Effects of Selected Water Quality, Sulfide and Mercury on Juveniles Barbonymus schwanenfeldii and Tor tambroides

Azimah, Apendi (2018) Effects of Selected Water Quality, Sulfide and Mercury on Juveniles Barbonymus schwanenfeldii and Tor tambroides. Masters thesis, Universiti Malaysia Sarawak(UNIMAS).

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Abstract

Alterations of dissolved oxygen (DO), total suspended solids (TSS), temperature and pH could affect the growth and survival of fishes. Hydrogen sulfide and mercury, both under high concentrations are toxic and lethal to the aquatic organisms. In Sarawak, creation of new hydroelectric reservoirs results in changes in DO, TSS, temperature and pH with increasing sulfide and mercury. Freshwater fish species, Barbonymus schwanenfeldii and Tor tambroides have important economical values and act as a protein source to human. Both species require an optimum condition to survive in the nature and the changes in natural aquatic habitat due to anthropogenic activities lead to the reduced quantity and quality of these two indigenous species. This study aimed to determine the mortality and behavioral responses of both species to changes in water quality parameters, changes in the level of hydrogen sulfide and exposure to mercury in water and feed. In the water quality experiment, both species were exposed to 25 different combinations of temperature, TSS, pH and DO at three different levels, in 30 days’ period. Response surface methodology was used to optimize the best set of condition for both species to survive. The results of this study show that avoidance when fed and longer feeding time were observed by both species in experiments with TSS higher than 1000 mg/L. Suspended solids in water reduced the visibility of fishes and affected their feeding activity. B. schwanenfeldii was predicted to survive the best under the combination of 27 °C, 0 mg/L TSS, 4.8 mg/L DO and pH 7.04 whereas the best set of condition for T. tambroides to survive are 23.9 °C, 0 mg/L TSS, 4.5 mg/L DO and pH 7.02. Sulfide tolerance was determined in 15 L containers with freshwater (100 mL/min) and sulfide stock solutions (5 mL/min) supplied. Methylene blue method was used to analyze the water for total sulfide concentration which was used to plot LC50. Four behavioral responses were observed namely, huddling together, aquatic surface respiration, iv loss of equilibrium and turned upside down. The responses were observed earlier for higher sulfide concentration compared to the lower sulfide concentrations. The LC50 of B. schwanenfeldii at 6 h was found to be 507.8 μg/L at 95% confidence level whereas for T. tambroides was 306.1 μg/L at 95% confidence level. Under this condition, the fish reached 100% mortality as early as 6 h at concentration 659 ± 39 μg/L and 50% mortality was earliest at 5 h at the same concentration. Lowering pH and dissolved oxygen levels were proven to aggravate sulfide toxicity. The adsorption of mercury through water was determined by exposing the fishes to mercury-spiked water while for adsorption through feed was done by feeding with mercury-spiked feed. Both experiments were carried out in 30 days. The concentrations of mercury in fish was determined by microwave assisted digestion then analyzed by mercury analyzer. In the mercury toxicity experiment, both B. schwanenfeldii and T. tambroides exhibited avoidance when fed and time taken to feed was also longer. Exposure of mercury through water exhibited higher survival rate for both species compared to feed exposure. However, the mercury concentration in both species’ tissue were higher in water exposure than feed exposure experiment. In general, the experiments carried out show that changes in water quality parameters, hydrogen sulfide levels and exposure to mercury affected the mortality and behavioral responses of both species.

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