Primary Productivity of Phytoplankton,Environmental Covariates and Fish Growth in West Bengal Ponds under a Polyculture System

Measurements of primary production by phytoplankton in four fish ponds over a period of one year revealed a distinct spatial variation in rate. The ponds were used for polyculture, monoculture, or a traditional system of fish culture. The rates of gross photosynthesis were highly correlated with temperature, free CO₂, oxygen, inorganic nitrogen (NH₄⁺, NO₂⁻, and NO₃⁻) and PO₄-P. It was shown by step-wise multiple regression analysis that in the polyculture pond with a predominantly autotrophic metabolism, gross photosynthesis was the most significant factor correlated with fish growth. In another polyculture system in which the metabolism was mainly hetero-trophic, the influence of the photosynthesis rate was slight.