The aggressive Shore Crab , Carcinus maenus , has a particularly varied diet. On the shore, it is frequently found with a polycheate worm in its claws. It is generally regarded as undesirable because large crabs will prey upon the more delicate animals. Shore Collection Shore collectors will have access to a range of molluscs , worms and crustaceans found in the littoral zone. Tropical aquarists are warned against using most of these foods because of the likelihood of introducing disease organisms.
Parasites occur as free-swimming animals.
Anemones contain seawater and could be responsible for introducing pathogens into the tank. Gamma-irradicated frozen natural foods from aquarist shops, provide a useful alternative diet. My observations on British rock pool fish indicate that parasites are regularly present. Pragmatically, the most sensible procedure is to ensure healthy conditions in the aquarium. Most parasites only become unsightly, and a danger to the fish if it is already weakened by poor husbandry.