Effect of Zinc Application on Phytoplankton Productivity, Survival and Growth of Fry and Fingerlings of Rohu (Labeo rohita H.)

Abstract

Aims: The present study aims to evaluate the role of zinc (Zn) supplementation in enhancing plankton productivity and its subsequent effects on the survival, growth, haematological health, and innate immune response of Labeo rohita (rohu) fry and fingerlings. Study Design: Laboratory-based microcosm and outdoor tank-based mesocosm experiments were conducted with varying Zn concentrations. Place and Duration of Study: The experiments were carried out at Indian Council of Agricultural Research-Central Institute of Freshwater Aquaculture (ICAR-CIFA), Bhubaneswar, Odisha, India, over a multi-phase research during the year 2022. Methodology: The initial laboratory trials used different Zn concentrations (0.00 to 2.00 mg/l) to study plankton biomass and chlorophyll-a content under controlled photo-bioreactor conditions, with and without Zn top-dressing. Based on the outcomes, two follow-up studies were conducted to evaluate the impact of Zn on rohu fry and fingerlings using lower Zn concentrations (0.00 to 0.50 mg/l) in 100–1500 L FRP (Fiberglass Reinforced Plastic) and concrete tanks. The study assessed survival, growth performance, blood parameters (Hb, PCV, RBC/WBC counts), and innate immunity (respiratory burst and myeloperoxidase activity). Results: Zinc supplementation up to 1.00 mg/l significantly improved plankton productivity, particularly under top-dressed conditions. However, higher Zn concentrations negatively impacted survival and growth of rohu fry, indicating potential toxicity. Further, lower Zn levels (0.10 mg/l), enhanced survival, weight gain, and length in both fry and fingerlings. Moreover, Zn at 0.10 mg/l significantly improved haematological parameters and innate immune markers without adverse effects. Conclusion: The findings clearly establish that Zn at an optimal concentration of 0.10 mg/l enhances primary productivity, promotes healthy growth, and strengthens the immune system of rohu, Labeo rohita. This study suggests that regulated Zn supplementation can be a sustainable strategy for improving freshwater aquaculture productivity while minimizing environmental and physiological risks.