The effects of salinity of holding water of 5 parts per thousand, 20 parts per thousand or 35 parts per thousand on seasonal reproductive development, plasma steroid levels, the efficacy of luteinizing hormone releasing hormone ethylamide (LHRHa) to stimulate ovulation, sperm motility, and egg fertility and development to hatching were investigated. Fish were captured from the wild from December to February, placed into salinity regimes in May and held until the normal times of spawning the following November. Blood samples were taken in August, September and November. Female fish were injected with saline or LHRHa (50 mu g kg(-1)) in November and bled and checked for ovulation for 5 days. Gonadal maturation was unaffected by salinity in both sexes. In females, seasonal plasma steroid levels were unaffected by salinity, whereas in males, plasma levels of 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) and 11-ketotestosterone were higher in fish held at 35 parts per thousand than in fish held at 5 parts per thousand in September, and in fish held at 5 parts per thousand and 20 parts per thousand in November, respectively. Plasma estradiol (E-2) and testosterone (T) levels in saline-injected fish, either remained low or were significantly suppressed. LHRHa treatment resulted in the short-term elevation of plasma E-2 and T levels at all salinities, whereas plasma 17,20 beta P levels were elevated over controls on days 1 and 2 post-injection in fish held in 20 parts per thousand, but remained unchanged in fish held in 35 parts per thousand or 5 parts per thousand. All but one fish ovulated in response to LHRHa, however, the number of ovulations and egg volumes was lowest in fish held at 5 parts per thousand. Both fertilisation and sperm motility were significantly reduced at 5 parts per thousand. Naturally fertilised eggs (35 parts per thousand; 2-8 cell stage) were incubated to hatching at salinities of 0 parts per thousand, 5 parts per thousand, 10 parts per thousand, 15 parts per thousand, 20 parts per thousand, 25 parts per thousand, 30 parts per thousand or 35 parts per thousand. Eggs hatched in all salinities except 0 parts per thousand, but with lowered survival at 5 parts per thousand and 10 parts per thousand. Larvae showed high levels of deformity at salinities below 15 parts per thousand. (C) 2000 Elsevier Science B.V. All rights reserved.
