Effects of Cobalt-60 Gamma Irradiation on the Malaysian Prawn Macrobrachium Rosenbergii.

A major obstacle in culture of the Malaysian prawn, Macrobrachium rosenbergii, is the complex social structure whereby a few large males dominate the population and reduce production. The goal of this work was to induce reproductive sterility by use of gamma radiation as a means to increase production. Of the 62 publications related to the use of gamma radiation in aquatic species published between 1938 and 1996, 66% did not indicate performance of dosimetry (dosage verification). Samples were not rotated during irradiation in 98% of these studies, which introduces considerable variation in dose. A dosimetric study in this dissertation found a 19% difference in dose rate for a 4-cm difference in height, and a 55% difference for a 4-cm difference in width. Sample rotation reduced variations to 14% vertically and 19% horizontally. Whether the surrounding medium was air or water could cause 218% variation at a particular location. Irradiation of larvae, postlarvae and juveniles showed that survival was inversely correlated with dose of gamma radiation. A dose of 3.0 krad resulted in total mortality within 9 days for larvae, and within 12 days for postlarvae and juveniles. The survival of male and female juvenile prawns exposed to gamma radiation was not different. Irradiation at 0.5 krad during the juvenile stage did not produce sterility. Survival was not significantly different from that of the non-irradiated group. Irradiation at 1.0 or 1.5 krad during the juvenile stage resulted in males with no sperm or reduced numbers of sperm. Females irradiated at 1.0 and 1.5 krad did not produce eggs or produced 35,000 eggs. Males irradiated at 1.0 or 1.5 krad were not able to fertilize the eggs of non-irradiated females. Non-irradiated males were not able to fertilize eggs of females irradiated at 1.0 and 1.5 krad. The achievement of sterile Malaysian prawns by irradiation at the juvenile stage with 1.0 and 1.5 krad of gamma radiation did not result in increased production

Assessing water quality of Murum Reservoir halfway through impoundment

This paper reports the water quality of Murum Hydroelectric Reservoir, eight months after impoundment of the dam. A total of nine stations were selected in the reservoir. Temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD5), chlorophyll-a and total suspended solids (TSS) were studied. The results showed that the water was warmer at 0.5 m depth. As the depth increased, temperature in the reservoir decreased in the range of 4.40°C to 7.35°C from 0.5 to 20 m depth. The concentration of DO dropped to zero at 4 - 6 m depth leading to anoxic level. pH at 0.5 m depth ranged from 6.40 to 7.20 and they were significantly higher (p<0.05) than those at 10 and 20 m. Chlorophyll-a at 0.5 m were in the range of 4.61 to 20.50 mg/L, relatively higher compared to 10 m and 20 m depths. The results obtained indicates that impoundment of Murum River generally caused water quality deterioration. In addition, this could be due to anthropogenic activities such as plantation and logging activities that are still going on within the catchment during the impoundment. Therefore, further continuous monitoring and investigation is required to determine the long-term water quality condition and identify factors that influence water quality in Murum Reservoir

Phosphorus in batang ai hydroelectric dam Reservoir, Sarawak, Malaysia

Phosphorus is the nutrient that is responsible for eutrophication in reservoirs and lakes. Batang Ai Hydroelectric Dam Reservoir has been used for aquaculture for 20 years. However, little information is available on phosphorus concentration in the reservoir. Therefore, in this study, different forms of phosphorus were determined at six stations. Results shows that concentrations of total phosphorus depends on the season whereby rainy season and high water level showed lower concentrations (24.90-38.59 μg/L) than dry season and low water level (45.94-67.28 μg/L). In addition, during dry season, near the aquaculture station in the reservoir, higher total phosphorus (67.3 μg/L) but lower dissolved total phosphorus (23.90 μg/L) and higher organic fraction (25.55 μg/L) and lower dissolved organic fractions (9.74 μg/L) were observed. The second highest total phosphorus was located upstream in Batang Ai during wet season and it was high in organic form attributable to grey and black water and domestic animal waste. Outflow total phosphorus showed higher concentration during dry than wet season and it was much higher in dissolved organic form than dissolved reactive form. During dry season, outflow total organic phosphorus was twice the inflow but during wet season, the opposite was observe

Hydrodynamic Modeling of a Tropical Tidal River Using the Dynamic Estuary Model (DYNHYD5): A Case Study in Sibu Laut River, Sarawak, Malaysia

Application of the Dynamic Estuary Model (DYNHYD5) in a tropical tidal river is limited. The successfully calibrated and validated hydrodynamic model is valuable in subsequent water quality simulation for environmental management. Hence, a hydrodynamic modeling approach using the DYNHYD5 was conducted in a tropical tidal river in Malaysia. Samplings were conducted in the Sibu Laut River to collect the hydrology data for model simulation. The model was calibrated and validated by comparing the simulated flow and mean depth with the field data at different simulation periods of time. The results showed that the model DYNHYD5 was successfully calibrated with channel flows and mean depths and then reproduced with good agreement in validation. The observed and simulated data were linearly correlated (R2 > 0.8) with values of slope γ ranging from 0.891 to 1.204 in both calibration and validation. The Nash–Sutcliffe coefficient of efficiency (NSE) of more than 0.7 in both calibration and validation also indicated satisfactory comparison between the observed and simulated data. The result indicated that the application of the DYNHYD5 is feasible in a tropical tidal river in Malaysia

