Morphological observation of larval, juvenile and young humphead wrasse (Cheilinus undulatus)

To elucidate the morphological characteristics and growth pattern during post-embryonic development of humphead wrasse (Cheilinus undulatus) and to provide a theoretical basis for germplasm conservation and artificial seedling rearing, we carried out systematic morphological observation and growth fitting analysis on larvae, juveniles, and young fish at 0–97 days post hatching (dph) under a rearing water temperature of 27.8–36.0 ℃. The results show that the post-embryonic development of C. undulatus divides into three stages. Larval stage (0–20 dph): newly hatched larvae had a total length of (1.94±0.05) mm, with an elliptical yolk sac and a terminal oil globule. First feeding occurred at 3 dph, with a mouth gape of approximately 130 μm. Anal, dorsal, and caudal fin buds appeared sequentially between 11 and 13 dph. The larvae were transparent and swam by twisting or diving movements. Juvenile stage (21–76 dph): at 21 dph, the fish entered the juvenile stage, with a total length of 6.96±0.13 mm. All fins were mostly formed, and scales began to cover the abdomen. By 27 dph, the head and most of the trunk were covered with scales, and gray-brown spots appeared on the body surface. At 71 dph, juveniles reached a total length of (26.86±1.06) mm, with a conical head and gray-brown spots covering the trunk scales. Young fish stage (77 dph): at 77 dph, the fish entered the young fish stage, with a total length of (27.38±1.76) mm. The body was fully covered with scales, appearing light yellow, with gray-brown pigmentation deepening to dark brown between scale rows. Three short transverse black bars appeared behind the eyes, representing the typical morphological characteristics of adults. Growth fitting indicates that total length, preanal length, and body height each exhibited a cubic polynomial relationship with age (r²>0.97), showed a "slow-fast-slow" growth trend, and displayed allometric growth during the juvenile stage. However, their developmental rate was significantly slower than that of most common tropical marine fish species.