Tolerance of fry of three tilapia varieties exposed to low temperatures

As tilapia aquaculture expands globally, cold sensitivity remains a critical issue, leading to significant losses due to poor growth, disease susceptibility, and high mortality. This study evaluated the cold tolerance in fry of three tilapia varieties, incorporating a comprehensive analysis of 3240 specimens. The fry, segregated by variety into different tanks, were observed during summer to assess their performance. The study focused on two commercially prominent varieties, known for their rapid weight gain, and a third variety developed by the Federal University of Lavras, specifically bred for resilience to local climatic conditions. Following a 15-day acclimation period in experimental tanks, the fry were monitored for feeding to apparent satiety. Daily assessments included counting mortalities and measuring water temperature and dissolved oxygen levels. Survival data were analyzed using multivariate Cox regression, with survival curves derived via the Kaplan-Meier method. Lifespan predictions from these curves were compared using the log-rank test. Results indicated that older fry were more resilient to cold stress. Notably, the MGTUP variety, bred for local environmental adaptability, demonstrated superior cold tolerance. This variety also exhibited the lowest mortality rates across all age groups. These findings suggest that utilizing locally adapted tilapia varieties can significantly mitigate losses in aquaculture, especially in cold-prone regions.