Skeletal ontogeny and deformity during the early fry culture process for Epinephelus lanceolatus

Skeletal development is crucial for fish fry breeding because of its influence on fish external morphology, functional exercise, and even survival rate, especially in groupers due to their extremely high incidence of deformity and mortality. Groupers are important mariculture fish species with high commercial value, however, research on fry early development in groupers is limited, especially for Epinephelus lanceolatus (Bloch, 1790). In the present study, we cultivated E. lanceolatus larvae and juveniles and systematically investigated the timing and progression of skeletal development, and the types and incidence of skeletal deformities during the fry culture process. Our results revealed that the skeleton associated with jaw elements, gill components, and the dorsal and pelvic spine appeared and ossified preferentially. The timing and progression of skeletal development was significantly correlated with the functional requirement for food ingestion, respiration, and swimming capacity.Notably, a 96% incidence of deformities was observed before 20 days post hatching (dph), including cranium deformities (82%), spinal deformities (13%), and fin deformities (1%). Cranium and spinal deformities significantly affected the external morphology and growth, which might be a major reason for the low survival rate during early development stages. After 20 dph, the incidence of deformities decreased greatly, although significant cannibalism was observed in 20%–30% of large individuals during the first fry separation at 45 dph, and this would be another factor leading to a lower survival rate. The survival rate of 40 dph juvenile E. lanceolatus was only approximately 1.2%. The results of the present study provide useful information for understanding skeletal development and optimizing fry breeding technologies in groupers.