Feeding Habits Of Acanthogobius Ommaturus In The Yangtze Estuary And The Effects Of Turbidity On Foraging

Acanthogobius ommaturus is the main prey items of juvenile Acipenser sinensis, and it plays an important role in the Yangtze Estuary ecosystem, but it faces fishing pressure is also growing. In recent years, large-scale water conservancy construction upper Yangtze River has been made the Yangtze Estuary in turbulent times, and it is bound to affect the distribution of fish resources. Feeding is an important activity to maintain its survival, growth and reproduction. Through field investigation and laboratory simulation method, we investigated feeding habits and feeding behavior of Acanthogobius ommaturus, to provide a scientific basis for the protection of this fishery resources and sustainable development of ecosystems. It also provides a reference for the construction of food web in the Yangtze Estuary.1. Feeding habits of Acanthogobius ommaturus in the Yangtze EstuaryThe Yangtze Estuary is the largest estuary of the Pacific West Bank, it is an important spawning grounds, feeding grounds, wintering grounds and migration routes of fish. Acanthogobius ommaturus has some economic value, but few scholars research on it. Feeding study is not only the main research of fish biology and ecology, but also an important basis for understanding fish community and the entire ecosystem structure and function. So far, domestic and foreign scholars have conducted some researches on the feeding of Acanthogobius ommaturus, but the study of Acanthogobius ommaturus in the Yangtze Estuary have not been done. The feeding habits of Acanthogobius ommaturus was investigated for 459 individuals collected bimonthly from the Yangtze Estuary(June 2014 to May 2015),and their stomach contents were analyzed. The results indicated that the prey items of the Acanthogobius ommaturus included 12 groups or 37 prey species with decapoda dominating. Prey groups also included mysidacea, fishes and crabs. The advantage prey species are Exopalaemon carinicauda and Mysidacea. Prey items were similar with other scholars’ research results in Jiaozhou Bay, Bohai sea, Laizhou Bay and Huanghe Delta. But the advantage prey species are not the same. Thus, the habitat of prey items determines the dietary composition of Acanthogobius ommaturus. The dietary composition of the prey consumed had obvious seasonal variations. While decapoda was an important prey group across all seasons, mysidacea and crabs were predominant in spring, fish in summer, while mysidacea were eaten mostly in winter. Seasonal variation of dietary composition is closely related with fish life cycle and the seaso nal changes of prey items. The dietary composition also had obvious ontogenetic variations: <70 mm SL(standard length) consumed juvenile fishes, mysidacea and euphausiacea, 70~189 mm SL consumed shrimps and fishes, while >189 mm SL mainly consumed fishes. The species and the size of prey items showed extremely significant difference in body length. Cluster analysis with seasons employing Euclidean distance index revealed two diet groups : one group in autumn, the other group in spring, summer and winter. C luster analysis with ontogenetic revealed two diet groups :one group <70 mm, the other group ≥ 70 mm. The feeding intensity had obvious seasonal variations and ontogenetic variations: Kruskal-Wallis nonparametric rank test and contingency table test revealed that mean stomach fullness index of Acanthogobius ommaturus varied seasonally(P<0.01), percentage of empty stomachs was not significantly different among the season(P>0.05), mean stomach fullness index and percentage of empty stomachs varied with ontogenetic(P<0.01). Feeding intensity of Acanthogobius ommaturus in winter was lower than that in autumn may be related to the reduce of the number of prey and the temperature. While higher than spring, summer may be related to the larger SL. A strong positive relationship was found between the body lengths of prey and Acanthogobius ommaturus(rs=0.263,P<0.01). Namely, with the growth of Acanthogobius ommaturus, its mouthparts gradually improved, and the predation gradually increased. Moreover, the mean prey weight and mean prey number increased with the increasing of body length, this is consistent with “optimal foraging theory”.2.Diet feeding rhythm of Acanthogobius ommaturus and the effects of turbidity on foragingWe investigated the d iet feeding rhythm of Acanthogobius ommaturus and the effects of turbidity on foraging. The food composition of Acanthogobius ommaturus was determined at turbidity of 0, 50, 100, 150, 200 NTU and 8:00, 12:00, 16:00, 20:00, 00:00, 4:00.The results showed that turbidity had no significant effect on diet food composition(P>0.05). In a day and night, there is significant difference in food composition, it extreme high at 8:00-12:00. It appeared that Acanthogobius ommaturus was identical with the daytime feeding. We investigate the d iet feeding rhythm of Acanthogobius ommaturus in different turbidity conditions, it turns out that turbidity does not affect the diet feeding rhythm in the range of 200 NTU.3. Effects of turbidity on the reactive distance, search time of Acanthogobius ommaturusWe investigated the effects of turbidity on the foraging behavior of Acanthogobius ommaturus on shrimp prey in the laboratory. The influence of turbidity on foraging was examined by measuring reactive distances and search times over turbidity levels ranging from 0 to 200 N TU. It turned out that turbidity had a significant effect on reactive distance(P<0.05). The reaction distance is longer at 0 and 50 N TU than the other three groups. When turbidity greater than 100 NTU, as turbidity increases, the reactive distance was significantly reduced, but the reaction distance was no significant difference in 100, 150 and 200 NTU. And, turbidity also had a significant effect on search time(P<0.05). Despite the search time had great changes, it tends to increase with the turbidity becomes longer. This study have laid the foundation for the further research about the role of a single sensory organ in the feeding behavior.