Effect of treatment with LHRH analogue on oocyte maturation, plasma sex steroid levels and egg production in female striped trumpeter Latris lineata (Latrididae)

Abstract

Striped trumpeter Latris lineata (Schneider, 1801) are currently being investigated for their aquaculture potential. Little is known of the reproductive physiology of this fish and a limited supply of eggs is hindering larval rearing trials. This study assessed the effect of hormone therapy to induce ovulation in wild caught broodstock. Female striped trumpeter were implanted with 0, 100 or 200 μg kg −1 body weight of a synthetic luteinizing hormone releasing hormone analogue (LHRHa: des-Gly 10, [ d-Ala 6]-LH-RH ethylamide), administered in a slow release cholesterol pellet ( n=12 per treatment). Blood and ovarian samples were collected daily from each fish, and the volume of eggs produced was recorded. Plasma levels of testosterone (T), 17β-oestradiol (E 2) and 17α20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured by radioimmunoassay. Four, 11 and 12 fish treated with 0, 100 or 200 μg kg −1 LHRHa respectively, ovulated. When compared to the control group, both LHRHa treatments resulted in significantly increased ( P<0.05) egg volumes overall and also on Day 4 post-implant in terms of daily volumes. Whilst there was no significant difference ( P>0.05) in egg volumes between the two LHRHa treatments, when combined, two groups could be defined; those fish that underwent only `one or two ovulations' (OTO) and those that underwent `three or more ovulations' (TMO). The OTO fish ( n=11) had similar plasma steroid levels to the control fish whereas the TMO fish ( n=12) had significantly increased ( P<0.05) plasma levels of T, E 2 and 17,20βP, with peaks occurring on Day 1 for T (4.8 ng ml −1) and on Day 2 for E 2 and 17,20βP (2.2 and 1.3 ng ml −1, respectively). Twenty-one of the 24 LHRHa-treated fish first ovulated on Day 4 and, in the TMO fish, subsequent clutches of eggs were produced approximately every 3 days for up to 5 cycles. Oocyte recruitment appeared to originate from pre-vitellogenic oocytes from the third clutch onward. This work identified female striped trumpeter as multiple spawners with group synchronous oocyte development and showed LHRHa to be an effective stimulant for the induction and synchronization of ovulation.