A macroscopic classification of the embryonic development of the one-sided livebearer Jenynsia multidentata (Teleostei: Anablepidae)

ABSTRACT This study proposes eight stages according to the main discernible changes recorded throughout the embryonic development of Jenynsia multidentata. The development of morphological embryo structures, pigmentation, and changes in tissues connecting mother and embryo were included in the stage characterization. From the fertilized egg (Stage 1), an embryo reaches the intermediary stages when presenting yolk syncytial layer (Stage 2), initial pigmentation of the outer layers of the retina and dorsal region of the head (Stage 3), and the sprouting of the caudal (Stage 4), dorsal and anal fins (Stage 5). During the later stages, the ovarian folds enter the gills, and the body pigmentation becomes more intense (Stage 6), the body becomes elongated (Stage 7), and there is a greater intensity in body pigmentation and increased muscle mass (Stage 8). The dry weight of the batches varied between 0.6 ± 0.3 mg (Stage 3) to 54.6 ± 19.7 mg (Stage 8), but the dry weight of the maternal-embryonic connecting tissues remained almost constant. After controlling the effect of those reproductive tissues, the gain in dry weight of the batches throughout development increased exponentially from Stage 6, reflecting the increase in size and weight of the embryos due to matrotrophy.

摘要：本研究依据多齿詹氏鱼（Jenynsia multidentata）胚胎发育全程中可识别的主要形态变化，将其胚胎发育划分为8个阶段。本次阶段划分与特征表征工作涵盖了胚胎形态结构发育、色素沉着动态变化，以及母本与胚胎间连接组织的演化特征。
发育起始于受精卵（阶段1），后续胚胎依次经历形成卵黄合胞体层（yolk syncytial layer）的阶段2、视网膜外层与头部背侧区域初次出现色素沉着的阶段3、尾鳍萌出的阶段4，以及背鳍与臀鳍萌出的阶段5。
进入发育后期后，卵巢褶侵入鳃腔，躯体色素沉着进一步加深（阶段6）；躯体逐渐伸长（阶段7）；至阶段8时，躯体色素沉着程度进一步提升，肌肉量显著增加。
各组胚胎样本的干重范围为0.6±0.3 mg（阶段3）至54.6±19.7 mg（阶段8），但母本-胚胎连接组织的干重基本保持恒定。
在控制此类生殖组织的影响效应后，各组胚胎在发育全程的干重增益自阶段6起呈指数级增长，这一现象反映了胚胎因亲体营养（matrotrophy）作用而导致的个体尺寸与重量的提升。