Species Profile: Yellow Perch, Perca flavescens - SRAC Fact Sheets

Figure 2. <strong>Yellow</strong> perch, <strong>Perca</strong> <strong>flavescens</strong>. soft rays. The pectoral, pelvic and anal fins are supported by one to three spines followed by a series of soft rays. Natural history <strong>Yellow</strong> perch belong to the largest group of fish—the spiny-rayed fishes, order Perciformes. This group includes more than 9,200 species, most of which occur in marine inshore habitats. Fewer than 20 percent of these species live in freshwater, although slightly more may live in freshwater part of their lives. The perch family, Percidae, consists entirely of freshwater species that are distributed in the temperate and subartic zones of the Northern Hemisphere. In addition to the yellow perch, this family includes other well-known North American commercial and sport fish such as the walleye, Sander vitreus, and the sauger, Sander canadensis, as well as numerous species of small stream fishes called darters. originally include river drainages entering the Pacific Ocean or the Bering Sea. The species has since been introduced into nearly every state in the U.S., though some states now limit or prohibit yellow perch introductions. Culturists considering yellow perch should consult state authorities. 3a Reproduction <strong>Yellow</strong> perch are spring spawners that mature during late fall or winter and lay their egg masses when daylength increases and temperature rises. Spawning usually peaks at about 10 °C (50 °F). Most spawning occurs in March and April, although it may peak as early as December or January in some southeastern states. The females release a unique gelatinous, accordion-like strand of eggs called a “ribbon” (Fig. 3). As many as four or five males may fertilize the eggs in the tube-like matrix, which is slightly heavier than water. The micropyles of the eggs reportedly face inward, so the sperm must penetrate the matrix openings to complete fertilization. The egg strand or ribbon may become entangled on vegetation or debris in the water, or it may settle to the bottom of rivers or streams. The ribbons can be more than 6 feet long and are proportional to the size of the female. Fecundity varies with fish size, age and nutritional status, but most females lay about 120 to 250 eggs per mm of their length. A more precise estimate of the fecundity of yellow perch from Lake Erie was given as log (fecundity) = -4.119 + 3.629 x log (total length in mm) (from Great Lakes Fisheries Commission Technical Report 39). <strong>Yellow</strong> perch females have a distinctive gonadal structure. The single ovary develops from a paired structure that fuses during the fish’s early development. The ovary is blunt and rounded at the anterior end and tapers toward the posterior end. The testes of male perch are paired and elongate, like other species of fish. Until the fish are mature, it is difficult to distinguish between the sexes on the basis of external characteristics. Range The original range of yellow perch included freshwater and some brackish water habitats from Nova Scotia southward to South Carolina, westward to Kansas and the Montana border, then northwest into Canada, throughout Alberta, and to the southern portions of the Northwest Territories. <strong>Yellow</strong> perch historically occurred throughout the Canadian provinces bordering the U.S., with the exception of British Columbia. Their range did not Figure 3a. <strong>Yellow</strong> perch egg mass or “ribbon.” Figure 3b. Magnified perch eggs showing embryos. 3b

Differentiation of the gonads of yellow perch begins in fish as small as 10 to 12 mm (about 0.5 inch) long. Some yellow perch males may mature in their first year, but most mature at age 2 or older. Most wild perch females mature at age 3 or 4 years. In culture settings, a higher percentage of females will mature at age 2. <strong>Perch</strong> show a sexual dimorphism in growth that can be detected 60 days or less after hatching. Female perch grow faster than males, but yellow perch grow more slowly than most other species, requiring a year or more to reach the preferred harvest size of 110 to 150 grams (0.25 to 0.3 pound). <strong>Yellow</strong> perch may live up to 10 years and may reach a maximum size of 1.0 to 1.5 kg (2 to 3 pounds) in optimal conditions. However, most perch live only to about 5 years of age, particularly in the southernmost areas of their original range. Adult perch do not care for the eggs or larvae. The eggs hatch after a temperature-dependent incubation period, typically about 3 weeks. Larval perch are active swimmers and initially show a positive phototaxis, moving toward