By analyzing 1664 stomach samples (575 white croaker Argyrosomus argentatus and 1089 small yellow croaker Pseudosciaena polyactis) collected nearby Changjiang estuary in summer and autumn 2006,we studied the feeding habits of these two species. Multivariate statistical technique was used to analyse data on the habitat,seasonal and ontogenetic variations in diet. In this study,percentage index of relative importance (%IRI) and the majority rule,by which over 60% of prey in the diet composition was defined as the major prey,were applied to determine feeding patterns. One-way Analysis of Similarities (ANOSIM) was performed to test the difference between species and seasons among the dietary compositions of the two sciaenid fishes in the waters around Changjiang estuary. Similarity Percentages (SIMPER) were used to determine which dietary categories typified particular groups and were most responsible for any dissimilarity between groups. Seasonal variations in the mean stomach fullness index and percentage of empty stomachs were tested by Kruskal-Wallis and χ2-tests. Ontogenetic variation in diets was examined by grouping white croaker and small yellow croaker length into six and nine size classes,respectively,based on cluster analysis by running the PRIMER version 5.0 package. Cluster analysis employing the 60% Bray-Curtis Similarity Index was performed to determine ontogenetic variations in dietary composition.Results showed that the white croaker fed on 35 species,and the small yellow croaker fed on 41 species. Crustaceans were the most important prey and accounted for over 83% of the total food of both species,thereinto decapoda accounted for over 50% of total diet. Dietary compositions differed significantly between the two sciaenid species. Japanese snapping shrimp Alpheus japonicus and mantis shrimp Oratosquilla oratoria were more important in the diets of the white croaker,while lesser glass shrimp Leptochela gracilis and Northern maoxia shrimp Acetes chinensis were more important in the diets of the small yellow croaker. Therefore,feeding on different dominant prey species between the two sciaenid fishes reduces the likelihood of serious dietary competition. Compared with the 1980 s,the proportion of fish in their diets had declined.Dietary compositions of the white croaker and the small yellow croaker varied with habitat. Compared with the data from the Yellow Sea and East China Sea obtained in recent years,the diet of the white croaker was similar (benthivorous) in different waters. The diet of small yellow croaker showed some differences;feeding habits of small yellow croaker were omnivorous in the Yellow Sea and East China Sea,and zooplankton was the dominant prey,in Changjiang estuary and it fed mainly on decapoda. The dominant prey species of small yellow croaker in the central part of Yellow Sea was Pacific krill Euphausia pacifica,lesser glass shrimp and rednose anchovy Thryssa kammalensis . This study found that the dominant prey species of small yellow croaker in the waters of Changjiang estuary were Northern maoxia shrimp,leaser glass shrimp and skinnycheek lanternfish Myctophum pterotum.Feeding intensity of the white croaker and the small yellow croaker in autumn was higher than those in summer. The seasonal variations in feeding intensity may be related to two interacting factors: one is variation in availability of food resources in different seasons;the other is energy storage required for physiological activities,such as growth,reproduction and over-wintering. Seasonal variations in diet compositions were different between the two sciaenid fishes. The diet compositions of the white croaker in autumn and summer were similar;all were benthivorous,decapoda and Stomatopoda were the dominant prey. The dietary compositions of the small yellow croaker in autumn and summer were different. The feeding habit was benthivorous in summer,and mainly involved decapoda;while it was a zooplanktivous fish and fed mainly on acetes in autumn.The results indicated that the feeding habit of the white croaker near the Changjiang estuary (ranging in length from 31 mm to 197 mm),had no obvious ontogenetic variation. But ontogenetic differences in feeding habit were found in the small yellow croaker (length from 62 mm to 185 mm). Fish shorter than 109 mm were benthivorous and fed mainly on decapoda,while prey items increased for fish longer than 109 mm. These were omnivorous fish,and fed on other fish,decapoda and zooplankton. Comparison with the small yellow croaker in the central part of Yellow Sea,showed that the feeding habit changed from zooplanktivorous to omnivorous at 109 mm. 109 mm is a key critical length,at which the feeding habit of the small yellow croaker changes. This ontogenetic change in feeding behaviour is probably an inherent trait,which does not change with habitat.
NETL
NSTL
维普
万方数据
