15 JULY 1999
FORAGING, GROWTH AND SURVIVAL OF ATLANTIC COD LARVAE REARED IN DIFFERENT PREY CONCENTRATIONS
V. Puvanendran, J.A. Brown-1999
Aquaculture: 175(1-2) : 77-92 (from Current Contents)
Abstract:
Laboratory studies have shown that suboptimal prey concentrations during the first feeding usually result in slower growth and higher mortality. We investigated the growth, survival and foraging behaviour of Atlantic cod (Gadus morhua) larvae in different prey concentrations under laboratory conditions. Larvae were reared from hatching to metamorphosis (6 weeks post-hatch) on rotifers and/or Artemia nauplii at 250, 500, 1000, 2000, 4000, 8000 and 16,000 prey 1(-1) Once a week, standard length and myotome height were recorded and mortalities were monitored from day 15. Observations on feeding behaviour were recorded twice a week. Larvae reared at 4000-16,000 prey 1(-1) were significantly larger and had significantly higher condition indices than larvae from lower prey concentration (less than or equal to 2000). Initially, specific growth rates (SGR) were significantly higher in larvae reared at higher prey concentrations (greater than or equal to 4000), but from 3 weeks post-hatch, no difference was found among treatments in SGR. Instantaneous mortality rates (Z) decreased in all treatments as the larvae grew. Survival was significantly lower for larvae reared at lower prey concentrations until week 3. Larvae reared at 250 and 500 prey 1(-1) did not survive beyond days 11 and 24, respectively. Survival of larvae was significantly higher at higher prey concentrations at weeks 2 and 6 post-hatch. Although survival of cod larvae at week 2 was similar among the three highest prey concentrations; survival at the end of the experiment (week 6) was higher, but not significantly, in the 4000 prey/1 treatment than the other two treatments (8000 and 16,000 prey/1). Swimming duration was significantly higher among larvae reared at lower prey concentrations. Larvae reared at higher prey concentrations (2 4000) showed higher orientation and captured success rates but lower attack rates than larvae reared at lower prey concentrations. Our results indicate that for intensive rearing of cod larvae, higher prey concentrations are required to sustain reasonable growth and survival than that have been reported for mesocosm studies.
(Huntsman Marine Sci Ctr, Brandy Cove Rd, St Andrews, NB E0G 2X0, Canada, e-mail: vpuvanen@morgan.ucs.mun.ca)