Striped catfish (Pangasianodon hypophthalmus) exploit food sources across anaerobic decomposition- and primary photosynthetic production-based food chains

Dietary information from aquatic organisms is instrumental in predicting biological interactions and understanding ecosystem functionality. In freshwater habitats, generalist fish species can access a diverse array of food sources from multiple food chains. These may include primary photosynthetic production and detritus derived from both oxic and anoxic decomposition. However, the exploitation of anoxic decomposition products by fish remains insufficiently explored. This study examines feeding habits of striped catfish (Pangasianodon hypophthalmus) at both adult and juvenile stages within a tropical reservoir, using stable carbon, nitrogen, and sulfur isotope ratios (δ¹³C, δ¹⁵N, and δ³⁴S, respectively) and fatty acid (FA) analyses. The adult catfish exhibited higher δ¹⁵N values compared to primary consumers that feed on primary photosynthetic producers, which suggests ingestion of food sources originating from primary photosynthetic production-based food chains. On the other hand, juvenile catfish demonstrated lower δ¹⁵N values than primary consumers, correlating with low δ³⁴S value and large proportions of bacterial FA but contained small proportions of polyunsaturated FA. This implies that juveniles utilize food sources from both anoxic decomposition and primary photosynthetic production-based food chains. Our results indicate that food chains based on anoxic decomposition can indeed contribute to the dietary sources of tropical fish species

Feeding habits of hatchery-reared young Mekong giant catfish in a fish pond and in Mae peum reservoir

Organized by Graduate School of Informatics, Kyoto University ; JSPS Bangkok Liaison Office ; Japanese Society of Bio-logging Science ; Informatics Research Center for Development of Knowledge Society InfrastructureDecember 13-14, 2005, Siam City Hotel, Bangkok, ThailandWe studied the feeding habits of the hatchery-reared young Mekong giant catfish released in a fish pond and Mae peum reservoir, northern Thailand. We examined the gut (stomach and intestine) contents of 5 catfish, Relative Length of Gut (RLG) of 4 catfish and plankton composition in the reservoir. The gut contents of the catfish in the fish pond consisted of a fluid like the pellets, zooplankton, phytoplankton and aquatic plants. The gut contents in the reservoir consisted of unspecified contents, zooplankton and phytoplankton. The majority of prey items were the Branchiopoda (75 % in zooplankton) and Chlorophyceae (98 % in phytoplankton) in the gut contents of the catfish in the reservoir, while the major plankton in the reservoir were copepoda including nauplius and copepodid (mean : 50 %) and eurotatorea (mean : 41 %) in zooplankton, and chrysophyceae (mean : 52 %) and chlorophyceae (mean : 38 %) in phytoplankton. It is reasonable to suppose that the catfish positively selected their major prey items if a particular prey item was found in the gut contents, contrary to the organism composition in the reservoir. However, the cuticle and the cell walls of these plankton are resistant to intestine enzymes of some fish. Furthermore, RLG of 4 catfish were greater than 1. In general, a fish is carnivorous when RLG is less than 1, while the fish is herbivorous or omnivorous when RLG is greater than 1. These results indicate that the hatchery-reared young catfish fed on the potential prey items in front of the catfish, and the catfish might not be piscivorous but planktivorous

Study on the behavior of F2 Mekong giant catfish using ultrasonic telemetry

Organized by Graduate School of Informatics, Kyoto University ; JSPS Bangkok Liaison Office ; Japanese Society of Bio-logging Science ; Informatics Research Center for Development of Knowledge Society InfrastructureDecember 13-14, 2005, Siam City Hotel, Bangkok, ThailandThe Department of Fisheries, Ministry of Agriculture & Cooperatives of the Thai government first succeeded in producing a second generation (F2) of Mekong giant catfish Pangasianodon gigas through artificial insemination in 2001. In order to compare the behavior of F2 catfish with those of the first generation (F1), we monitored ten F2 catfish for 18 days using ultrasonic telemetry in an artificial reservoir (Mae Peum reservoir, Phayao province, Thailand). The F2 catfish stayed shallower at night and deeper during the day, and avoided hypoxia areas of the reservoir. Since this diel vertical movement was observed in the previous study on F1 catfish, F2 catfish should be as behaviorally healthy as F1 catfish