Seasonal variations in water quality of a tropical reservoir: Considerations for cage aquaculture expansion

A study of water quality of the 30 year-old Batang Ai hydroelectric reservoir at different depths and locations was conducted to give a better understanding of the water quality status for aquaculture expansion. The study was conducted at four locations where two were identified as potential cage culture sites but nearby current operations. Temperature and dissolved oxygen (DO) profilings and 13 other parameters at 0.2, 10 and 20 meters depths were also studied. It was found that the difference in DO between seasons were significant. Pockets of high nutrients and hydrogen sulphide were observed at 10 and 20 m nearby the two cage culture sites in dry season. Additionally, regardless of season, those sites showed significantly higher 10 m and 20 m suspended solids. At one of the locations near cage culture, dry season total phosphorus and ammonia were the highest at all depths and chlorophyll-a was at eutrophic level at 10 m depth. All these are attributed to aquaculture waste, pre-marketing fish processing and the lack of mixing. Water Quality Index shows that the 0.2 m depth is suitable for sensitive aquatic organism. However, dry season 10 m water column of the two potential cage culture sites was polluted. Though the cages do not normally extend to 10 m deep, when overturn occurs, it could cause fish kills. Thus, in reservoir cage culture, elimination of reservoir pre-market processing is crucial and considerations have to be made on the proximity to the current operations and dry season water quality limitations. © 2018, BIOFLUX SRL. All Rights Reserved

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

Changes in Water and Sediment Quality of a River Being Impounded and Differences Among Functional Zones of the New Large Tropical Hydroelectric Reservoir

Though more large tropical reservoirs are being constructed to meet the increasing energy demand, knowledge on the impact of damming a tropical river and the differences along the river after its impoundment is scarce. Thus, the present study aimed to increase our understanding of such differences both longitudinally and vertically. Water and sediment samples were collected at three different functional zones in the Murum River basin 10 months after impoundment began. Results show that the impoundment has an impact on both the water and sediment. Longitudinal variations of water and sediment characteristics were observed at different functional zones. The upstream riverine zone subjected to anthropogenic activities serves as the main input of suspended solids and nutrients to the reservoir. The nitrogen changed from a high nitrate and low ammonia condition prior to impoundment to a low nitrate and high ammonia condition due to the accumulation of organic matter and slow nitrification rate after impoundment. In the transitional and lacustrine zones, vertical stratifications of dissolved oxygen and temperature were observed. The thickness of a well-oxygenated column for sensitive aquatic organisms was only 2 m at some stations. Water quality in all zones showed impairment during the filling phase as compared to the good water quality index before impoundment. The reduction of suspended solids in the surface water column in the transitional and lacustrine zones is a positive change for aquatic organisms. Sediment characteristics were found to be distinct in the transitional zone, where it was lower in sand and higher in silt, clay, organic carbon and nutrients in contrast to the riverin

Fish assemblages, growth pattern and environmental factors in Upper Baleh River, Kapit, Sarawak

A survey of the freshwater fish composition in the upper Baleh River, Sarawak was conducted in 2015. A total of 1,538 specimens, comprising 45 species from ten families were collected using electrofishing devices and cast nets. The family Cyprinidae was the most dominant (62.9%) as well as diverse (42.2%) family, followed by the Gastromyzontidae (30.4%; 22.2%) in the river. The three most dominant species were Tor tambra (18.1%), Lobocheilos ovalis (12.9%), and Parhomaloptera microstoma (11.3%). Shannon’s diversity index, Margalef’s richness index, and Pielou’s evenness index were 2.9, 6.0, and 0.8, respectively, an indication of moderate species diversity. Canonical Correspondence Analysis demonstrate that elevation, stream order and sedimentation were the most significant factors related to fish assemblages in the river, particularly for members of the families Cyprinidae and Gastromyzontidae. The coefficient ‘n’ value in length-weight relationship for Tor tambra, Lobocheilos ovalis, and Parhomaloptera microstoma were determined as 2.92, 2.72, and 3.15, respectively. Tor tambra and Lobocheilos ovalis exhibited a negative allometric growth pattern which could be due to food competition whereas Parhomaloptera microstoma exhibited a positive allometric growth pattern as mountainous forest stream habitat offers favourable environmental conditions. The Fulton’s condition factor of each species indicates that Tor tambra and Lobocheilos ovalis were in poor condition, whereas Parhomaloptera microstoma was in extremely poor condition. It is hypothesized that environmental degradation caused by logging activities have affected the health of the most dominant fish species in the upper Baleh River. Further study should be conducted to determine the underlying factors that are affecting the fish diversity

Effects of water temperature, dissolved oxygen and total suspended solids on juvenile barbonymus schwanenfeldii (Bleeker, 1854) and Oreochromis Niloticus (Linnaeus, 1758)

The aim of the present study was to investigate the effects of water temperature, dissolved oxygen (DO), and total suspended solids (TSS) in water on an indigenous fish species, Barbonymus schwanenfeldii (Bleeker, 1854), and an exotic fish species, Oreochromis niloticus (Linnaeus, 1758) in Malaysia. The survival rate, growth performance, and feed conversion ratio (FCR) of juvenile fish were tested in different water quality conditions for 30 days. The water temperature of 30°C, DO value of less than 4 mg L-1, and TSS content of 1000 mg L-1 are believed to be harmful to fish life. The result indicates that the O. niloticus juveniles are relatively tolerant of high water temperature and TSS in term of survivorship, whereas the B. schwanenfeldii juveniles are more vulnerable to the two parameters. Reduced DO value had influenced the survival rate of both fish species in a similar way where 100% mortality of both fish species occurred at DO value less than 2 mg L-1. The growth performance of juvenile B. schwanenfeldii was less susceptible to the changes of water temperature and DO whereas the growth performance of juvenile O. niloticus was influenced by the two parameters. The results show that the FCR of both fish increased with high water temperature and TSS. The juvenile B. schwanenfeldii was able to sustain its growth by consuming additional food in high water temperature. Increased DO value significantly improved the FCR of O. niloticus juvenile but not of B. schwanenfeldii juvenile. © 2018, BIOFLUX SRL. All Rights Reserved

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