The reproductive biology and induced spawning of striped trumpeter, Latris lineata

Sampling of Latris lineata (n= 334) was conducted with commercial fishers on the east coast of Tasmania between May 1990 and May 1992. Relationships between fork length and weight, and age and fork length are presented for Latris lineata. Macroscopic descriptions of the stages of gonad maturation for male and female Latrislineata are verified from histological studies. A gonad index (GI = gonad weight (g)/fork length (cm) x 105) is used to show that the spawning season of Latris lineata extends from September to October. A critical GI value of approximately 25 is proposed to distinguish female Latris lineata in advanced stages oocyte development prior to spawning. Analysis of frequency distributions of the diameters of developing oocytes shows that three distinct batches of developing oocytes can be distinguished in the ovaries of Latris lineata approaching spawning. This information indicates that female Latris lineata spawns multiple batches of eggs, which develop in a group synchronous manner. Female Lairislineata mature earlier (5 years; FL = 43.8 cm) than males (8 years; FL = 53.4 cm). A study in 1990 suggested that intra-peritoneal injection of 0.5 ml/kg b.w. of Ovaprim¬¨vÜ (Salmonid gonadotropin releasing hormone (sGnRH)with domperidone) could induce ovulation in Lairis lineata. An investigation in 1991 compared interperitoneal (i.p) injection of Ovaprim R with i.p. injection of lutenizing hormone releasing hormone analogue (LHRHa) at dosages of IORg/kg b.w., 2514/kg b.w., and 50ii.g/kg b.w. No significant difference (P> 0.05) between treatments was shown. Females with initial oocyte diameters of 600 pm or greater were induced to complete final oocyte maturation. Two experiments conducted in 1992 investigated the effect of monthly (July-September) intramuscular implantation of cholesterol (90%) and copha (10%) pellets containing LHRHa and 17a-methyltestosterone (17a-MT) on circulating levels of 17t3-estradiol and testosterone. One experiment found no significant effect (P> 0.05) of a high and low dose LHRHa+17a-MT implant regime, on mean oocyte diameter. Only one hormone implanted fish ovulated a batch of eggs in this investigation. No significant effect (P> 0.05) on mean serum 170-estradiol and testosterone due to implant treatment dosage was shown. Mean serum levels of 17f1-estradiol showed no significant (P> 0.05) change at 24 hr following implanting, for any treatment, at any month. For high dose hormone treatment fish, mean serum testosterone had decreased significantly (P< 0.05) at 24 hr following the July implant, while mean testostoterone of control fish showed a significant increase (P< 0.05) at this time. In the second experiment, 2 of 7 mature female Latris lineam implanted with the high dose LHRHa+17a-MT pellet formulation were induced to ovulate. One fish ovulated 11 times and the other ovulated 9 times, mostly at 3 day intervals. The first of these fish ovulated a batch of eggs 21 days before the first ovulation by a control fish. Both control fish released one egg batch spontaneously. No significantly (P> 0.05) change in either mean oocyte diameter or mean serum levels of 17f3-estradiol or testosterone were found between hormone implanted and control fish, at any month. Mean serum 1713-estradiol was significantly (P< 0.05) higher in the 2 implanted fish, than control fish, at the time of the first (July) and second (August) implants. A significant (P< 0.05) decrease in mean serum testosterone of hormone treated fish was recorded at 144 hr after implanting in July, while a significant (P< 0.05) increase in this steroid was recorded at 144 hr following the August implant.