Research On Feeding Ecology Of Two Sciaenidae Species In The Southern Coastal Waters Of Zhejiang

As one of the important elements of fishery ecology research,the analysis of fish feeding habits can provide data support for the study of trophic relationships and population energy flow in marine food webs.The white croaker(Pennahia argentata)and the black croaker(Atrobucca nibe),belonging to Perciformes,is warm near-bottom fishes in the coastal waters.Widely distributed in the East China Sea,the Yellow Sea and other waters,they are common economic fishes in China and they also play an important role in the fishery industry of the southern coastal waters of Zhejiang.Previous data indicate that both species are benthic feeders and they are not only close in taxonomic status,but also have similar ecological habits such as distribution range,thermoregulation type,and spawning type,and thus potential feeding competition exists.However,prey overlap and feeding competition between the two species has rarely been reported.The application of high-throughput sequencing technology in the fish feeding analysis can compensate for the incomplete prey composition due to digestion and human identification errors caused by stomach contents analysis.There is still a lack of research using this high-precision identification method to analyze the feeding habits of Sciaenidae.In order to reasonably assess the feeding habits and diet overlap of these two Sciaenidae,287 stomach content samples of white croaker and 204 stomach content samples of black croaker,collected from bottom trawl surveys conducted in the southern coastal waters of Zhejiang in August and November 2020 and January 2021,were analyzed in this study.Statistical methods such as cluster analysis were used to investigate the changes in diet composition and feeding habits with body length.In addition,225 stomach content samples of black croaker collected in August 2022 were analyzed by stomach content analysis and high-throughput sequencing in batches(195for stomach content analysis and 30 for high-throughput sequencing)to comprehensively assess the diet composition of black croakers and to evaluate the feasibility of high-throughput sequencing in the diet analysis of Sciaenidae.Canonical Correspondence Analysis(CCA)was used to investigate the correlation between various environmental factors and the feeding habits of white croaker and black croaker.Finally,we compared the differences in the diet composition of the two fish species based on the data from the above studies on their feeding habits,calculated their nutrient ecological niche widths by the Shannon-Wiener index,and evaluated their diet overlap using the Pianka diet overlap coefficient.The main results are as follows:According to the Percentage Index of Relative Importance(IRI%),the diet of white croaker involved 48 species,which was dominated by Copepoda,mostly Calanus,and the diet of black croaker involved 43 species which were mainly fish and shrimp,with Benthosema pterotum as the dominant prey species.As body length increased,the main prey for both species shifted from small prey items such as zooplankton to large prey items such as fish and shrimp.The feeding intensity also changed with increasing body length,with white croaker decreasing gradually and black croaker decreasing and then increasing.Comparing the stomach contents analysis data of 2020 and 2022,the feeding preference of black croaker shifted significantly.The primary prey items shifted from fish to shrimp,while the dominant species was the Alpheus japonicus.This feeding shift was largely due to changes in the abundance of bait resources and their different spatial and temporal distributions.The high-throughput sequencing results of black croaker reflected similar prey items as the stomach contents analysis,with the dominant baits as shrimp and the dominant species as A.japonicus.Comparing the diet results of both approaches,high-throughput sequencing provided more numerous and more accurate data,and also allowed for the identification of new prey items that were easily digestible.However,the number of identical prey between the two approaches is small and there are multiple factors that affect the accuracy of high-throughput sequencing results.Comparing the results of stomach contents analysis and high-throughput sequencing,we found that the latter is feasible as a high-precision semi-quantitative analysis.However,the high-throughput sequencing must be combined with morphological methods to obtain more complete feeding data.The CCA results indicated that dissolved oxygen,salinity,temperature,and body length were significantly correlated with the feeding habits of Sciaenidae.Among them,the food composition of both white and black croaker in 2020 was influenced by salinity.In addition,body length also influenced the feeding of large prey items by white croaker.And dissolved oxygen was the main factor influencing the feeding habits of black croaker in 2022.Large numbers of phytoplankton gathered in the high DO areas.Ostracoda and mysida were attracted to feed there and black croaker had more possibilities and opportunities to hunt them.It revealed the interaction of organisms at each trophic level in the marine ecosystem.The width of trophic niche of the two species was significantly different.The width of trophic niche of black croaker(3.06)was higher than that of white croaker(1.82),indicating that black croaker was more capable of utilizing prey resources and had a wider range of utilization.White croaker consumed more prey items than black croaker.However,the percentage of number of Copepoda in the prey items of white croaker reached 65.57%,which was much larger than that of other items,indicating the high specialization of their diet.The overall diet overlap coefficient between them was 0.22,indicating that they did not have a high level of feeding overlap in general.However,there was a large diet overlap in some body length groups,which indicated the possibility of food competition between them at some growth stages.Few amounts of white croaker were identified from the stomach contents of black croaker by both stomach contents analysis and high-throughput sequencing,suggesting a predator-prey relationship between both of them.It might also be one of the reasons for the low degree of diet overlap between both Sciaenidae.In general,the prey items of white croaker and black croaker differed considerably in the southern coastal waters of Zhejiang,and the degree of diet overlap was not too high,which contributed to both Sciaenidae becoming economically important.