Investigations into the causes of early larval mortality in cultured summer flounder (Paralichthys dentatus L.)

Abstract

Experiments were conducted to investigate larval mortality in cultured summer flounder during the first two weeks after hatch.The importance of feeding success,parentage, addition of algae, water quality, and the microbial community to mortality during this period were investigated. Larvae were raised in 2-L bowls at initial densities of 50 and 75/L with light aeration, 12L:12D photoperiod, and regular 1-L water changes.In all experiments mortalities were recorded and removed daily. In the first two experiments daily samples of larvae were taken to assess feeding success and to relate that to survival.The second experiment investigated the effects of both feeding success and the addition of algae to larval culture bowls on larval survival. The third experiment investigated the effects of water quality and bacterial load on survival during the experimental period. The first two experiments indicated that failure to establish .feeding is probably not the cause of catastrophic mortality of the larvae, although a statistical relationship existed between feeding incidence and survival in two of six cases. High variability (34 ± 38% n=82) in survival was seen in the first two experiments (both within and between parental crosses) suggesting that catastrophic mortalities were due to rearing conditions rather than gamete quality. The addition of algae to larval cultures increased survival from 13 ± 24% (n=33) during the ii ·f i rst experiment to 46 ± 39% (n=49 ) during the second experiment. The final experiment indicated that larval mortality was not linked to the measured microbial or water quality conditions. The relationship between the percentage of floating eggs at time of fertilization and survival at 10 DAH was found to be not significant, providing further evidence that gamete quality was not as important as rearing conditions in these experiments.iii ACKNOWLEDGMENTS

Effect of cultivated copepods (Acartia tonsa) in first-feeding of Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae

“…The microbial environment in the rearing tanks has an effect on the early mortality and growth of marine fish larvae (Alves et al . ; Skjermo & Vadstein ). Other physical factors, such as the amount of aeration or water flow, could also have contributed to an unfavourable rearing condition.…”

“…Other factors beside the diet may have contributed to the high early mortality, which emphasizes the importance of a proper rearing environment during the early stages of development. The microbial environment in the rearing tanks has an effect on the early mortality and growth of marine fish larvae (Alves et al 1999;Skjermo & Vadstein 1999). Other physical factors, such as the amount of aera- . tion or water flow, could also have contributed to an unfavourable rearing condition.…”

Skeletal muscle growth dynamics and the influence of first-feeding diet in Atlantic cod larvae (Gadus morhuaL.)

“…Each treatment had three replicate tanks. To ensure equal prey density and prey size for all larvae, copepod nauplii ( Acartia tonsa ) (stage NIII-V, 170-210 µm) and rotifers ( Branchionus ibericus ) (180 µm in adult lorica length) of equivalent sizes (Alves et al, 1999; Penglase et al, 2010) were used for rearing the cod larvae from 3 to 28 dph, and the cod larvae were fed three times per day at a prey density of 12,000 litre −1 . In the copepod treatment, cod larvae (copepod-fed larvae) were fed with A. tonsa nauplii, cultivated on the micro algae Rhodomonas baltica .…”

Survival of larval summer flounder Paralichthys dentatus on formulated diets and failure of thyroid hormone treatment to improve performance

“…For all experiments, summer flounder larvae were obtained from broodstock fish maintained at the University of Rhode Island, Kingston, USA. Spawning and larval rearing were done according to the methods described by Bisbal & Bengtson (1993) and Alves et al . (1999 ).…”

“…For all experiments, summer¯ounder larvae were obtained from broodstock ®sh maintained at the University of Rhode Island, Kingston, USA. Spawning and larval rearing were done according to the methods described by Bisbal & Bengtson (1993) and Alves et al (1999). Brie¯y, larvae were reared in 150-L aquaria and fed rotifers Brachionus plicatilis that had been cultured on a mixture of two microalga species, Tetraselmis suecica and Isochrysis galbana, from ®rst-feeding at 3 days after hatch (DAH) until 15 DAH.…”