Baskerville-Bridges, B., Kling, L.J.
Abstract:
Successful culture of many marine finfish species has been difficult due to high mortality experienced during the early life stages. Live feed organisms (ie/rotifers and Artemia) have consistently resulted in superior growth and survival in larval feeding trials when compared to microparticulate diets (MPD). The purpose of this study was to introduce a commercially available MPD to Atlantic cod (Gadus morhua) larvae at four different weaning times to determine how early it could effectively replace live feed organisms.
Fertilized cod eggs were received from the National Marine Fisheries Service at the Narragansett lab in Rhode Island. They were disinfected upon arrival and incubated between 6-8(C. Continuos aeration was applied to provide motion of the eggs within the experimental tanks. Each tank was stocked with approximately 1200 larvae (55 larvae/liter). At first feeding (1 day post-hatch), the temperature was increased 1(C/day until 10-11(C was achieved. The lighting was increased from .6lum/ft^2 at this time and further increased to 3.0 lum/ft^2 on day 29. The cod larvae were kept on a 24 hr light/0 dark photoperiod throughout the study.
The microparticulate diet 5BioKyowa) was given to the cod larvae at four different weaning times. In treatment 1, rotifers, Artemia, and the MPD were introduced on 1, 26, and 29 days post-hatch respectively. The diets were co-fed for 7 days. In treatment 2, rotifers were added at day 1 and the MPD at day 29. In treatment 3, rotifers were added at day 1 followed by the MPD on day 22. In treatment 4, larvae received rotifers at day 1 and the MPD was introduced on day 15. In treatment 5, rotifers were fed on day 1 and the microparticulate diet was given at day 8.
Twenty larvae from each of the 20 tanks (n=4) tanks were sampled on 1, 8, 15, 22, 29, 36, 43, 50, 57, 64, and 71 days post-hatch. Images of the larvae were saved for length measurements (Image ProPlus). Larvae were then frozen for dry weight and fatty acid analysis. Histological samples were also taken from each treatment after introduction of the MPD to determine digestibility of the diet. At the end of the experiment larvae in each tank were counted and survival was calculated.
In treatments 1, 2, 3, and 4 the cod larvae accepted the MPD shortly after introduction. The majority of larvae in treatment 5 however did not begin feeding on the MPD until day 14. Percent survival up to 71 days was 34.8+/-7.0, 32.7+/-2.0, 39.4+/-1.8, 35.0+/-3.9, and 33.8+/-4.9 for treatment 1, 2, 3, 4, and 5 respectively. Length of cod larvae was comparable among treatments 2, 3, 4, and 5. Larvae in treatment 1, however, were larger than the other experimental groups.
Weaning can begin as early as 15 days posthatch, however, prior to this time, little MPD was consumed. Survival was equivalent in all treatments. Introduction of a MPD at an earlier time reduces the need for live feeds. Growth through metamorphosis can be successfully achieved without Artemia. However, larvae from treatment 1, resulted in the better growth than the other experimental groups.
(Dept. of Animal, Veterinary and Aquatic Sciences, University of Maine, 5763 Roger Hall, Orono, ME 04469-5763)
***************