Optimizing grading frequency to enhance growth, survival, and size uniformity of GIFT tilapia fry in pond-based nursery systems

Abstract

Grading is a critical management practice in Genetically Improved Farm Tilapia (GIFT) nursery systems to reduce size variation, cannibalism and competition among fry. This study aimed to assess the effect of different grading frequencies on the growth performance, survival rate and size uniformity of GIFT fry reared in pond-based nursery systems. The pond had a surface area 56m2 surface area with a depth of 4 feet. The experiment was conducted in Aquaculture Development Centre Irnaimadu. over 30 days using four treatments: T1 (no grading), T2 (grading every 7 days), T3 (grading every 10 days) and T4 (grading every 14 days), each with three replicates. Fry were initially stocked at a uniform density and fed a commercial diet at 10% of their body weight. Parameters, including final weight, total length, survival rate and coefficient of variation (CV) for size uniformity were recorded and statistically analyzed. Results revealed that grading frequency had a significant (p<0.05) impact on all evaluated parameters. Fry in T2 showed the best performance, with a final average weight of 2.70 g, total length of 5.40 cm, survival rate of 92% and the lowest size variation (CV 12.5%). In contrast, ungraded fry (T1) recorded the poorest performance, with significantly lower weight, higher mortality and greater size disparity. The findings suggest that weekly grading effectively reduces size hierarchies and cannibalism, enhances feed access and promotes uniform growth and survival in GIFT tilapia fry. Longer intervals between grading or no grading increase competition and mortality. Therefore, implementing a 7-day grading interval is recommended for optimal fry performance and uniformity in pond-based nursery systems, particularly in small-scale aquaculture settings aiming for high survival and consistent growth. These insights contribute to improving nursery management strategies for sustainable tilapia farming.