Too small to catch prey, larval fish starve

WEST PALM BEACH, FLORIDA—To see a fish snag a snack can be quite impressive. Many species sneak up on unsuspecting prey and suck them in without getting very close to the tasty morsel. But suction feeding doesn't come easily when fish first hatch. In the wild, 99% of fish larvae die. Even when the newborns are protected from predators and harsh living conditions and given access to plenty of food, 70% still succumb. The reason, researchers in Israel showed in mid-2014, is that very young fish are terrible at sucking in their food (see video above), particularly in the first day after hatching. Now, using high-speed video and analyzing hundreds of prey-catching attempts, that team has determined that larval fish fail to take in prey fast enough to swallow it. Also, water currents set up inside the mouth, sometimes pushing the prey back out, they reported here today at the annual meeting of the Society for Integrative and Comparative Biology. For those little fish, the water seems thick and hard to push around. In just a few days, however, the fish that do make it grow big enough to move water effectively into their mouths. So why don't fish evolve to lay bigger eggs and hatch bigger larvae more able to swallow prey? The researchers say computer modeling suggests that there is a size trade-off: Bigger eggs might allow bigger larvae that are more likely to survive, but not the easy diffusion of oxygen the developing embryos need to survive.

(Main video credit: Miri Zilka; linked video credit: Peter Wainwright, University of California, Davis)