Nursery culture of Haliotis
rubra: the effect of cultured algae and larval density on settlement and
juvenile production
S. Daume, S. Huchette, S. Ryan, R.W. Day-2004
Aquaculture, 236(1-4): 201-209
Abstract:
In the present study we investigated the use of a
green macroalga Ulvella lens on a commercial scale to improve the
settlement and early growth of Haliotis rubra larvae. Two
conditioning methods were evaluated comparing plates covered with U. lens
grown over 4 and 18 days. An average settlement rate of 62% was estimated 3
days after larval release. This rate is amongst the highest recorded in
commercial nurseries, suggesting that this technique of conditioning the
settlement plates was efficient and reliable. Larvae showed a clear
preference for older plates with a lower cover of U. lens. Larvae
were released at two densities (50,000 and 100,000 larvae per 1000 l tank
representing approximately 0.25 and 0.5 larvae cm−2 of
substrate, respectively) to investigate if larval density influences overall
settlement rate and later performance. Larval release density did not have a
significant effect on settlement rate.
After settlement, plates were randomised and the food
density was enhanced. Half of the tanks were inoculated with the cultured
diatom Navicula sp. and the other half received a mix of naturally
developing diatom species, to determine the effect on growth and survival
over a period of 4 months. We demonstrated that the type of substrate on
which the larvae settled, light (which affects the food density but may also
affect the oxygen level in the boundary layer of the biofilm) and the
density of post-larvae have very marked effects on growth. Survival was
strongly density-dependent after 64 days and the instant mortality rate (M)
decreased from 43.7 in the first 10 days to 5.4 between 22 and 64 days after
settlement.
These results provide crucial technical and
ecological information on the early development of H. rubra in the
nursery and suggest that the use of U. lens will provide substantial
improvements in nursery performance.
(School of Ecology and Environment, Deakin
University, P.O. Box 423, Warrnambool, Victoria 3280, Australia, e-mail: sdaume@fish.wa.gov.au)