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

Experiments were conducted to investigate larval mortality in cultured summ er flounder during the first 2 weeks after hatch. The influence of feeding success, parentage, addition of algae, water quality, and the microbial com munity on mortality during this period were investigated. Larvae were raise d in 2-1 bowls at initial densities of 50 or 75/I with mild aeration, 12 L: 12 D photoperiod, and regular 50% water changes. In all experiments, mortal ities were recorded and removed daily. In the first two experiments, daily samples of larvae were taken to assess feeding success and to relate that t o survival. The second experiment investigated the effects of both feeding success and the addition of algae to larval culture bowls on larval surviva l. The third experiment investigated the effects of water quality and bacte rial load on survival during the experimental period. The first two experim ents indicated that failure to establish feeding is probably not the cause of catastrophic mortality of the larvae, although a statistical relationshi p 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 expe riments (both within and between parental crosses) suggesting that catastro phic mortalities were due to rearing conditions in addition to gamete quali ty. The addition of algae to larval cultures increased survival from 13 +/- 24% (n = 33) in the absence of algae during the first experiment to 46 +/- 39% (n = 49) with the addition of algae during the second experiment. The final experiment indicated that larval mortality was not linked to the meas ured microbial or water quality conditions. The relationship between the pe rcentage of floating eggs at time of fertilization and survival at 10 days after hatch was not significant. (C) 1999 Elsevier Science B.V. All rights reserved.