Mon, Aug 15, 2022: 3:30 PM-3:45 PM
513D
Background/Question/MethodsRecycling inorganic nutrients that sunk to profundal zone is important to increase primary production in an aquatic ecosystem. However, in a reservoir, there has been limited information on vertical transportation of inorganic nutrient generated in anoxic hypolimnion zone to higher trophic levels in oxygenated limnetic zone. The objective of our study was to trace uptake of reduced compound by consumers using multiple stable isotopes (carbon [δ13C], nitrogen [δ15N], and sulfur [δ34S]) and the composition of fatty acids (FAs). Here, we expected the striped catfish (Pangasianodon hypophthalmus) rely on reduced compound in a reservoir due to its high hypoxia tolerance. In the Kaeng Krachan Reservoir, western Thailand, we collected muscle samples of the catfish (n = 25 for juvenile [37–50 cm in total length]; n = 11 for adult [80–106 cm in total length]) for stable isotope and FA composition analysis. δ13C and δ15N of periphyton and particulate organic matter (POM) were used as an endmember of photoautotrophs. Using δ34S, we inferred a use of organic matter derived from anoxic zone and/or oxic-anoxic interfaces in the catfish. In addition, we determined the FA composition of the catfish to estimate the origin of organic matter (algae vs. bacteria).
Results/ConclusionsThe striped catfish in the reservoir represented the different isotopic signatures and FA composition between adult and juvenile. For the adult catfish, δ13C value were intermediate between periphyton and POM, while the δ15N value was higher than that of periphyton and POM. The adult catfish also contained more algae-specific FAs than bacteria-specific FAs, suggesting that they were feeding on photoautotrophs. On the other hand, the juvenile catfish showed lower δ13C and δ15N than that of periphyton and POM, suggesting that it used alternative sources of autochthonous organic matter as well as photoautotrophs. The juvenile catfish exhibited lower δ34S value than δ34S–sulfate of water column is likely to be influenced by sulfide. The juvenile catfish was characterized by rich bacterial FAs more than algal FAs. Our findings suggest that inorganic matter pooled in an anoxic zone is converted to organic matter via chemosynthetic bacteria and then consumed by the juvenile catfish. Overall, inorganic nutrient matters derived from the anoxic hypolimnion zone may indirectly support the production of consumers at the oxidation environment in a reservoir.
Results/ConclusionsThe striped catfish in the reservoir represented the different isotopic signatures and FA composition between adult and juvenile. For the adult catfish, δ13C value were intermediate between periphyton and POM, while the δ15N value was higher than that of periphyton and POM. The adult catfish also contained more algae-specific FAs than bacteria-specific FAs, suggesting that they were feeding on photoautotrophs. On the other hand, the juvenile catfish showed lower δ13C and δ15N than that of periphyton and POM, suggesting that it used alternative sources of autochthonous organic matter as well as photoautotrophs. The juvenile catfish exhibited lower δ34S value than δ34S–sulfate of water column is likely to be influenced by sulfide. The juvenile catfish was characterized by rich bacterial FAs more than algal FAs. Our findings suggest that inorganic matter pooled in an anoxic zone is converted to organic matter via chemosynthetic bacteria and then consumed by the juvenile catfish. Overall, inorganic nutrient matters derived from the anoxic hypolimnion zone may indirectly support the production of consumers at the oxidation environment in a reservoir.