Complex sentence: It has been suggested that very small larval fish are not able to feed on the spiny water flea itself because of the barbs the flea possesses, but it is readily consumed by several fish species once the fish are larger.
Split into simpler sentences: It has been suggested that very small larval fish are not able to feed on the spiny water flea itself because of the barbs the flea possesses. But it is readily consumed by several fish species once the fish are larger.