Ovarian development and spawning of Macrobrachium amazonicum (Crustacea, Decapoda)

ABSTRACT Macrobrachium amazonicum (Heller, 1862) is the most important species for aquaculture native to South America. This study evaluates the phenotypic plasticity of females of Macrobrachium amazonicum with respect to the gonadal development, and determines the spawning type. Our study consisted of macro and microscopic analysis of the reproductive tract. Ovaries exhibited the following reproductive cells in developmental sequence: oogonia (OO) - mean diameter and standard deviation of 25.4 ± 6.5 μm; previtellogenic oocyte (PVO) - 61.7 ± 10.7 μm, vitellogenic oocyte (VO) - 113.9 ± 24.5 μm; and mature oocyte (MO) - 308.7 ± 56.3 μm. Ovaries increased in volume due to vitellogenesis and changing of basophilic to acidophilic composition. Follicular cells, atresic oocytes and postovulatory follicles were also analyzed. By combining macro and microscopic analysis, the ovaries of M. amazonicum were classified into six stages: Immature, In maturation, Mature, Spawned in maturation, Spawned and Resting. The ovarian development of M. amazonicum followed a standard pattern even among different populations. Considering our results and the evidence in literature, we conclude that spawning for this species is parceled or multiple, that is, synchronous in more than two groups (clutches of oocytes). Such observations provide basis for further studies addressing sustainable management strategies for species conservation and contribute to elucidate the biology of their specimens.

摘要 亚马逊沼虾（Macrobrachium amazonicum，Heller, 1862）是南美本土最重要的水产养殖物种。本研究针对亚马逊沼虾雌性个体的性腺发育情况评估其表型可塑性，并明确其产卵类型。本研究采用生殖系统宏观与微观分析的方法开展。卵巢内的生殖细胞按发育顺序依次为：卵原细胞（oogonia，缩写OO），平均直径及标准差为25.4±6.5 μm；卵黄发生前卵母细胞（previtellogenic oocyte，缩写PVO），直径为61.7±10.7 μm；卵黄发生期卵母细胞（vitellogenic oocyte，缩写VO），直径为113.9±24.5 μm；以及成熟卵母细胞（mature oocyte，缩写MO），直径为308.7±56.3 μm。卵巢体积随卵黄发生过程增大，且其组织成分由嗜碱性转变为嗜酸性。本研究同时对滤泡细胞、闭锁卵母细胞及排卵后滤泡进行了分析。结合宏观与微观分析结果，亚马逊沼虾的卵巢可划分为六个发育阶段：未成熟阶段、成熟中阶段、成熟阶段、成熟期产卵阶段、已产卵阶段及休止阶段。即便来自不同种群，亚马逊沼虾的卵巢发育仍遵循统一模式。综合本研究结果与现有文献证据，本研究判定该物种的产卵方式为分批产卵或多批次产卵，即存在两组及以上卵母细胞产卵群的同步发育。上述研究结果可为该物种保护的可持续管理策略相关后续研究提供依据，同时有助于阐明该物种的生物学特性。