Effect of consecutive 9- or 12-month photothermal cycles and handling on sex steroid levels, oocyte development, and reproductive performance in female striped trumpeter Latris lineata (Latrididae)

Abstract

Duplicate groups of sexually mature striped trumpeter Latris lineata were maintained for two seasons on either a 12-month cycle of ambient temperature (9-18 degrees C) and photoperiod, or a 9-month compressed temperature and photoperiod cycle. One of the duplicates from each cycle was handled frequently (handled) and blood and ovarian samples taken monthly from females until the start of gonadal recrudescence, and then fortnightly until ovulations had ceased. Fish from the other group were not handled (non-handled), except near the end of their spawning seasons to determine which fish had ovulated. Naturally spawned eggs were collected daily from the tanks and hand-stripping was conducted fortnightly in the handled fish during the respective spawning seasons. The 12-month group started spawning in September in both years, whereas the compressed cycle advanced spawning by 1 and 4 months during consecutive seasons, i.e. August 1995 and May 1996. For all handled fish, oocytes developed to late cortical alveoli/early vitellogenic stage, but on average, only 64% of fish continued development through to ovulation. The duration of spawning averaged 45 days for the 9-month and 64 days for the 12-month cycle. The mean volume of eggs produced for each day of production was higher for the handled than the non-handled fish, but there was no difference between cycles (9- and 12-month). Eggs from fish on the 9-month cycle were significantly smaller than from fish on the 12-month cycle. Plasma levels of testosterone (T) and 17beta-oestradiol (E2) in fish from both the 9- and 12-month cycles were at or near their lowest levels at first sampling (<0.3 and 0.5 ng ml -1, respectively) and remained low except for elevations during the 3-4 month period of oocyte maturation and ovulation, when levels peaked at 1.3 and 6.3 ng ml -1, respectively.