Cod courtship song: a song at the expense of dance?

摘要

The reproductive behaviour of cod (Gadus morhua) is described. The mass of drumming muscles, used to produce sound, but not fin size, used in displays, was sexually dimorphic, with males having larger muscles than females. Cod caught off northern Norway were parasitized by the copepod Lernaeocera branchialis infecting the gills, metacercariae of Cryptocotyle lingua in the skin, adult digeneans (Hemiurus levinseni and Derogenes varicus) in the stomach, the acanthocephalan Echinorhynchus gadi in theintestine, and anisakid larvae in the liver, caeca and stomach. The parasite index for males was positively related to both mass of drumming muscles and fin size. A positive relationship between parasite index and fish body mass was also found, but whenbody mass was controlled for, the associations between parasite index and the morphological characters examined disappeared. In females, no significant relationship was found between parasite index and fish body mass, mass of drumming muscles or fin size. Therefore, the size of these characters in males need not be influenced by the need to transmit information about heritable parasite resistance as an indirect benefit to mate-seeking females. However, variation in fertilization potential (spermatocritlevel) among males was related to both mass of drumming muscles and fin size.