Habitat use and movement of hatchery-reared F2 Mekong giant catfish in the Mae Peum reservoir, Thailand, studied by acoustic telemetry

The horizontal and vertical movements of eight immature hatchery-reared (F2) Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in the Mae Peum reservoir, Thailand, from September to December 2005. All tagged fish were successfully monitored throughout the study period. All fish moved throughout the reservoir for approximately 1 month after release. Subsequently, their utilized areas became small, and the fish utilized deep areas of the reservoir. The fish displayed diel spatial movement patterns between deep areas in the day and shallow areas in the night. The vertical movements of the fish were related to the environment declination such as existence of hypoxic water and thermocline. Our results suggest that the establishment of a protected area in addition to conventional fisheries regulations may sustain the fish population in this reservoir.     

Protein and Energy Levels for Maximum Growth, Diet Utilization, Yield of Edible Flesh and Protein Sparing of Hybrid Clarias Catfish (Clarias macrocephalus×Clarias gariepinus)

Abstract— Two feeding trials were performed to determine dietary protein and energy levels for maximum growth, diet utilization, yield of edible flesh and protein sparing of hybrid Clarias catfish ( Clanas macrocephalus × Clarias gariepinus ). A 3 × 3 factorial design was employed for experiment 1 in which nine diets containing either 20, 30 or 40% protein and 275, 300 or 325-kcal digestible energy/100 g were used. The follow-up experiment 2 was a 3 × 2 factorial in which three protein levels (30, 35 and 40%) and two digestible energy levels (275 and 325 kcal/100 g) were tested. Dietary ingredients used in both studies were similar but the ratios of energy provided by dextrin and lard were 11.3/1.0 and 3.8/1.0 for experiments 1 and 2, respectively. Each of the experimental diets was fed to apparent satiation twice daily to three aquaria of fish (15 fish/aquaria) with average weight of 4.0 and 2.0 g for experiment 1 and 2, respectively, for 8 wk. Performance of fish in experiment 1 was mainly influenced by dietary protein rather than by energy levels. Maximum growth and diet utilization were attained at dietary protein and energy levels of 40% and 275 kcal/100 g, respectively. Energy levels did not spare dietary protein in experiment 1. In experiment 2, growth, diet utilization, and yield of edible flesh of fish were influenced by protein and energy levels. Furthermore, the protein sparing effect was observed in experiment 2. Best performance and protein sparing were found at 35% protein and 325-kcal digestible energy/100 g. The studies showed that dietary protein and energy requirement for hybrid Clarias catfish are affected by carbohydrate to lipid ratio. Fish utilize dietary energy with a dextrin to lard ratio of 3.8/1.0 more efficiently than that with a ratio of 11.3/1.0. Therefore, dietary protein and energy for best performance and protein sparing of hybrid Clarias catfish reported for experiment 2 were more appropriate.     

Horizontal and vertical movement of Mekong giant catfish <Emphasis Type="Italic">Pangasianodon gigas</Emphasis> measured using acoustic telemetry in Mae Peum Reservoir,Thailand

Abstract:   The horizontal and vertical movements of eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in Mae Peum Reservoir, Thailand between 2003 and 2004. The fish were monitored for between eight days and more than 9 months. All of the fish moved over the entire reservoir within approximately 40 days after release. Subsequently, the home range became small approximately 40 days after release. The fish preferred deep areas in the reservoir. The fish displayed diel horizontal and vertical movement patterns. The fish showed larger-scale horizontal movement during the daytime than at night. The fish repeatedly showed active vertical movement during the day, whilst there was little variation in swimming depth at night. Our results imply that the vertical movements of the fish were related to the environmental condition of the reservoir.     

Movements of immature hatchery-reared Mekong giant catfish <Emphasis Type="Italic">Pangasianodon gigas</Emphasis> released in the Mekong River,measured using acoustic telemetry

Twenty-eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas tagged with acoustic transmitters were released in the Mekong River, Thailand from 2002 to 2004. Twenty-four and four fish were tagged with normal transmitters and pressure-sensitive transmitters, respectively. Five to seven automated monitoring receivers were used for monitoring the post-release movements. The tagged catfish could be detected for up to 97 days, the first detection taking place at the release point, where the fish remained for several days. Sixteen tagged fish (57%) were not detected at any later point. These fish may have passed along the opposite (Laos) side of the river without notice because the width of the river was larger than the detection range of the transmitter. The remaining 12 tagged fish (43%) could be detected by the receivers installed, excluding the release point receiver. Of these 12 tagged fish, six showed long-distance (30–80 km) upstream movements and one long-distance (50 km) downstream movement. These seven fish (25%) were detected only during the daytime, suggesting that the Mekong giant catfish is diurnal.