Hybrid Sunfish

SRAC Publication No. 7205

VI February 2007 PR

Species Profile: Hybrid Sunfish

Charles C. Mischke1, Joseph E. Morris2 and Ryan L. Lane3 Bluegill (Lepomis macrochirus), greater tolerance of cooler water However, widespread introductions redear (L. microlophus) and green temperatures and poor environmen- have increased the ranges of these sunfish (L. cyanellus) are the most tal conditions, and greater vulnera- sunfish throughout the country. common of the 11 sunfish species. bility to angling. Because of these The first researchers observed the Sunfish are important forage fish particular characteristics, there is basic biological activities of sun- throughout the United States. Since much interest in culturing hybrid fish. These early studies found that the 1930s sunfish, primarily sunfish commercially both for pond all sunfish begin spawning in late bluegill, often have been stocked stocking and for food fish. spring or early summer and most with largemouth bass (Micropterus continue spawning until early fall. salmoides) and are themselves popu- Spawning and Male sunfish usually appear first at lar sport fish. reproductive activity the spawning sites. Males construct nests in shallow water by sweeping Sunfish are extremely productive, The sunfish family, Centrarchidae, with each female producing an a depression in the sand or gravel. is a strictly North American fish Sunfish are colonial nesters, with average of 80,000 eggs per year family. The native range of the from several successive spawns. nests in densely packed clusters bluegill was in the eastern U.S., (Fig. 1). A male circles its nest and This often results in overpopulation while the green sunfish was found and stunted growth; most fish are produces courtship calls consisting in the central U.S. and the redear of a series of grunts. When a less than 5 inches (12.7 cm) long. sunfish in the southeastern U.S. Producing hybrids is one strategy female is attracted to the nest, her for controlling sunfish overpopulation. Various sunfish species inter- breed readily, so hybrid production is relatively simple. Although hybrid sunfish are not sterile, some specific crosses result in skewed sex ratios (predominately males) and other crosses exhibit abnormal reproductive behavior; both conditions can reduce reproductive potential. However, some sunfish crosses have hybrid vigor that is observed in improved growth rates, greater acceptance of formulated feeds,

1 Mississippi State University, Stoneham, MS 2 3 Iowa State University, Ames, IA Southern Illinois University, Carbondale, IL Figure 1. Sunfish are colonial nesters, constructing nests in densely packed clusters. After spawning the male sunfish defends the nest and cares for the eggs. eggs are deposited and then fertil- able characteristics (skewed sex sary for a positive identification. ized. One female may deposit eggs ratio, rapid growth rate); however, First, use gentle pressure on the into several nests, and more than the reverse cross does not. abdomen, moving from the middle one female may deposit eggs into a Like most fish, sunfish are more of the abdomen back to the vent. single nest. After spawning, the easily sexed during the breeding If milt (white liquid) is expelled female leaves the nest. The male season (Fig. 2). As spawning nears, from the urogenital opening, the remains to defend the nest from males take on distinctive, brilliant, fish is a male. If no milt appears, predators and fan the eggs to keep spawning colors and it is usually the fish is probably a female but them aerated and clean of debris. easy to express milt from the vent. positive identification requires a Different sunfish species—i.e., During the breeding season, the capillary tube. A 0.04- to 0.05- bluegill and redear—are often abdomens of females are fuller and inch-wide (1.1- to 1.2-mm) and 2- found nesting together in the same rounder than those of males. Males to 4-inch-long (5- to 10-cm) capil- colony. tend to be larger than females and lary tube should be used. Hold the Bluegill and green sunfish can have more square-shaped bodies. fish upside down and gently insert the capillary tube through the uro- spawn several times after water Although coloration and appearance temperatures reach 70 ºF (21 ºC). genital opening (Fig. 3). Once the are helpful in determining sex, capillary tube is inserted into the The suitable temperature range for gamete verification is usually neces- bluegill reproduction is 68 to 86 ºF (20 to 30 ºC), combined with a 12- to 16-hour