the surface or brighter light sources. The larvae feed on very small zooplankton or zooplankton larvae, including rotifers, copepod nauplii and smaller cladocerans. As they grow, the small perch consume larger zooplankton, insect larvae and other benthic organisms, and eventually small fish, including other perch. During early life stages, yellow perch are cannibalistic, particularly when food is limited. <strong>Yellow</strong> perch consume a wide range of organisms during their lives and are quite adaptable to a variety of foods and habitats. They feed almost exclusively by sight, and primarily at dusk and dawn. Culture techniques Spawning <strong>Yellow</strong> perch have a single spawning period each year. They lay eggs when the arrival of spring brings rising temperatures and longer photoperiods. Depending on the latitude, yellow perch may spawn as early as January in North and South Carolina and as late as June in northern Canada. <strong>Yellow</strong> perch must be exposed to cold temperatures for their eggs to develop and mature. In the states bordering Canada and northward, the maximum temperature for this “chill period” is as low as 6 °C; it may be closer to 10 °C (50 °F) at the southernmost fringe of perch distribution. The necessary duration of the exposure to cold temperatures was determined to be at least 185 days for fish in Minnesota, but the optimum exposure time for perch from other areas is unknown. In general, yellow perch from more southern latitudes do not require a period of cold exposure that is as long or as cold as that needed by fish from more northern areas. Researchers and culturists have successfully manipulated the spawning time of yellow perch by compressing or extending the reproductive cycle, but the results have not been entirely satisfactory from a culture perspective. Male yellow perch respond favorably to a compressed, extended or shifted photo-thermal cycle. But females have exhibited poor egg quality, asynchronous oocyte maturation within the ovary, or little change in spawning time at all. The most promising approach for making eggs available throughout the year is believed to be shifting the photo-thermal cycle so that the cold period occurs at different times of year for different groups of perch. <strong>Perch</strong> may need to be exposed to the offset annual photo-thermal cycle beginning in their first year. <strong>Yellow</strong> perch spawning can be done manually or naturally. Most yellow perch production in the U.S. still depends upon eggs produced through “natural spawning” by stocking adult perch in culture ponds, by transferring egg ribbons collected from ponds or lakes (wild or captive) into fertilized ponds, or by collecting fin- gerlings from extensively managed ponds containing perch broodstock. More commercial culturists are using artificial spawning and tank incubation of fertilized eggs to better synchronize larval production (which reduces cannibalism), improve hatching success, and allow more accurate enumeration of larvae. When a female perch is ready to spawn, the abdomen is swollen and becomes flaccid and the vent will protrude and may appear sac-like. At this point, the spawning period of a group of perch can be shortened from about 3 weeks to only 3 or 4 days by administering chorionic gonadotropin (e.g., Chorulon®) or an analogue of gonadotropinreleasing hormone (GnRHa). GnRHa is not currently approved by the FDA for use with this species, but it is being considered and it may be available under an investigational new animal drug application (INAD). After hormone treatment, the fish will need to be examined frequently for ovulation. Or, they can be tank spawned if maintained at low densities with two to four ripe males per female. Fertilization is more consistent with manual spawning, however. Manual spawning of yellow perch requires some experience and skill because of the unique egg ribbons. Applying gentle pressure on the abdomen of a female that has ovulated will cause the egg strand to be expelled in one mass. Eggs can be fertilized with a wet or dry method as long as there is adequate contact by the sperm throughout the egg ribbon (the micropyle openings face the inside of the egg ribbon). Egg ribbons incubated in tanks must be suspended on wires or racks to allow adequate water circulation through the eggs. Incubation time for perch eggs is 95 to 108 degree-days (C) above 5 °C (41 °F), or about 12 days at 13 to 15 °C (55 to 59 °F). Temperature should be increased gradually to the optimum hatching temperature of 15 °C (59 °F). The methods and facilities used to incubate fertilized perch eggs are determined by the approach used to grow the fingerlings.