Hydroid Gonothyraea loveni found on the straightnose pipefish (Nerophis ophidion) in the Gulf of Gdańsk — symbiosis, parasitism or biofouling?

Straightnose pipefish (Nerophis ophidion), covered with hydroid Gonothyraea loveni, were caught in August 2010 near Gdynia while fishing with fyke nets. The hydroid colonies were spaced around the fish, from the head to the anus. These colonies seemed to cause serious problems with the balance and swimming ability of the fish. It appears that there are no symbiotic or parasitic relationships between the hydroid and the fish. The fish was probably just another substrate for G. loveni and became colonized by fouling on the skin surface. It should also be taken into consideration that hydroid colonies can move from place to place with their fish host. It is possible that the hydroid benefits from the fish active search for planktonic food.