Evaluation of dissolved organic carbon levels in earthen ponds of common and grass carps and its relationships with water bacterial load, chlorophyll a, nutrients, and fish growth

This Study was conducted to evaluate dissolved organic carbon (DOC) and its relationship with bacterial load, chlorophyll a, nutrients, and fish growth in three larval ponds of common carp with areas of 3.5, 2.5, and 0.7 ha and three larval ponds of grass carp with areas of 0.7, 0.9, and 1 hectare located in Barardeh village, Sari city. Samples of water quality parameters such as temperature, oxygen, pH, DOC, nitrate, total nitrogen, ammonia, phosphate, bacterial, and chlorophyll a were taken weekly from 45 cm of water surface in inlet and outlet of the ponds. Regression relationships were then investigated between DOC and the studied parameters and fish biomass in the rearing ponds. The results showed that there were significant and non-significant relationships between the monthly averages of DOC and some nutrients such as nitrate, phosphate, and ammonia in inlets and outlets of the rearing ponds. The mean monthly DOC showed a significant relationship with the biomass values of common carp and grass carp, while its relationship with chlorophyll a content was significant in inlets but not in outlets of fishponds. In addition, DOC did not show a significant relationship with bacterial load in both common and grass carp ponds. Comparisions of physicochemical and biological parameters showed significant differences among months for some physicochemical parameters (p<0.05).