NORMAL AND ABNORMAL JAW DEVELOPMENT OF THE YOLK-SAC LARVA OF ATLANTIC HALIBUT HIPPOGLOSSUS-HIPPOGLOSSUS

Normal and abnormal jaw development was studied in laboratory-reared halibut larvae by light and electron microscopy. Abrasion of the epidermis of the tail and head with invasion by bacteria and other foreign organisms was common, especially in larvae grown in wells. Mouth and jaw development was often delayed in larvae with eroded tails. Perforation of the oral membrane in larvae without lesions was not seen until 29 d at 5 degrees C (145 degree-days); younger larvae with mouths possessed lesions on the head, which appeared to be associated with premature breakdown of the oral membrane. Many larvae had gaping jaws, a condition which causes major problems in rearing, since these larvae cannot close their jaws to feed. We found that the jaws of these larvae were not disarticulated, but the anterior parts of the ethmoid and Meckel's cartilages were bent apart. This condition appeared to be associated with abrasion of the head, and invasion by foreign organisms.