First observations and early life-history aspects of lake rearing galaxiid larvae in the lower Waikato River Basin, New Zealand

Larval behaviour for many of New Zealand’s diadromous freshwater fish is inadequately described. Diadromy for many amphidromous species is not obligatory however, and where conditions are suitable, freshwater larval rearing may be facilitated. Where this occurs in lakes, opportunities to document the composition and conditions supporting larval rearing exist. Boat trawling was undertaken across nine lowland lakes in the Lower Waikato over four consecutive winters with a focus on larval galaxiids. Galaxiid larvae were captured in surface water habitats in all but one lake, with banded kōkopu (<i>Galaxias fasciatus</i>) and giant kōkopu (<i>Galaxias argenteus</i>) the most common species detected. One lake, Lake Waahi, consistently resulted in the most galaxiid captures for effort expended. Analyses of larvae from this and other lakes indicated that two sizes predominated in catches and that larger, older larvae were predominantly <i>G. fasciatus</i> while smaller, younger larvae were predominantly <i>G. argenteus</i>. Stomach contents indicated that two non-native zooplankton species predominated in the diet of larvae, the Holarctic daphnia, <i>Daphnia galeata</i>, and the Australian calanoid copepod <i>Boeckella symmetrica</i>. This study provides new information regarding the timing, movement and predicted recruitment of native fish species in this river basin that has important implications for lake and river management.

新西兰众多溯河洄游（diadromous）淡水鱼类的幼体行为尚未得到充分描述。不过，许多两栖洄游（amphidromous）物种的洄游习性并非强制性的，当环境条件适宜时，可在淡水环境中完成幼体培育。若在湖泊中出现此类淡水幼体培育现象，则有机会记录支持幼体培育的群落组成与环境条件。
研究团队在连续四个冬季期间，于怀卡托河下游的九座低地湖泊中开展船拖网采样，重点关注南乳鱼科（Galaxiidae）鱼类幼体。除一座湖泊外，其余所有湖泊的表层水体生境中均捕获到南乳鱼幼体，其中带纹南乳鱼（*Galaxias fasciatus*）与巨南乳鱼（*Galaxias argenteus*）为检出的优势物种。
怀希湖（Lake Waahi）在单位采样投入下的南乳鱼捕获量始终位居榜首。对该湖及其他湖泊的幼体样本进行分析后发现，捕获的幼体主要分为两种体型：体型更大、发育更成熟的幼体以带纹南乳鱼为主，而体型更小、发育阶段更年轻的幼体则以巨南乳鱼为主。
胃容物分析结果显示，幼体的食谱以两种外来浮游动物为绝对优势类群：全北区分布的隆线溞（*Daphnia galeata*），以及澳大利亚原产的对称博克哲水蚤（*Boeckella symmetrica*）。
本研究为该流域内本土鱼类的活动节律、迁移模式及潜在种群补充情况提供了全新数据，其研究结果对湖泊与河流的管理工作具有重要参考价值。