LIU, C*; GIBB, A.C.; Northern Arizona University; Northern Arizona University: Embryonic development and escape behavior in Oncorhynchus mykiss

Rainbow trout, Oncorhynchus mykiss, embryos hatch from the egg with a large yolk mass and in an advanced state of morphological development. Our previous research has shown that O. mykiss embryos are very coordinated immediately after hatching and produce highly effective escape responses relative to other fish species. In this study, we examine the ability of embryonic O. mykiss to produce escape responses early in development, before hatching. O. mykiss embryos were acquired from a commercial vendor and maintained in a chilled aquarium at 13 degrees Celsius. After manually removing the embryos from their egg sacs, we provided a negative tactile stimulus and recorded the resulting escape behavior using high-speed digital imaging. We recorded escape behaviors from embryonic Oncorhynchus mykiss for the last week before hatching and recorded at least four behaviors from an average of five fish on each day. We subsequently analyzed these sequences by placing them into three behavioral categories: the embryos either �wiggled�, did a �quasi-C-start�, or a �true C-start.� The percentage of each type of response changed each day as the embryos approached the hatch date. In the beginning, most of the embryos simply wiggled, whereas towards the hatch date, each fish was consistently able to perform a true C-start. These results suggest that the normal escape behavior, the C-start, develops prior to hatching for this species. O. mykiss, typically live and reproduce in swift-flowing streams, so it is possible that the escape response develops before hatching to enable fish to survive if water turbulence or predator contact triggers and premature hatching.