Variation in the structure of the ichthyoplankton community in the lower Paraíba do Sul River

ABSTRACT The Paraíba do Sul River is affected by extensive water collection for supply, organic and industrial pollution, and dams. Nonetheless, the ichthyofauna maintains biodiversity and sustains artisanal fisheries. This study analyzes the composition, abundance and distribution of fish larvae, an important approach to determine the reproductive period and spawning sites. The sampling occurred from August 2011 through February 2013 in five sites at a transect between the banks on the lower reach of the Paraíba do Sul River. A total of 5,412 larvae belonging to 20 taxa was captured. The predominant order was Characiformes. Larvae of Prochilodus spp. and Leporinus spp. were the most abundant; larvae of Brycon insignis, an endangered species, were present. Fewer larvae were collected in the second reproductive cycle during a severe drought. The absence of eggs indicates that the study area is not used for spawning, and highlights the need for studies in the main channel and in the tributaries of the Paraíba do Sul River. Fish larvae need to have access to the marginal lagoons along the lower stretch of the river, an area which is the object of disputes between fishermen and farmers.

摘要 南帕拉伊巴河（Paraíba do Sul River）受大规模供水取水、有机污染与工业污染以及水坝工程的多重影响。尽管如此，该流域的鱼类区系仍维持着生物多样性，并支撑着当地的传统手工渔业。本研究针对鱼类仔鱼的组成、丰度与分布格局展开分析，这是探明鱼类繁殖期与产卵场的重要研究途径。采样工作于2011年8月至2013年2月间开展，在南帕拉伊巴河下游河段的沿岸样带内设置5个采样点。本次采样共采集到隶属于20个分类单元的鱼类仔鱼5412尾，优势类群为脂鲤目（Characiformes）。其中原唇齿脂鲤属（Prochilodus spp.）与兔脂鲤属（Leporinus spp.）的仔鱼丰度最高；濒危物种亮颊脂鲤（Brycon insignis）的仔鱼亦有采集到。在遭遇严重干旱的第二个繁殖周期中，采集到的仔鱼数量大幅减少。未采集到鱼卵的结果表明，本研究区域并非鱼类产卵场，同时凸显了针对南帕拉伊巴河主河道及支流开展相关研究的必要性。鱼类仔鱼需要利用河流下游沿岸的潟湖生境，而该区域正是渔民与农户间的争议地带。