Impact of Fish Cage Culture on Taal Lake (Philippines) Water and Sediment Quality as Assessed by Zebrafish Embryo Assay

Abstract

The present study investigated the impact of fish cage aquaculture on the quality of water and sediment samples from Taal Lake and the suitability of the contact assay using zebrafish (Danio rerid) embryos in assessing contamination levels in lakes. Fertilized zebrafish eggs were exposed to surface waters and whole sediments collected from three sites of varying levels of stress from Taal Lake, Philippines. Gonzales is the reference site, while Bafiaga and Balakilong are heavy aquaculture sites. Reconstituted water and artificial sand were used as negative controls while 2% ethanol was used as positive control. Mortality, abnormality and hatching rate within the 96 hour period were observed as endpoints of the study. No evident developmental differences were observed between the embryos exposed to the control and Taal Lake waters at the end of 96 hours, regardless of the site. Very high survival rates and hatching success rates were detected, and abnormalities were minimal and insignificant for the water samples. Sediments from Gonzales did not cause any detectable difference from the controls; however, significant embryotoxic responses were induced in embryos exposed to native sediments from Balakilong and Banaga. Survival rates were significantly reduced especially in the 75% and 100% sediment concentration and abnormality rates were also significant for the aquaculture sites. Hatching success rates were significantly reduced in Balakilong and Banaga sediments. The observed embryotoxic responses were discussed in relation to the presence of contaminants such as ammonia, copper, and lead which have settled in the sediments from unconsumed feeds. Results of the experiment clearly show that embryotoxic potential is associated with aquaculture sites and that fish cage culture has a negative impact on lake quality. Although the results of this experiment indicated satisfactory water quality, sediments from aquaculture sites were shown to be polluted with teratogens. This suggests a differential quality between Taal Lake surface waters and underlying sediments. The water is suitable for fisheries; however, sediments particularly those in Balakilong and Banaga pose a threat to the aquaculture industry especially during lake overturns. Based on the results, the 96-hour Zebrafish Early Life Stage Test is a practical and sensitive bioassay for assessing the impact of aquaculture on the water and sediment quality of Taal Lake.