Host Fishes and Reproductive Biolo K Y of 6 Freshwater Mussel Species from the Mobi E Basin, Usa

Host fishes were identified for 6 species of freshwater mussels (Unionidae) from the Black Warrior River drainage, Mobile Basin, USA: Stropkitus subwxus, Pleurohemafurvum, Ptyckobranthus greeni, Lampsilis yrrovnlis, Medionidus arutissimus, and Villosa nebulosn. Hosts were determined as those that produced juvenile mussels from glochidial infestations in the laboratory. The following mussel-fish-host relationships were established: Stropkitus subwxus with 10 species including Cyprinidae, Catostomidae, Fundulidae, Centrarchidae, and Percidae; Pleurobemafurvum with Campostoma oligolepis, Cyprirlella callistia, C. uenusta, Srmotilus atromaculatus, and Fund&s olimceus; Ptyckobrunckus greeni with Etlleostoma brllator, E. doughs-i, Per&a nigroj&iata, and Percina sp. cf. caprodes; Lampsilis pen&is with Micropterus coosae, M. puuctulatus, and M. salmoides; Medionidus acutissimus with Fundulus olivuceus, Etkeostoma doughsi, E. wkipplei, Percina nigrqfusciata, and Percinn sp. cf. caprodes; and Villosa wbulosa with LqOnlis megul$is, Micropterus coosae, M. punctulutus, and M. sulmoides. Funduhs olhuceus served as host for 3 species and carried glochidia for long periods for 2 other species, suggesting that topminnows may serve as hosts for a wide variety of otherwise host-specialist mussel species. Host relationships for the species tested are similar to congeners. Methods of glochidial release, putative methods of host-fish attraction, and gravid periods are described for the 6 species. Kq rmrds: Mollusca, Bivalvia, Unionidae, mussels, host fish, glochidia, life history, conglutinates. Freshwater bivalves of the superfamily Unionacea have a highly specialized life history in which the modified veliger larvae (glochidia) undergo a brief period as obligate ectoparasites on the gills, fins, or other external parts of fish. Glochidia are brooded in the gills of female mussels until mature, then released through the siphons singly or in clusters called conglutinates (Kat 1984). If the glochidia encounter a suitable host, they encyst for a few days to several weeks, metamorphose into juvenile mussels, and then drop off the fish to assume a benthic lifestyle. Glochidia encountering an unsuitable host are rejected by the fish immune system, usually within a few days. Host specificity varies greatly among mussel species. Some species are able to parasitize a taxonomically wide variety of fish species (Trdan and Hoeh 1982), but others can use only a few, usually closely related, species (Zale and Neves 1982, Yeager and Saylor 1995). Knowledge of fish hosts is essential in understanding patterns of distribution and abundance of mussels (Watters 1992) and in developing effective conservation programs. Lack of recruitment in some mussel populations has been attributed to unavailability of proper host fishes caused by human-induced changes in the fish assemblage (Mathiak 1979, Smith 1985). Conservation efforts, whether centered on captive propagation and reintroduction, relocation, or habitat improvement, require comprehensive host information. Knowledge of host fishes is lacking or incomplete for many North American mussels. In particular, there is a conspicuous dearth of information for species endemic to Atlantic and Gulf Slope drainages, including the Mobile Basin. Most species endemic to the Mobile Basin have experienced dramatic range reductions in the last 50 y (Stansbery 1976, Williams et al. 1992). Several Mobile Basin species have become extinct in this century, and 17 species are listed federally (USA) as endangered or threatened (US FWS 1994). Host fish information is needed urgently for conservation and recovery of the remaining Mobile Basin mussel fauna. In this paper we describe determination of hosts, report observations on glochidial release and putative host-attracting behavior, and report periods of gravidity for Lampsilis perovalis, Medionidus acutissimus, Pleurobema furvum, Ptychobranchus greeni, Strophitus subvexus, and Villosa nebulosa. With the exception of S. subvexus, all are endemic to the Mobile Basin. Strophitus subvexus occurs in Gulf Slope drainages from 19971 H OST FISHES OF UNIONIDS east Texas to Florida (Williams and Butler 1994). Although Zale and Neves (1982) and Neves et al. (1985) provided host-fish data for V. nebulosa from the Tennessee River system, these populations are now referred to as V. iris (Williams et al. 1993, Yeager et al. 1994). Pleurobemafirvum and P. greeni are listed as endangered, and L. perovalis and M. acutissimus are listed as threatened by the US Fish and Wildlife Service (US FWS 1994). Strophitus qubvexus and V. nebulosa are considered of special concern and threatened, respectively, by the American Fisheries Society (Williams et al. 1993). These species represent a broad cross-section of unionid diversity including the subfamily Anodontinae (S. subvexus), the tribe Pleurobemini (P:furvum), and the lampsiline clade (L. perovalis, M. acutissimus, P. greeni, and V. nebulosg) (sensu Lydeard et al. 1996).