Effect of body size heterogeneity on the aggressive behavior of larvae of matrinxã, Brycon amazonicus (Characiformes, Bryconidae)

ABSTRACT Brycon amazonicus is a native Amazonian fish that is important for aquaculture in South America. Larval mortality is high in this species in intensive breeding systems due to aggressiveness among larvae. The present study investigated experimentally the effects of body size heterogeneity on the aggressive behavior and survival of B. amazonicus during the early stages of larval development. Two treatments (larvae groups with homogeneous and heterogeneous body size) were evaluated throughout early larval stages tested at six time points: 12, 24, 36, 48, 60 and 72 hours after hatching (HAH). Two experiments quantified, respectively, aggressive interactions and mortality rates among larvae at each time point. The frequency of aggressive interactions exhibited by the less aggressive larvae in each replicate was higher in the homogeneous size treatment. Aggressiveness was higher at 12 HAH, decreasing thereafter, and increasing again at 72 HAH. The mortality rate significantly increased with the larval stage, and was higher in the homogeneous than in the heterogeneous sized groups. Our results showed that aggressiveness in B. amazonicus larvae is affected by size variability and larval development stage. This knowledge about larval behavior is important to develop measures to improve larval health and survival in intensive production systems for this species.

摘要：亚马逊河Brycon鱼（Brycon amazonicus）是亚马逊流域原生鱼类，为南美洲水产养殖的重要物种。该物种在集约化繁育系统中，因幼体间的攻击行为导致幼体死亡率居高不下。本研究通过实验探究了体型异质性对亚马逊河Brycon鱼幼体发育早期阶段攻击行为与存活率的影响。本研究设置两组处理：体型均一化幼虫组与体型异质化幼虫组，并在幼体发育早期的6个时间点（孵化后12、24、36、48、60和72小时，HAH）开展评估。两项实验分别量化了各时间点下幼虫间的攻击互作与死亡率。结果显示，在体型均一化处理组中，各重复组内低攻击性幼虫的攻击互作频率更高。攻击行为强度在孵化后12小时达到峰值，随后逐渐降低，并在孵化后72小时再次升高。死亡率随幼体发育阶段显著上升，且体型均一化组的死亡率显著高于体型异质化组。本研究结果表明，亚马逊河Brycon鱼幼体的攻击行为受体型变异与幼体发育阶段共同影响。上述关于幼体行为的研究结论，可为该物种集约化养殖体系中制定提升幼体健康与存活率的相关措施提供理论支撑。