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.
