Early morphological and physiological parameters of survival and mortality in cultured southern flounder (Paralichthys lethostigma) larvae

This study focused on the relation between larval southern flounder (Paralichthys lethostigma) growth, cardiac performance, and metabolic physiology (metabolic rate, hormones). Two-way ANOVAs were performed among larvae groups that successfully survived through metamorphosis (n = 1) vs. those that succumbed to mass mortality early in development (n = 2). Larvae were monitored from 5 to 50 days post hatch (dph). The comparison of morphological and physiological parameters for the three batches for equivalent life-stages from 5 to 12 dph (n = 8-10/dph), showed specific growth rate (SGR) in the surviving larvae to be ~3-fold higher than the two failed batches. Similarly, the absolute oxygen consumption rate (AMO₂) was ~5-fold higher in the surviving batch vs. the two failed batches. In contrast, mass specific oxygen consumption rate (MO₂) and heart rate (HR) were significantly lower in the surviving batch (~3-fold) versus the two failed batches. This mismatch for the surviving batch (a high SGR contrasted with low MO₂ and HR), suggested a reduced cost of growth and likely bioenergetic conservation prior to metamorphosis-an energetically demanding process. The subsequent monitoring of the surviving batch through metamorphosis (~30-40 dph), showed a ~ 10-fold increase in AMO₂ and ~ 2-fold increase in thyroid and corticoid hormones. Lastly, a strong negative correlation of HR vs. MO₂ during early development putatively suggested future batch failure.