Endocrinology of sound production in fishes

Abstract

Fish sounds are often associated with agonistic and courtship behavior, and in many cases sounds are produced by males with sexually dimorphic sound‐producing mechanisms. This review focuses on the sounds and sexually dimorphic sonic neuromuscular system of the oyster toadfish Opsanus tau, compares it with findings on a related toadfish, the midshipman Porichthys notatus and finally reviews data on steroid levels and their effect on seasonal changes in mass of the sonic muscles and sound characteristics in the weakfish Cynoscion regalis. Highlights of the work on the oyster toadfish include the following. (1) Quantitative seasonal changes in the male boatwhistle mating call in a manner suggesting that steroids modulate the output of central nervous system pattern generators for fundamental frequency and duration. (2) Larger sonic muscles in males comprised of a greater number of smaller and therefore more energy efficient fibers than in females. Male muscles have greater activities of anaerobic and aerobic enzymes and enzyme activities and muscle size are increased by andro‐gens. (3) Neurons in the spinal sonic motor nucleus (SMN) are small in females and either small (S) or large (L) in males. The same three morphs are present in Porichthys, but there are major differences in somatic growth patterns, dendrite development and sonic abilities among morphs in the two species. Development of sexual dimorphism in the SMN suggests major differences between amniotic vertebrates (birds and mammals) and fishes, particularly with regard to perinatal critical periods and cell death. (4) As in other vertebrates, toadfish sonic centers in the central nervous system (including the supracommissural nucleus of the ventral telencephalon, nucleus preopticus parvocellularis anterior, the torus semicircularis and the inferior reticular nucleus) possess gonadal steroid‐concentrating neurons. Although endocrine investigation of sound production has been attempted in only three species, its relevance to important life history events of commercially‐important species and the availability of large numbers of basic biological questions suggest the field is ripe for further investigation.