Assessment of water quality of Batang Rajang at Pelagus Area, Sarawak, Malaysia

This study was carried out to examine the water quality of Batang Rajang at Pelagus area, Sarawak, Malaysia. Water quality was determined at 12 stations along Batang Rajang and its tributaries in terms of in-situ and ex-situ water quality parameters. The results showed that most stations at main river were categorized as slightly polluted while most tributaries were clean according to the Water Quality Index. The river is suffering from organic pollution where almost all stations along the river contained high chemical oxygen demand (≈ 43.1 mg/L) and total ammonia nitrogen (≈ 0.520 mg/L) and were classified as Class III and IV at most of the stations. High suspended solids (218.3 mg/L) and low dissolved oxygen (4.6 mg/L) were observed at the main river. The low dissolved oxygen content from the Bakun dam upstream of the study area has an impact on the river particularly during dry season where DO dropped below the minimum required for sensitive aquatic organisms. As seven tributaries are within Class II indicating healthy freshwater ecosystems, they should be conserved as habitats for sensitive aquatic organisms. Conversely, proper management need to be initiated in particular, Sungai Merit tributary and the main river where DO were below the minimum required for sensitive aquatic organisms

Impact of Different Land Uses on the Escherichia coli Concentrations, Physical and Chemical Water Quality Parameters in a Tropical Stream

Rural streams are important source of water for the nearby communities. However, bacterial contamination from agriculture and human settlement may render the water unsuitable for drinking and body contact recreation. Hence, the objective of this study was to determine the impact of different land uses such as animal farming and human settlement on E. coli concentrations in the Serin River, a tropical stream. Samplings were conducted at 9 stations from September 2009 to March 2010. Results showed that E. coli concentrations ranged from 2,000-6,900,000 CFU/100 mL with E. coli concentrations in fish aquaculture water exceeding the WHO standard. Animal and crop farming stations showed the highest E. coli concentrations in the tributaries. Re-suspension from stream sediment and non-point sources such as runoff contributed to the high concentrations observed in the main river. Multiple linear regressions indicated that total suspended solids and dissolved oxygen were significant water quality parameters and they explained 68.1% of the total E. coli variations observe

Baseline trace metals in water and sediment of the Baleh River—a tropical river in Sarawak, Malaysia

Quantitative indices are classically employed to evaluate the contamination status of metals with reference to the baseline concentrations. The baselines vary considerably across different geographical zones. It is imperative to determine the local geochemical baseline to evaluate the contamination status. No study has been done to establish the background concentrations in tropical rivers of this region. This paper reports the background concentrations of metals in water and sediment of the Baleh River, Sarawak, derived based on the statistical methods where the areas possibly disturbed are distinguished from the undisturbed area. The baseline levels of six elements in water determined were Al (0.34 mg/L), Fe (0.51 mg/L), Mn (0.12 mg/L), Cu (0.01 mg/L), Pb (0.03 mg/L), and Zn (0.05 mg/L). Arsenic and selenium were below the detection limit. For sediment, the background values were established according to statistical methods including (mean + 2σ), iterative 2σ, cumulative distribution frequency, interquartile, and calculation distribution function. The background values derived using the iterative 2σ algorithm and calculated distribution function were relatively lower. The baseline levels calculated were within the range reported in the literatures mainly from tropical and subtropical regions. The upper limits proposed for nine elements in sediment were Al (100,879 mg/kg), Cr (75.45 mg/kg), Cu (34.59 mg/kg), Fe (37,823 mg/kg), Mn (793 mg/kg), Ni (22.88 mg/kg), Pb (27.26 mg/kg), Zn (70.64 mg/kg), and Hg (0.33 mg/kg). Quantitative indices calculated suggest low risk of contamination at the Baleh River

FISHES

The Pelagus area is located in the middle stretches of Batang Rajang, in the central part of Sarawak, under the administrative division of Kapit. The area is well-known for its long and dangerous rapids that extend for a distance of 12.8 km. Over the years, these “rapids of death” have capsized many boats along its treacherous and unpredictable waterways. To determine the fish composition in the Pelagus area, three study sectors were sampled, namely, Nanga Benin, representing the downstream area; Nanga Peraran, the midstream area; and Punan Bah, which represents the upstream areas. At each sector, sampling stations were established along the Batang Rajang and its tributaries (Fig. 1; Table 1). Field sampling was conducted in April and August of 2014, as well as January and July of 2015. Fishing methods applied include gill nets of various mesh sizes (2.5 cm, 3.81 cm, 5.08 cm, 7.62 cm and 10.16 cm), 3-layered nets, cast nets (Fig. 2–3) and electro-shocking. Similar fishing efforts were employed at the different stations (Fig. 4) and at other study sectors. Fishes caught were mostly identified in the field (Fig. 5), but others were brought to the laboratory for further study