Developmental characteristics and point of no return of larval and juvenile Diptychus maculatus Steindachner under starvation

Mastering the basic biological characteristics and relevant data of Diptychus maculatus Steindachner, and facilitating the restoration and sustainable development of its natural resources, constitute the essential foundation and prerequisite for carrying out conservation research on rare and endangered species in the Ili River Basin. Under water temperatures of 12.2–13.4 ℃, we continuously observed the morphological development of larvae and juvenile fish, and recorded the growth indicators and characteristics. Ecological experiments were conducted to induce starvation in newly hatched larvae, examining changes in morphology, growth, survival rate, and the point of no return (PNR) under starvation stress. Based on developmental characteristics, the early life stages were divided into three periods: the early larval stage (0−14 days post hatching, dph), the late larval stage (15−254 dph), and the juvenile stage (255−592 dph). Newly hatched larvae measured (10.30±0.05) mm in total length, with a yolk sac volume of (12.96±0.51) mm³. Larvae first fed at 11 dph, and the yolk sac was completely absorbed by 14 dph. Scales appeared at 255 dph, marking the transition to the juvenile stage. By 592 dph, the body was fully covered with scales, and the morphology resembled that of adult fish, signifying the end of the juvenile stage and the transition to the young fish stage. In the control group, the yolk sac was completely absorbed by 14 dph, while in the starvation group, absorption was completed by 16 dph. The mixed feeding period lasted 3–5 days, during which larvae were highly vulnerable to starvation stress. First feeding occurred at 11 dph, with a feeding rate of only 5%; the feeding rate reached 100% by 16 dph. The PNR occurred at 23 dph. The early larval stage of D. maculatus lasted 14 d, the late larval stage 240 d, and the juvenile stage 338 d. Post-larvae entered the young fish stage after 592 dph. These data provide a reference for studies on the early development of D. maculatus. Initial feeding can commence with small quantities at 11 dph, with 13 dph being optimal. However, feeding should commence no later than 19 dph.