Effect of salinity on egg hatching, yolk sac absorption and larval rearing of Senegalese sole (Solea senegalensis Kaup 1858)

Abstract

Assays carried out under laboratory-controlled conditions revealed that eggs of Senegalese sole, Solea senegalensis Kaup 1858, incubated at 10, 18, 27 and 33 grams per litre (g L⁻¹) reached their maximum hatching rates (above 80%) 48 h after incubation. In contrast, hatching was significantly delayed (24 h) and completely failed when the salinity was set at 5 and 0 g L⁻¹, respectively. Newly hatched and early-developing yolk sac larvae presented similar survival rates 3 days after hatching (DAH) when exposed to salinities of 10, 18, 27 and 33 g L⁻¹. Larvae incubated at 5 g L⁻¹ salinity died a few hours after hatching once they were released from their respective chorions. The notochord length was unmodified by salinity 5 DAH. Nevertheless, an overall lower myotomal height and a putative delay in the depletion of yolk sac were found in larvae reared at 10 g L⁻¹. This anomaly in overall larval development became more pronounced with the occurrence (100% of analysed larvae) of mouth deformities and a lack of functionality under 10 g L⁻¹ salinity. Transferring 2 DAH larvae from 33 g L⁻¹ (exhibiting normal mouth development) to a medium with a salinity of 10 g L⁻¹ had no effect on first feeding, weight and metamorphic index. Overall our results indicate the existence of a key time window (0–2 DAH) in which a salinity value higher than 10 g L⁻¹ is required to achieve adequate mouth development and further functionality of larvae. The present work represents a valuable contribution to the sole industry, opening new possibilities in hatchery management practices.