Larval performance, osteological development and skeletal abnormalities in wreckfish (Polyprion americanus) under a standard rearing protocol and different light intensities and rearing temperatures

Wreckfish (Polyprion americanus) is a promising new species for aquaculture diversification due to its fast growth, late reproductive maturation, and high market price. Nowadays, low larval survival is considered the biggest limitation in wreckfish farming. Here, the fertilization, hatching and survival rates of 20 spawning events from an established wreckfish broodstock have been analyzed in order to characterize the main bottlenecks in wreckfish early and larval development. The ontogenesis of the skeletal system and the incidence of skeletal deformities have been assessed in 632 samples from larval rearing trials using currently available protocols. Furthermore, the effect of different rearing temperatures (13 vs 16 °C) and light intensities at water surface (600, 900 and 1200 lx) on the skeletal development have been also explored. Results showed as while a variable egg fertilization rate (61.75 ± 34.62%) were achieved, a very poor hatching (4.52 ± 9.27%) and survival rate (0.01 ± 0.00%) until 71 days post hatching (dph) were observed. Swim bladder inflation was first seen at 7 dph, and at 11 and 25 dph a 61–63% of fish functional swim bladder. The first skeletal structures to be formed were those related with breathing and feeding activities (e.g., cleithrum, Meckel's cartilage and ceratobranchials) and were visible in larvae of 4–5 mm of standard length (SL). Ossification of the vertebral column progressed in an anterior-to-posterior direction, being fully ossified at 7–14 mm of SL. Regarding the skeletal deformities, a high incidence (63%) of jaw deformity (particularly lower jaw deformity) was observed in larvae of 4–5 mm of SL, progressively decreasing (up to 5%) in larvae of >6 mm of SL. Deformed vertebrae (compressed, fused, and/or displaced) were mainly located at 13 to 15th vertebra, and were associated to lordosis, most probably due to the no swim bladder inflation. No clear relationship between temperature and the incidence of lower jaw deformity was observed during endotrophic larval development. Light intensity had a clear effect on survival but not in skeletal development. Larvae reared under 600 lx had lower survival (0.15 ± 0.21%) at 21 dph than when reared with 900 and 1200 lx (0.6 ± 0.28 and 0.7 ± 0.28%, respectively). The present research work represents an important step forward to solve wreckfish larval rearing bottlenecks, suggesting that while temperature and light intensity might have an effect on wreckfish larval survival and development, egg quality and incubation seemed to be the most limiting factors for successful wreckfish aquaculture.