photoperiod. History of hybrid production The earliest research on stocking hybrid sunfish for population control was conducted in the 1940s. Hybrids between female redear sunfish and male bluegill resulted in only 2 percent females, demon- strated good growth rates, and were considered excellent for stocking into small ponds. In the 1960s, all possible crosses between bluegill, redear sunfish and green sunfish were made. The resulting offspring showed different sex ratios. A cross with a female redear sunfish and male green sunfish produced offspring with a 50:50 sex ratio; however, all other crosses resulted in more than 70 percent males. Broodstock: selection of Figure 2. Sunfish are more easily sexed during the breeding season. The male bluegill (below) tends to be larger than the female (above) and takes on distinc- species and tive spawning colors. sex identification When producing hybrid sunfish it urogenital sinus, angle it back is critical to identify both the toward the tail and slightly to one species and sex of the parent fish. side. Then, gently push the tube Many taxonomic keys are available through the oviduct and into the for species identification. Parent ovary. Use gentle force while stock purity is important because slightly twirling the capillary tube offspring viability and performance back and forth. When the tube is will be affected. The sex of a inserted, place a finger over the selected parent species affects the end of the tube and remove it. If

F1 (first generation) offspring per- eggs are seen in the tube, the fish formance and sex ratios. For exam- is a female. If no eggs are present ple, the most common hybrid par- and no milt was expelled, then sex ents are the green sunfish female Figure 3. Inserting a capillary tube cannot be determined and the fish and bluegill male; this cross pro- into the sunfish urogenital opening to should not be used. duces F offspring with many desir- retrieve eggs is the most reliable 1 method for sexing adult fish. Egg and fry production ature and photoperiod to induce sacs for nutrients and energy to spawning. Fish are held in tanks at obtaining food from the environ- There are two main methods of a male-to-female ratio of 1:2 to 1:4. ment. During this stage, nutrients producing hybrid sunfish—stocking Removable artificial substrates are from the yolk sac are depleted and parent species into ponds for nat- placed in the tanks for spawning the larva’s mouth becomes more ural reproduction or artificial pro- (Fig. 4). The artificial nest pictured fully developed (Fig. 5). Larvae will duction through intensive hatchery was made by removing the bottom methods. 2 inches (5 cm) from a 5-gallon Stocking parent species into empty (19-L) plastic bucket and adding ponds is currently the most com- loose pea gravel to the bottom. mon production method. Ponds less than 1 acre (0.4 ha) are pre- ferred. To prevent contamination with undesirable sunfish, dry the spawning pond thoroughly and treat all depressions with approved fish toxicants before filling it and stocking with broodfish. Water Figure 5. At the swim-up stage, larval sunfish must switch from obtain- from surface sources must be fil- ing food from their yolk sacs to tered using a Saran filter to pre- obtaining food from the environment. vent the introduction of undesirable fish. After the pond has been properly prepared, select mature starve if they do not begin to con- male and female sunfish (prefer- sume food at this time. The first ably 2+ years old) and stock them prey items must be small enough into the pond. Stock 2-year-old par- to fit into the sunfish’s mouth (i.e., ent fish at a 1:1 ratio of males to Figure 4. Removable artificial sub- small zooplankton, including females at a rate of 30 to 40 pairs strates can be used during induced rotifers and copepod nauplii). per acre (75 to 100 pairs/ha). Forty spawning of sunfish. Sunfish grow rapidly, and as pairs per acre should yield approxi- mouth size increases, larger prey mately 100,000 fry per acre such as cladocerans, and eventual- (247,000 fry/ha). Parents are Begin with summer conditions ly larger aquatic insects, are con- allowed to spawn naturally in (72 ºF [22 ºC] and16 hours of light) sumed. When reared in the hatch- ponds and the young are raised in and gradually reduce temperature ery, a commercial larval fish feed the same ponds as the adults until and photoperiod to simulate winter less than 250 µm should be fed at they are at least 2 inches (5 cm) conditions (59 ºF [15 ºC] and first, followed by progressively