Aquatic Ecology and Water Environment Safety

CLC number: S965

Observation on the Embryonic and Larval Development of Leiocassis longirostris and Determination of Its Point of No Return under Starvation

长吻鮠胚胎、仔鱼发育观察及饥饿不可逆点的确定

¹ Fishes Conservation and Utilization in the Upper Reaches of the Yangtze River Key Laboratory of Sichuan Province, College of Fisheries, Neijiang Normal University, Neijiang 641100, Sichuan, China (内江师范学院　长江上游鱼类资源保护与利用四川省重点实验室，四川　内江　641100)
² Center for Conservation and Utilization of Rare and Endemic Fishes in Sichuan, Chengdu 611247, Sichuan, China (四川省珍稀特有鱼类保护与利用中心，四川　成都　611247)

^† Corresponding author. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 September 2025

Abstract

To investigate the embryonic and larval developmental characteristics of Leiocassis longirostris (L. longirostris) and determine the Point of No Return (PNR) of starved larvae, fertilized eggs were cultured in a recirculating glass aquarium maintained at a water temperature of (24.5 ± 0.5) ℃. Respectively, the chronological characteristics of embryonic and larval development were observed under a microscope, and starvation experiments were conducted on newly hatched larvae to study their morphological development, growth traits, and feeding capacity. The results indicated that the fertilized eggs of L. longirostris reached a diameter of (3.46 ± 0.16) mm after water absorption and swelling, and the embryonic incubation period was 68-70 h. Embryonic development was observed to progress through eight consecutive stages: fertilized egg, cleavage, blastula, gastrula, neurula, organogenesis, pre-hatching, and hatching. Subsequently, we observed that newly hatched larvae undergo three distinct developmental phases before initial feeding: the appearance of body pigments, the formation of the intestinal tract, and the first coiling of the intestinal tube. Thereafter, results from the larval starvation experiment indicated that L. longirostris larvae relied on endogenous nutrition within the first 4 days post-hatching (dph). Initial feeding occurred at 5 dph, with a feeding rate of (63.33 ± 2.89)%, marking the onset of the mixed nutritional stage. By 9 dph, the yolk sac was fully absorbed, and the larvae transitioned to exclusive exogenous nutrition. Moreover, the feeding rate remained at 100% from 8 to 11 dph, followed by a decline. The PNR was identified at 16 dph. Subsequently, complete starvation-induced mortality occurred between 16 and 17 dph. Thus, the optimal initial feeding time for L. longirostris larvae is recommended to be 5 dph. In summary, the findings of this study provide fundamental data on the early developmental stages of L. longirostris, which has significant practical implications for improving larval rearing efficiency in aquaculture.

摘要

为研究长吻鮠(Leiocassis longirostris)胚胎发育和仔鱼发育特点，确定仔鱼饥饿不可逆点(Point of No Return, PNR)，在水温(24.5 ± 0.5) ℃条件下孵化受精卵，用显微镜观察其胚胎和仔鱼发育时序特征，并开展初孵仔鱼的饥饿试验，研究长吻鮠仔鱼的形态发育、生长特征及摄食能力。结果表明，长吻鮠受精卵吸水膨胀后卵径为(3.46 ± 0.16) mm，68-70 h孵化出膜。胚胎历经受精卵期、卵裂期、囊胚期、原肠期、神经胚期、器官形成期、出膜前期和出膜期8个阶段。初孵仔鱼开口前，可观察出体色素出现、肠管建成和肠管弯曲期3个阶段。4日龄内长吻鮠仔鱼为内源性营养阶段，5日龄长吻鮠仔鱼初次开口，摄食率为(63.33 ± 2.89)%，开始混合性营养阶段，9日龄卵黄吸收完全，转为依赖外源性营养。8~11日龄摄食率为100%，之后开始减小，PNR为16日龄。16-17日龄仔鱼因饥饿全部死亡。因此，长吻鮠仔鱼最佳初次投喂时间在5日龄。本研究结果为长吻鮠早期发育阶段的探索提供了基础资料，对于高效苗种培育具有实践意义。