From July 1996 to December 1997 the reproductive cycle of male and female Holothuria scabra was monitored for a local population at Stradbroke Island, Moreton Bay (27°30' North, 1 53°24' East) Australia. The gutted weight gonad index peaked in November of both years while no obvious progression of oocyte size was noticed. Gametogenesis coincided with a period of body wall weight loss from mid-winter (June) to mid-summer (December). During gametogenesis mature oocytes were observed and were either reabsorbed or spawned, during or prior to, the vitellogenic period from September to November. It was likely that stored nutrients in the body wall were used for gametogenesis during the latter part of winter and that in response to its environment, the production of ripe ova was regulated by phagolytic activity.
Animals collected from October 1996 to January 1997 were maintained in captivity at the natural temperature and light cycle existing at that time and subsisted on the detrital material contained in the sand in the holding tank, losing up to 40% of their wet weight over 2 months. The weight of animals continued to decline for a period of 3 months post-spawning, despite the addition of prawn and lucerne pellets to promote bacterial and fungal growth in the substrate. Animals collected during October 1997 were conditioned at 27°C and a 16:8 LD (light/dark) photoperiod. Diets provided to broodstock reduced the amount of weight loss, reaching approximately 10% after 1 month, compared with 20% for the controls. Animals were more active at night, produced more faeces in the control and blue crab diet quadrats and spent a large proportion of time moving along the perimeter of quadrats, while movement across the substrate depended on the distribution of food. The degree of weight loss in captivity may depend on the interaction of diet, temperature and light and the effect these variables have on the coupling of feeding behaviour with the reproductive strategy of H. scabra.
During the 1997/98 summer, between 1 and 5 weeks of captivity, 100% of animals were induced to spawn in four trials at dusk on or close to a new or full moon, using 9 males and 9 females contained in a 1.5 m2 area and 20 to 30cm of 1 µm filtered sea water, using a 3 to 5°C temperature shock. H. scabra was induced to spawn in small numbers during the 1996/97 summer despite a marked degree of weight loss and all induced individuals spawned during the 1997/98 summer, irrespective of diet in captivity. No correlation was found between egg size and hatch rate, fecundity, fertilisation rate, weight or number of days in captivity, for females. The difference in fecundity between animals of similar size and mean fecundity in consecutive trials, decreased the longer animals were held in captivity before spawning. The hatch rate of eggs was reduced significantly for broodstock held for 1 month and was most likely affected by: i. the expiration of gonad nutrients for egg metabolism when held for extended periods before spawning and the resulting use of yolk reserves to maintain egg viability once vitellogenesis was completed; ii. the use of gonad and egg nutrients for somatic metabolism when other nutrient sources ran out. Hatch rate and fecundity are important indicators of egg viability of broodstock maintained in captivity for an extended period.
It was found that in excess (40 and 80 x 103 cells/mL), and in the absence of the alga Isocrysis galbana, larval survival was less and growth and development was inhibited. In moderate amounts of algae (10 and 20 x 103 cells/mL) the percentage of growth, survival and development of larvae increased substantially. The instantaneous mortality rate (larvae/day) of larvae varied throughout development in all feeding regimes and between bowls within a treatment, but was least overall in moderate amounts of algae.