GIBB, A. C.*; LIU, C.; SWANSON, B. O.; Northern Arizona University; Northern Arizona University; Pacific University: Pre-hatching escape behavior in the rainbow trout

Teleost fishes employ diverse developmental strategies that have direct consequences on the ability to perform certain behaviors. Danio rerio, zebrafish, have indirect development, where embryos hatch within four days of spawning, and skeletal elements of the cranium and fins are unformed. In contrast, Oncorhynchus mykiss, rainbow trout, have intermediate development, where embryos hatch 35 days after spawning, and skeletal elements of the cranium and fins are well formed. After hatching, both species produce an effective escape response that moves the fish�s center of mass away from potential predators. Previous research on decapsulated (i.e., the chorion is artificially removed) zebra fish embryos demonstrated that a coordinated escape response behavior appears at approximately the same time as hatching. Given the advanced state of morphological development of the rainbow trout, we predicted that an effective escape response would appear well before hatching in this species. To test this prediction, we decapsulated rainbow trout embryos from as early as five days before hatching and solicited escape responses. Surprisingly, the pattern we observed for rainbow trout was similar to that seen in zebrafish: uncoordinated movements occurred in the days before hatching, and an effective escape response only appeared within the 24 hours before hatching. Thus, the development of this particular behavior is uncoupled from development of the skeletal system. Given the advanced state of development of rainbow trout at hatching, it is likely that the elements of the neural pathway that enable the escape response (e.g., sensory, Mauthner and motor neurons) develop well before hatching. However, this pathway only produces a coordinated and effective escape behavior at hatching, when it is useful to the organism.