Tolerance of Barbonymus schwanenfeldii under sulfide exposure

Hydrogen sulfide, a common occurrence in hydroelectric dam environment, is potentially toxic to living organisms in the environment. However, studies on the response of indigenous fish species when exposed to sulfide are still lacking in literature. Thus, behavioral responses and mortality of an indigenous fish species, Barbonymus schwanenfeldii, were determined in the laboratory where juveniles were exposed to different concentrations of sulfide. Three experiments were conducted during the exposure, namely, gradual sulfide exposure, sulfide exposure under lowering DO condition and gradual sulfide exposure under lowering pH condition. Methylene blue method was used to analyze the water for actual total sulfide concentrations. Behavioral responses, dissolved oxygen level and pH were taken and recorded. Four behavioral responses observed in sulfidic water were huddling, aquatic surface respiration, loss of equilibrium and mortality. However, in negative control no such responses were observed during the duration of the experiment. As the sulfide concentration increased, the time taken to the occurrence of behavioral responses decreased indicating increased toxicity. The LC50 at 6 h was estimated as 507.8 µg L -1 total sulfide (490 µg L -1 H2S) at 95% confidence level. Under sulfide exposure in lowering pH condition, mortality was significantly faster than the other two experimental conditions. This study shows that juveniles showed behavioral response to all sulfide concentrations tested and lowering both DO and pH levels increased the sulfidic toxicity as they led to faster mortality of juveniles. Key Words: huddling, aquatic surface respiration, loss of equilibrium, toxicity, mortality

Impacts of sulfide exposure on juvenile Tor tambroides (Bleeker, 1854): behavioral responses and mortality

Construction of hydroelectric reservoirs had been reported to be the cause of increased sulfide levels resulting from the decomposition of organic matter. As more dams are being built, a better understanding of the impact of sulfide on indigenous species is required. In Sarawak, Tor tambroides is a highly valuable and sought after species which is facing declining population. This study aimed to determine the behavioral responses and mortality of juvenile T. tambroides exposed to sulfide. The three exposure experiments were gradual sulfide exposure, gradual sulfide exposure under lowering DO and gradual sulfide exposure under lowering pH. A modified flow-through design was used to expose the juveniles in containers to sulfide of different concentrations. Actual total sulfide in containers was determined according to standard method. During the duration of the experiment, behavioral responses, DO and pH were monitored. Experimental results show that negative controls recorded no behavioral response and no mortality was observed in all control experiments. However, under all sulfide exposure experiments, the juveniles displayed at least one behavioral response in the progression of huddling together, aquatic surface respiration, loss of equilibrium and turning upside down except for the gradual sulfide exposure experiment where no response was observed with the lowest total sulfide concentration tested (82 µg L-1). For all three exposure experiments, faster responses and mortalities were observed when the concentration of sulfide increased. The LC50 at 6th hour of exposure was estimated to be 306 µg/L total sulfide (138 µg L-1 H2S) at 95% confidence level. Sulfide toxicity was found to be highly related to the decreasing DO and pH levels attributable to intensifying toxicity which led to mortality

Yellow Pufferfish of Batang Saribas, Sarawak

Yellow pufferfish or Xenopterus naritus (Tetraodontiformes: Tetraodontidae) is a brackish water or estuarine species. In Malaysia, the species can be found abundantly in the state of Sarawak and a well-known species in Batang Saribas, Sarawak from June to September. The species has economic value to the local people and ecological value on the mangrove and estuarine area of Batang Saribas. There are several studies that had been done on yellow pufferfish, but the molecular aspects of this species in Batang Saribas is still lacking. A total of 4 male yellow pufferfish were collected and examined. All the yellow pufferfish were yellowish in color and torpedo-like shape. The standard length was 14.85±0.191 cm and the total length was 18.33±0.583 cm. The number of soft dorsal fins was 31-33 and the soft anal fins were 26-27. Total DNA extraction using modified Doyle & Doyle (1987) was successful where only one individual showing pure DNA (OD260/OD230 ~1.80). The PCR of cytochrome b, Cytochrome Oxidase I and 16S RNA genes were still at optimization stage

Experimental study of mercury accumulation in juvenile cyprinid fish Barbonymus schwanenfeldii and Tor tambroides, exposed through water and feed

. This paper reports the experimental study of mercury accumulation in juvenile cyprinid fish of Barbonymus schwanenfeldii and Tor tambroides. The juvenile cyprinids were exposed to mercury (Hg) through water (0.5 mg/L and 1.0 mg/L) and feed (0.5 mg/kg and 1.0 mg/kg) for 30 days. The behavioral response during feeding was monitored over the experimental period. The Hg concentration in the juveniles was analyzed after 30 days. The juveniles exposed to water contaminated with 1.0 mg/L Hg was found to disperse upon feeding suggesting an increase in vulnerability towards threats. This however was not observed in other treatments through feed and at 0.5 mg/L Hg. In terms of survival percentage, no statistical difference was deduced between treatments for both species. Among the two species, T. tambroides demonstrated greater affinity of accumulation; this is likely due to its biological behavior as a fast swimming species. The uptake of Hg (II) through gills was more pronounce than that through ingestion as the diffusion of Hg(II) was inhibited by the mucosal lining in the latter pathway. No significant correlation was established between size and Hg concentration in juveniles of both specie