Cold snaps in Indian coastal waters: a critical threat to nursery rearing of juvenile silver pompano (Trachinotus blochii) in marine cages

The impact of sea surface temperature (SST) anomalies on juvenile silver pompano (Trachinotus blochii) survival was assessed. Juveniles (2.4–2.6 cm; 2000 fish) were transported in oxygenated packs (12 fish L⁻¹) for 26 h and stocked in a marine cage farm on October 2, 2022. An initial mortality of silver pompano juveniles (29%) occurred immediately after stocking, followed by mass mortality from October 10 to 14. SST anomaly studies revealed the presence of colder coastal waters in 2022 compared to 2021, with satellite data showing a negative SST anomaly along India’s west coast during October and November. In situ data recorded a significant SST drop from October 3 to 7, stabilizing briefly before declining for the rest of the month, correlating with mortality patterns. Positive sea level anomalies (SLA) observed on October 1 transitioned to negative SLA by October 3, indicating a shift from downwelling to upwelling, resulting in coastal water cooling. To confirm the effect of acute temperature reduction, juveniles were subjected to two treatments: normal seawater temperature (28 °C) and reduced temperature (23 °C) for 2 to 6 h. In the reduced temperature treatment, 40% of silver pompano juveniles died within 120 min, demonstrating that sudden temperature drops significantly increase mortality risk in juvenile pompano. The study warns that drastic changes in SST can negatively impact marine fish nursey rearing and aquaculture sustainability. The findings emphasize the critical need for temperature forecasting and management to mitigate risks in coastal fish rearing.