Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

Abstract

A feeding trial was performed in the laboratory with the catfish species Pterygoplichthys disjunctivus to determine stable carbon ( 13 C) and nitrogen ( 15 N) turnover rates and discrimination factors in non-lethally sampled tissues (red blood cells, plasma solutes, and fin). A second feeding trial was conducted to determine what P. disjunctivus could assimilate from low-quality wood-detritusrefractory polysaccharides (e.g., cellulose), or soluble wood-degradation products inherent in wood-detritus. This was performed by feeding the fish an artificial wood-detritus diet with fibrous (δ 13 C=−26.36‰; δ 15 N=2.13‰) and soluble portions (δ 13 C=−11.82‰; δ 15 N=3.39‰) that had different isotopic signatures and monitoring the dynamics of isotopic incorporation in the different tissues over time. Plasma solutes turned over more quickly than red blood cells for 13 C and 15 N. However, in contrast to previous studies of juvenile fishes, C and N incorporation was primarily driven by catabolic tissue turnover as opposed to growth rate. Tissue-diet discrimination factors for 15 N varied from 4.08 to 5.17‰, whereas they were <2‰ for 13 C (and less than 0.3‰ for plasma and red blood cells). The results of trial two suggested that P. disjunctivus could not assimilate refractory polysaccharides. Moreover, the δ 13 C and δ 15 N signatures of wild-caught P. disjunctivus from Florida confirmed their detrital trophic standing in Floridian aquatic ecosystems.

Slow Isotope Turnover Rates and Low Discrimination Values in the American Alligator: Implications for Interpretation of Ectotherm Stable Isotope Data

“…In contrast, reptile plasma and RBC tissues can display short estimated complete turnover rates (e.g., 19 d for Caretta caretta; table 2) but also much longer rates (e.g., 1,109 d for Alligator mississippiensis; table 2) that have never been found in endotherms. Other ectotherms display patterns similar to those in reptiles in terms of estimated complete isotope turnover rates for RBCs and plasma, with fishes (including sharks) displaying widely varying rates that range from 11 to 432 d (Buchheister and Latour 2010;German and Miles 2010;Logan and Lutcavage 2010;Kim et al 2012). These trends suggest that isotope turnover rates in ectotherms can be relatively fast in some species and even comparable to rates observed in endotherms but that isotope turnover rates in other ectotherm species can also be orders of magnitude slower than those in endotherms.…”

A comparison of changes in stable isotope ratios in the epidermal mucus and muscle tissue of slow‐growing adult catfish

“…However, isotope ratios in the muscle tissues of fishes cannot detect such short-term diet shifts, particularly when slow-growing fishes are of interest. To the best of our knowledge, the most rapid isotopic change in the tissues of fishes was observed in the blood plasma of armoured catfish, Pterygoplichthys disjunctivus C.Weber, with a mean residence time estimated to be 11 and 33 days for δ 13 C and δ 15 N values respectively (German & Miles, 2010). This slow response is considered to be due to slow growth rates in most adult fishes compared with those in some organisms at lower trophic levels, such as crustaceans and algae (Fry & Arnold, 1982), and low catabolic turnover rates compared with those in endothermic animals (Tieszen, 1983).…”

Isotopic variation among Amazonian floodplain woody plants and implications for food-web research

“…Although unrealistic, we included models without isotopic variation of sources (SD ¼ 0) to demonstrate the various effects of isotopic variation on model results as other popular software packages build mixing models on mean values without accounting for variation (e.g., IsoSource, Phillips & Gregg 2003). Fractionation values used in mixing models (N ¼ 4.39 ± 0.05; C ¼ 0.06 ± 0.08) follow those in German & Miles (2010) calculated from plasma of a tropical herbivorous fish.…”