Carbon, nitrogen and phosphorus ecological stoichiometry of Lateolabrax macultus and Acanthogobius ommaturus in the Estuary of Yangtze River, China

Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition. Among aquatic animals, body elemental ontogenetic changes may be particularly important in fish due to bone formation at larval-juvenile development stage. We investigated the stoichiometric characteristics and ontogenetic variation of carbon (C), nitrogen (N), phosphorous (P) and calcium (Ca) in the whole fish without gut of Lateolabrax macultus and Acanthogobius ommaturus from the Yangtze Estuary. Some differences were found in the whole-fish nutrient content across species as well as fish length and mass groups. Mean body content of L. macultus was 41.2% for C (34.9-44.9%), 11.8% for N (10.3-12.9%), and 3.3% for P (1.4-5.4%) and the molar ratio of C:N:P was 32:8:1. A. ommaturus had the following mean compositions: carbon, 43.4% (40.0-45.9%); nitrogen, 13.2% (11.7-14.1%); phosphorus, 2.9% (1.6-6.0%) and molar ratio of C:N:P was 38:10:1. The variation of C content in of L. macultus was minimum (0.05), followed by N (0.06), and the variation of P content was the highest (0.22). The variation of C content in A. ommaturus was minimum (0.03), followed by N (0.04), and the variation of P content was also the highest (0.27). Both species varied the least in C, moderate in N and the most in P. Comparing the two species, A. ommaturus was significantly higher for C, N, C:P, N:P and significantly lower for P and C:N than L. macultus. The positive correlation between C and N contents was significant (P < 0.01) for both species. In contrast, C and P concentrations showed little correlation (P > 0.05). The contents of C, N in L. macultus showed significant negative correlation with total length and wet mass, respectively, while C:N ratio showed significant positive correlation with them. As for A. ommaturus, the content of C and the ratio of C:N showed significant negative correlation with total length and wet mass, respectively. The two estuarine fishes in this study mainly consumed fish, shrimps and crabs, which could be the reason that the stoichiometry of L. macultus and A. ommaturus are higher than other freshwater fishes that have been reported previously. In both species, the content of calcium was highly correlated with the content of body P, which indicated that the change of the content of P is associated with bone formation in ontogeny. Fish shape, scale type, the ratio of head length/standard length and the degree of ossification of the internal skeleton and outer integument might have caused the results that L. macultus had higher contents of P and Ca than A. ommaturus.