Development of Eggs, Larvae and Juvenile of the Korean Bullhead, Pseudobagrus fulvidraco (Richardson) reared in the laboratory

동자개의 형태발달과 성장특성

The early developmental stages, growth and morphological changes of the Korean bullhead, Pseudobagrus fulvidraco, were studied from a series of reared specimens. Details of the early developmental stages are illustrated with special reference to morphological transformations. Egg and sperm of Korean bullhead were obtained from mature adults under hormonal treatment, fertilized artificially, and incubated in the aquarium. The incubation period of fertilized eggs was 55 to 66 hours at a temperature of 24.9${\pm}$0.34$^{\circ}$. Larvae were fed successively with Artemia salina and Daphnia magna for 2 to 15 days and artificial food after 20 days. Fertilized eggs were adhesive and spherical with a diameter of 2.04mm(n = 100). The mean total length of newly hatched larvae was about 4.92${\pm}$0.33 mm. Mouth opening occurred on one-day-old yolk-sac larvae, and initial feeding was observed on the third day after hatching. The morphological transitions from larvae to juvenile and juvenile to young stages occurred when the fish reached about 17 mm in total length (about 13days after hatching) and about 32 mm in total length (about 30 days after hatching), respectively. Many changes in proportion of body parts to total length were observed at about 7~8 mm and 30~32 mm, corresponding to the transformations from larvae to juvenile and from juvenile to young, respectively. In comparing relative growth of each body part against total length, those characteristics related to head parts showed positive growth in the pre-larval stages, while those concerning mobile abilities showed positive growth in the post-larval stage.

사육 조건하에서 동자개 Pseudobagrus fulvidraco의 발육에 따른 형태 변화 및 상대성장에 대해 검토하여 발육단계를 구분한 결과를 요약하면 다음과 같다. 1. 수정난은 난경 2.04${\pm}$0.07 mm (n = 100)의 비교적 큰 구형의 분리되는 침성부착난으로서 수조의 바닥 및 기질에 강하게 부착한다. 2. 부화자어는 전장 약 4.92${\pm}$0.33 mm로, 부화 후 1일에 입이 열리고, 부화 2일후에는 항문이 열리고, 부화 후 3일에 섭이를 시작하여 후기자어기에, 부화 후 30일경에 전장 약 32 mm에 유어기에 이른다. 3. 전장에 대한 각 부위의 상대성장에 굴곡점은 전장 7~8 mm, 17~32 mm, 32 mm 전후에 집중적으로 나타났다. 4. 외부형태의 변화 및 상대성장의 굴곡점이 나타나는 어체 크기 등을 종합적으로 고려하여 자어기에서 유어기까지의 발육단계를 구분하면, 자어기는 전장 17 mm 이하, 치어기는 17~32 mm, 유어기는 32 mm 이상으로 사료된다. 상대성장의 측정결과 전기자어기에는 머리부분에 관련된 형질, 후기자어기 이후에는 운동능력에 관련된 형질의 우성장이 뚜렷하였다.