long. 8 hours of light) over a 2-week larger feeds as the sunfish grow. Even though most hybrids have period. Hold fish in winter condi- Hybrids (green sunfish female x been produced in ponds, intensive tions for 4 weeks and then gradual- bluegill male) will survive when hatchery methods also have been ly return them to summer condi- fed commercial feed, but survival successful. Eggs from one or more tions over an additional 2 weeks. is greatly increased when newly mature females of a selected Fish begin spawning on artificial hatched brine shrimp (Artemia) species are stripped into damp substrates 2 to 6 weeks after the nauplii are fed during the first 7 glass Petri dishes. Then milt is completion of the temperature and days. photoperiod manipulation. After stripped from one or more males Grow out of a selected species onto the eggs. spawning, remove the substrates with attached eggs for hatching Or, the testes from males can be Pond culture excised and cut up, diluted with and replace with fresh substrate. de-chlorinated water, and then Using this method, eggs and fry The accepted marketable food size added to the eggs. After mixing can be produced at any time of for sunfish is 8 to 12 ounces (227 milt and eggs, water is added and year. to 340 g). Sunfish require at least 2 the mixture is left for 2 minutes so Eggs in substrate will hatch in 2 to years to reach this size. Recom- fertilization can occur. Fertilized 10 days, depending on the cross mended stocking rates for hybrid eggs are then transferred to clean being produced and the tempera- sunfish grow out is 5,000 to 7,000 glass Petri dishes containing de- ture. Yolk sac absorption and sub- juvenile fish per acre (12,355 to chlorinated water and allowed to sequent swim-up stage (from 2 to 7 17,279 fish/ha) in year 2. Given become water hardened. Then the days post-hatch) also depend on the brood fish stocking rate of 40 fertilized eggs are rinsed with the specific cross being produced pairs per acre (100 pairs/ha), it is water and the glass dishes are and the temperature. Swim-up is anticipated that 100,000 fry per placed in aerated aquaria. the critical stage in sunfish devel- acre (247,000 fry/ha) will be pro- opment because larvae must duced in year 1. Fingerling sunfish A second intensive hatchery prac- should be stocked at 4 inches (10 tice involves manipulating temper- switch from relying on their yolk cm) or larger and graded for size hybrid sunfish grow out. Recir- diameter is recommended to bal- uniformity. Net production of 554 culating systems usually use tanks ance the higher cost of floating to 841 pounds per acre (622 to 942 for production so less land is feeds with the ability to observe kg/ha) can be expected when stock- required than in pond culture. feeding activity. ing hybrids at 3,238 to 5,666 fish Also, recirculating systems use It has been shown that feeding fre- per acre (8,000 to 14,000 fish/ha), much less water than ponds. quency does affect the growth rates with mean survival about 75 per- However, recirculating systems of juvenile hybrid sunfish. cent. In Kentucky, a net yield of have higher fixed costs (e.g., pump- Increasing from one to three daily 1,718 pounds per acre (1,926 ing costs and oxygenation) and feedings increased food consump- kg/ha) was obtained by stocking require more intensive manage- tion and growth rates. The 5,000 fish per acre (12,355 fish/ha) ment and labor than pond culture. appetites of juvenile hybrid sunfish at an initial stocking size of 2.3 Unlike pond production, a nutri- vary with the time of day, and ounces (66 g). When water temper- tionally complete diet is required daily appetite patterns change with ature reaches 72 ºF (25 ºC), fish to grow sunfish in recirculating feeding frequency. Three daily should be fed a 35 percent protein systems. Hybrid sunfish in recircu- feedings produce the highest diet at 3 percent of their body lating systems require dietary growth rates, but it is important to weight per day. crude protein levels of more than know how much to feed each time Cage culture 40 percent. Grow out stocking den- to avoid over- and underfeeding. sities for sunfish in recirculating Cage culture of hybrid sunfish systems have not yet been deter- Environmental conditions might be an attractive and viable mined. In an earlier NCRAC-fund- for growth option in areas where regular pond ed project, stocking densities of 1.7 culture would not be practical. pounds per gpm (0.2 kg/Lpm) did Optimal temperatures for sunfish Irregularly shaped ponds, quarry not result