Fish enemies are usually transferred to the aquarium by the introduction of new aquatic plants that are obtained from outside pools. To avoid fish enemies—AVOID USING PLANTS AND SAND THAT ARE OBTAINED FROM OUTSIDE POOLS OR PONDS. If you are suspicious of source rinse for a minute or two through a strong solution of salt water. This should kill all insects and not injure plants. Examine plants carefully for eggs. Fig. 6 shows larvae of Giant Beetle (Water Tiger). Fig. 7, larvae of Dragon Fly. Both attack fairly large fish and devour small ones in quantities.

HYDRA—a polyp, fastens itself to plants or glass. It has a variety of shapes and is hard to distinguish particularly on plants. It attacks and quickly drugs fish by injecting a poison. Hydra can be killed by removing all fish and scavengers and raising temperature of tank to 115° F.