Status of Fish Assemblages in Four Major Reservoirs of Thailand

Fish assemblage status is essential information for practical fishery resource management in productive water bodies. This study aimed to assess fish assemblages’ status and provide recommendations for practical fishery management in four major reservoirs in Thailand. Night-time samples were collected between January 2015 and December 2019 using gill net with multiple mesh sizes. Results obtained through univariate and multivariate analyses showed that the Pa Sak Jolasid Reservoir had the highest number of fish species (70), while the Rajjaprabha Reservoir had the lowest number (41). Eight species were identified as in danger of extinction and six species as alien. The percentage of the index of relative importance (% IRI) showed that the major species mainly belong to the family Cyprinidae. The forage and carnivorous fish ratio (F/C ratio) showed balanced communities in all reservoirs (4.4–9.2) except the Sirikit Reservoir (1.0). The evenness index (J') (0.53–0.67) and diversity index (H') (1.86–2.38) indicated moderate diversity and distribution in all reservoirs. Catch per unit effort (CPUE) value displayed a medium abundance in the Sirikit and Ubolratana Reservoirs (614.8 and 826.0 g.100 m-2 of gill net/night, respectively), and a high abundance in the Rajjaprabha and Pa Sak Jolasid Reservoirs (1,087.2 and 1,012.5 g.100 m-2 of gill net/night, respectively). In the overall assessment of fish assemblage status among the reservoirs, the Pa Sak Jolasid and Rajjaprabha Reservoirs showed the most desirable condition, while the Sirikit Reservoir showed the least desirable condition. These findings suggest the need to implement various practical fishery resource management, such as banning the introduction of invasive exotic species, and establishing conservation measures for species on the list of extinction