June 13, 2011
Following flooding peaks in the Beni River, a massive upstream migration event involving juvenile pencil catfish (Trichomycterus barbouri) or chipi chipi is described for the first time. The annual migration begins in the floodplains of the Beni River, where enormous schools of juveniles form to travel upstream through the straits of the last foothills of the Andes into Andean foothill forest streams and rivers. Observations and local knowledge suggest a migration distance of at least 370 km over an average of 32 days in February and March with an average speed of 12 km/day. The migrating juveniles weigh less than 0.38 g and measure less than 33 mm in standard length. As such, considering body length and body weight to distance travelled ratios they are one have one of the greatest migration efforts of any freshwater fish. Local people harvest juveniles across the migration route, but especially in Rurrenabaque, where they are considered a seasonal dish. This scientific revelation highlights the Amazon as a place where natural phenomena are still being discovered, described and documented in an era when hydroelectric infrastructure threatens the ecology of many aquatic ecosystems.
The diet of Leptobotia elongata in the Yibin reach of the Yangtze River, China was investigated by stomach content analysis and by stable isotope analysis from muscle. The results of the two methods were agreement. Both stomach contents and isotope analysis indicated that L. elongatafed in spring mainly on plankton, shrimp and fish, and secondarily on benthic invertebrates and aquatic insect larvae. For the stomach content analysis, the diet composition showed significant differences among the size classes in relative weight of prey items, with L. elongata changing feeding habits at c.110 mm standard length. The smaller individuals fed on benthic invertebrates and aquatic insect larvae, whereas individuals >109 mm fed mainly on shrimp and fish. A similar shift to piscivory at c.110 mm standard length was found using the stable isotope mixing model to reveal dietary ontogeny by IsoSource software, and the trend in variation of the δ13C and δ15N was similar with increased body length, and the plankton is important prey item in all size classes. The δ13C and δ15N values in similar sized individuals showed significant seasonal differences (δ13C, ANOVA, F = 76.33, p < 0.001 and δ15N, ANOVA, F = 144.56, p < 0.001), indicating a temporal dietary and trophic level shift. L. elongata is an important commercial species, and the results of the study form part of a detailed investigation of feeding ecology of L. elongata that provides basic data for studying the food web of the upper Yangtze River.
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