Effects of the copepod Cardiodectes medusaeus on the laternfish Stenobrachius leucopsarus with notes on hypercastration by the hydroid Hydrichthys sp.

Abstract

Of the laternfish Stenobrachius leucopsarus collected, 2.7% were infected with the copepod Cardiodectes medusaeus. Coincidentally, 2.7% of the copepods were hyperparasitized by a hydroid, Hydrichthys sp. Copepod infection rates increase from Santa Barbara to San Diego, California. This increase may be due to a corresponding increase in the intermediate hosts. A comparison between the size classes of infected and uninfected fish suggests parasite-induced mortality. No relationship between the number of copepods per fish and host length was evident. Copepods were found in multiple infections up to five per host. A gregarious distribution of larval copepods and a nonspecific fibrotic response by the host is suggested. The copepod castrates its host. Multiple infection did not have an additive effect on host egg size nor did the presence of larval nematodes. A comparison of the total caloric content of copepods, infected and uninfected hosts, suggests that the copepod's energy demands on the host are negligible. The copepod appears to promote somatic growth of both female and male hosts.