Assessment of Water Quality Parameters and their Relationship with Weight Gain of Common Carp (Cyprinus carpio L .) in an Iraq Aquaponic System

Abstract

Aquaponics is an eco-friendly and sustainable method that combines plant cultivation and fish rearing into a single, integrated system. Fish waste is naturally recycled by the system and transformed into nutrients that plants may readily absorb by helpful bacteria. Three aquaponic systems, which are closed systems, fish culture common carp (Cyprinus carpio((. with hydroponic plant production pepper (Capsicum spp.) and tomato (Solanum lycopersicum) were used in the 105-day trial, which ran from December 2024 to April 2025. The objective of this study was to evaluate selected physical and chemical water quality parameters and to examine their relationship with the weight gain of common carp (C. carpio(. The results indicated that dissolved oxygen concentrations remained within the recommended limits throughout the experimental period. Nitrate concentrations were also maintained within the acceptable ranges for fish during the entire study. Electrical conductivity values were higher than the recommended limits, while pH values remained within the acceptable range for both fish and nitrifying bacteria. Furthermore, the results revealed a highly significant correlation between fish body weight and electrical conductivity as well as water temperature, in addition to a highly significant correlation between electrical conductivity and water temperature. An evaluation of the water quality provides a comprehensive understanding of the interactions and balance between fish, plants, and microorganisms in aquaponic systems. The study results showed that fish growth and bacterial efficiency are significantly affected by five water quality commonly measured in aquaponic systems: dissolved oxygen, pH, water temperature, nitrate concentration, and electrical conductivity.