in marketable fish with- growth are 68 to 86 ºF (20 to pits or other bodies of water that in 30 months of stocking age-1 30 ºC). Most sunfish also spawn cannot be seined easily are poten- fish. when temperatures are in this tial sites. Cage culture requires a range. Sunfish growth generally In Iowa, after 17 months in ponds relatively low initial investment increases as temperatures increase and 12 months in an indoor sys- and allows the simultaneous use of up to approximately 86 ºF (30 ºC), tem, hybrid sunfish had not ponds for sport fishing or the cul- and then decrease at higher tem- reached marketable food size, even ture of other species. There is no peratures. The highest specific with repeated grading. This study unwanted fish reproduction growth rate (SGR), 2.35 percent per indicated that there are still practi- because sunfish cannot spawn in day, was recorded at 86 ºF (30 ºC). cal problems in the intensive cul- cages suspended in the water col- ture of hybrid sunfish in recirculat- Temperature affects not only umn. Therefore, fish size can be ing systems. growth, but also survival. Bluegill kept uniform and inventories are eggs hatch at temperatures ranging accurate. Nutrition from 73 to 93 ºF (23 to 34 ºC). The Five hundred sunfish fingerlings maximum hatch rate for bluegill can be stocked into a cage measur- Little is known of the nutritional eggs occurs at 72 to 75 ºF (22 to ing 4 x 4 x 4 feet (1.2 x 1.2 x 1.2 requirements for specific life 24 ºC); this range is similar for m); 2,000 sunfish can be stocked stages and species of sunfish. In hybrids. Fry have more thermal tol- into an 8- x 8- x 4-foot (2.4- x 2.4- x ponds, producers often depend on erance than eggs and juveniles 1.2-m) cage. A more conservative natural food organisms (e.g., zoo- have more thermal tolerance than guideline is to stock six fish per plankton and benthic organisms). fry. cubic foot (200 fish/m3). As However, with high fish densities these natural food sources can be There are no sunfish-specific guide- observed in pond culture, best lines for other water quality para- results are obtained when first-year depleted quickly. Therefore, producers should consider using sup- meters. The broad guidelines rec- stocking densities are reduced for ommended for other warm-water the second year final grow out. As plemental diets to maintain high growth rates. Feeds that contain fish should be used. Alkalinity and with pond-reared fishes, hybrid hardness should range from 50 to sunfish cultured in cages are fed a high levels of dietary protein (40 percent or more) and at least 10 200 ppm as CaCO3 and pH should 35 percent protein diet with an be 6 to 9. Carbon dioxide, un-ion- anticipated mean feed conversion percent dietary lipid (fish oil) improve the growth and produc- ized ammonia, nitrite and hydrogen ratio of 3.54 and a specific growth sulfide should be kept at the lowest rate of 1.03. tion potential of hybrid sunfish. But when natural food is available, possible levels. Recirculating systems a dietary crude protein level of 36 percent is adequate to obtain maxi- Disease If sufficient land or water mum mean harvest weight. A mix Although hybrid sunfish are con- resources are not available, a recir- of floating and sinking forms of sidered hardy in the wild, they are culating system may serve for 1 pelleted feed ⁄8 inch (3 mm) in susceptible to disease when grown at high densities. Bacterial, fungal and parasitic infections often plague cultured populations, regardless of culture method. Columnaris is the most common bacterial infection in sunfish culture, but it seldom causes mortali- ty. Infected fish should be removed rapidly and discarded to prevent horizontal transmission of the disease. Fungal infections can cause mortalities in cultured sunfish. Saprolegnia spp., the most common fungal infection, can be associated with dramatic temperature decreases. To avoid fungal infections, fish should be properly accli- mated to the water temperature for Figure 6. Harvesting hybrid sunfish from cages and recirculating systems is best growth and temperatures relatively easy. should be kept constant. Digenetic trematodes such as black grubs (Uvulifer ambloplitis), white grubs There also is no standard market determine the number of sunfish (Posthodiplostomum minimum cen- weight for sunfish. The weight of a producers in each state, specific trarchi), and yellow grubs marketable food fish varies among species produced, culture methods (Clinostomum marginatum) are com- locations and cultures; however, used, the