mature day 30 fish for up to 14.5 days. After 30 days of rematuration fish are probably able to ovulate again. Increased plasma gonadotropin one day post-ovulation was associated with the initiation of vitellogenesis. Plasma estradiol was elevated in some individuals only during the most active phase of vitellogenesis. Plasma testosterone levels showed no differences over the course of rematuration. A final experiment examined methods for the induction of tuberculation using exogenous testosterone (T), 11 -ketotestosterone (11-1(T), and 1 7o methyltestosterone (MT). MT 1 pg/g, MT 10 igIg, T 1 jig/g, T 10 tg/g, 1 1-KT 1 jiglg and saline were administered every second day by injection. MT at 1 tg/g and 10 pgIg and T at 10 tg/g readily induced tuberculation. Tubercles developed on the dorsal surface between the head and dorsal fin, the opercula, the belly, the first dorsal ray, and along the sides of the fish. 1 1-KT did not yield an effect significantly different from control fish. Plasma levels of T and 11 -KT were examined but only the T 10 tgfg group showed elevated T levels as a result of treatment. The effect of holding experimental fish in groups is discussed in relation to these results.Science, Faculty ofZoology, Department ofGraduat