Rearing Male Bluegills Indoors May Be Advantageous for Producing Food-size Sunfish

—An indicated demand for sunfish (Lepomis spp.) as a food fish remains untested because of continuing inability to efficiently rear these fishes to required large sizes ($227 g; 0.5 lbs). A recent study involving parallel, indoor rearing of two sunfishes under favorable conditions showed that bluegills Lepomis macrochirus possessed markedly higher growth capacity than B3Ghybrids (F1: male bluegill 3 female green sunfish, Lepomis cyanellus). B 3 G hybrids had been thought to possess superior growth capacity and so have received more attention than bluegills as a food-fish candidate in many areas of the USA. Reanalysis of data from the recent study with emphasis on gender differences revealed that the male bluegills possessed much higher growth capacity than male B 3 G hybrids, at least from May to March as Age 1 and then earlyAge 2fish.Male bluegills reached 67% of food-market weight within the 10-mo period from a starting weight of 7 g; male B 3 G hybrids reached only 24% of this weight.Male bluegills’ more rapid growth versus male B 3 G hybrids’ apparently involved less growth energy allocation to gonad development. Female bluegills grew slower than male bluegills but also outgrew male and female B 3 G hybrids whose growth trajectories declined in midsummer (June) and remained largely flat through March. The previous view that B3G hybrids possess higher growth capacity than bluegills was fostered by studies in pondswhere bluegill growth can be impeded by high reproduction rates and, as this study reveals, by high densities and exposure to suboptimal temperatures when their growth potential is high. Indoor rearing ofmale bluegills should amelioratemost pondrelated growth impediments and take fuller advantage of their rapid growth capacity. Fish of the genus Lepomis, including some of their hybrids (collectively, sunfish), have long been reared mainly to small and intermediate sizes for recreational pond stocking throughout much of the USA (Flickinger et al. 1999; Heidinger 1999; Brunson and Morris 2000). More recently, demand has developed for large sunfish ($227 g; 0.5 lbs) as food fish (Chopak 1992; NCRAC 1999; Brunson and Morris 2000). Sunfish approaching food-market size are also desired by fee-fishing operations and by fisheries management agencies for warm-water stocking programs (Brunson and Morris 2000). Although a handful of commercial producers have reared sunfish for food markets (Morris and Mischke 2000; R. Butz, Windridge Farm, Germantown, MD, USA, personal communication), techniques for the efficient rearing of large sunfish are not well established (NCRAC 1999; Loveshin and Matthews 2003). The consensus view of the North Central Regional Aquaculture Center’s Sunfish Workgroup is that capacity to rear sunfish to $227 g within a 2-yr period of grow out must be achieved for their commercial production as food fish to become viable (R. Hayward, University of Missouri–Columbia, Columbia, MO, unpublished results). This time limit is consistent with maximum tolerable rearing times for a number of food-fish species (Loveshin and Matthews 2003). Sunfish culture, whether aimed at stocking ponds or producing food fish, has remained almost exclusively pond based (Ricker 1948; Schmittou 1965; Lewis and Heidinger 1978; Tidwell et al. 1994; Loveshin and Matthews 2003). Among the sunfishes, bluegill Lepomis macrochirus and the B 3 G hybrid (F1: male bluegill 3 female green sunfish, Lepomis cyanellus) have received the most attention as food-fish candidates (Hayward and Wang 2002). Besides possessing positive marketing qualities, which include good flesh texture and flavor and being well recognized (Webber and 1 Corresponding author. 2 Present address: Piketon Research and Extension Center, Ohio State University, 1864 Shyville Road, Piketon, Ohio 45661 USA. JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 37, No. 4