most commonly used monly found in sunfish. These fish weighing more than 4 ounces markets, and prices received. grubs do not cause significant mor- (110 g) may be classified as mar- Nationally, there are about 485 talities but do affect marketability. ketable food fish. Considerable sunfish producers with about one- It is important to prevent infection weight is lost from filleting as com- fourth of them producing hybrids because infected fish cannot be pared to in-the-round processing (various crosses). Most commercial treated. To prevent grubs, limit (58 vs. 32 percent, respectively); operations use pond culture and bird access and reduce snail popu- therefore, in-the-round cuts may be are located in Texas and lations. more profitable for producers with Wisconsin. The primary markets smaller fish from shorter grow-out for hybrid sunfish are for sport Harvest periods. Sunfish may some day be fish stocking and fee-fishing opera- available in live markets, consider- tions, though some states did Most sunfish producers do not har- ing the popularity of tilapia. report a market for food fish, bait vest fingerlings until the mean and scientific research. The price length of fish is 2 inches (50 mm), Regulations and permitting per pound varies according to the because smaller fish can be source and the local markets, but stressed by handling. Spring or fall Some states may classify sunfish as producers could expect at least is the recommended time for har- game fish and regulate their sale. $1.00 per pound. vesting fingerlings and adult sun- Some states (Wisconsin, for exam- fish because water temperatures ple) have regulations against the The most cost-effective strategies are lower then. Most producers use stocking of hybrid sunfish in public for fingerling production and grow 1 a non-tarred seine (square mesh ⁄4 waters. Given the diversity of state out have not been determined. 1 to ⁄2 in, 6 to 12 mm) for pond har- regulations, aquaculturists should Out-of-season spawning techniques vest. Harvesting cages and recircu- consult with their state authorities can use relatively small amounts of lating systems is easier than har- to determine if there are regula- space with minimal investments, vesting ponds, but large harvests tions on rearing and selling sunfish. but pond culture is probably the tend not to be as practical (Fig. 6). most cost-effective method for The future grow out. Although hybrid sunfish Processing have limited reproductive poten- There is much interest in the inten- tial, some reproduction does occur There is no standard method for sive production and marketing of in ponds. One way to control this processing sunfish. Processing hybrid sunfish for food. However, limited reproduction might be to methods vary by location and sunfish culture on a commercial stock a small number of large- social culture. After scaling, fish scale is a small industry at this mouth bass, channel catfish or may be processed in-the-round time. The North Central Regional other predatory fish during the (eviscerated or head removed and Aquaculture Center (NCRAC) sur- second year of production, so that eviscerated) or filleted (skin on or veyed state aquaculture contacts to F generations are consumed. skin off). 2 The expansion of hybrid sunfish Suggested readings North Central Regional production is limited by the lack of Aquaculture Center Publications proven, profitable and sustainable Dupree, H. K. and J. V. Huner. Office, Iowa State University, production technologies. Future 1984. Propagation of black bass, Ames, IA. research should address marketing, sunfishes, tilapias, eels, and hobby fishes. Pages 119-135 In Dupree, Morris, J. E., C. C. Mischke and R. biological/technical knowledge L. Lane. 2005. Culture and propa- (broodstock management, fry and H. K. and J. V. Huner, editors. Third Report to the Fish Farmers. gation of sunfish and their hybrids. fingerling propagation, grow out Pages 355-372 In Kelly, A. and J. methods and processing proce- U.S. Fish and Wildlife Service, Washington, D.C. Silverstein, editors. Aquaculture in dures), and economics. the 21st Century. American Morris, J. E., C. C. Mischke and D. Fisheries Society Symposium 46, L. Garling. 2002. Sunfish culture Bethesda, MD. guide. NCRAC culture series 102.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Southern Regional Aquaculture Center or the Cooperative Extension Service is implied.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 2005-385-15815 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.