Hormonally Induced Spawning, Embryonic Development and Larval Rearing of the Southern Temperate Banded Morwong Cheilodactylus spectabilis

Abstract

Banded morwong (Cheilodactylus spectabilis) are of interest for marine finfish aquaculture in temperate southern Australia. To improve their ovulatory response, adult females were implanted during the autumn spawning season with slow-release pellets containing 0-400 ug luteinizing hormone releasing hormone analogue (LHRHa)/kg body weight within 24 h of capture from the wild. Compared to the sham control group, animals treated with LHRHa produced significantly more eggs on each day after implantation for the following 7 days (91 +/- 39 ml and 290 +/- 38 ml) and a higher proportion ovulated (8/12 and 27/27). Of fish treated with LHRHa, 93% ovulated two days after implantation and 79% ovulated three times at two-day intervals, whereas control animals showed no cyclicity of ovulation and few ovulated more than once. Egg production was highest at the first ovulation after LHRHa treatment and declined at subsequent ovulations. In a second experiment investigating the range 100-400 ug LHRHa, there was no effect of dose rate on ovulation parameters which additionally examined implantation either immediately after capture or after a 5-day delay. Compared to immediate implantation, a delay resulted in a lower proportion of animals which could be stripped after implantation (100% and 50%, respectively) and the volume of eggs was lower (135 +/- 15 ml and 107 +/- 10 ml). The egg quality was poor following delayed implantation, resulting in no fertilisation after artificial insemination compared with immediate implantation in which fertilisation and hatch rates were higher for eggs collected on Day 2 after implantation (79 +/- 8% and 58 +/- 9%) than on Day 4 (23 +/- 7% and 15 +/- 6%). Thus, it is important to implant animals as soon as possible after capture to ensure optimum egg quality. Good quality eggs were buoyant, spherical and had a diameter of 1050 +/- 25 um with a single pigmented oil droplet of 190 +/- 9 um. When a separate large batch of eggs collected two days after implantation with 100 ug LHRHa was inseminated and cultured at 18 C, larvae hatched after 63 +/- 2 h at a standard length of 2.6 +/- 0.4 mm. Newly-hatched larvae were buoyant and transparent with only a few melanophores, eyes were non-pigmented and jaws were non-funtional. By the fourth day, jaws were functional and eyes were fully pigmented. Utilisation of the endogenous yolk and oil was completed by Day 6 and swimming commenced with exogenous feeding. Larvae, initially fed lipid-enriched rotifers followed by Artemia, reached 8.9 +/- 0.7 mm length on Day 55, after which they metamorphosed to the post-larval paperfish stage of development, 22 +/- 0.9 mm on Day 100, and 43 +/- 1.0 mm at six months old. The results show that treatment of wild-caught females with slow-release pellets containing LHRHa is effective for the production of eggs for hatchery rearing.