These fish are silvery, with some pink, purple, and green iridescence. They have narrow bodies and long heads with small eyes. They have two dorsal fins; the dorsal fin near the tail is much smaller than the dorsal fin closer to the head. Adult females are usually larger than males. (Crossman and Scott, 1973; Downs, et al., 1998; Crossman and Scott, 1973; Downs, et al., 1998)
Bloaters are native to the Great Lakes basin of North America. They can be found in every Great Lake except Lake Erie. This species is probably extinct in Lakes Ontario and Nipigon, threatened in Lake Michigan, and declining in Lakes Superior and Huron. (Page and Burr, 1991)
Bloaters exist in both the open water ("pelagic")and bottom ("benthic") regions of deep, freshwater lakes. During the day Coregonus hoyi is found on or near the bottom, but it moves upwards in the water column at night. Bloaters are most abundant between 40 and 110 m, but have rarely been reported as shallow as 10 m and as deep as 180 m. (TeWinkel and Fleischer, 1999)
Bloaters remain in the larval stage for about 24 days. Larvae are 8.6 - 14.9 mm long and generally stay near the lake bottom. Fully grown adults grow to about 200 - 250 cm long.
Spawning generally takes place at the lake bottom in February and March, but may happen year-round in some bloaters. Each female produces about 3000 to 12000 eggs, with larger females producing more eggs than smaller individuals. The average number of eggs per ounce of fish is 1241. The eggs are relatively large with an average diameter of 1.95 mm. (Crossman and Scott, 1973)
There is no parental care in this species.
Females have a lifespan of 10 to 11 years, and reach a slightly larger size than males, which live to an age of 9 years. (Crossman and Scott, 1973)
Coregonus hoyi spends daylight hours on or near the bottom, and rise into the water column to feed at night. Nighttime densities in the water column have been observed at up to 6.61 fish/m^3. These nocturnal migrations are variable with water temperature, light levels, and individual size. Migration patterns allow C. hoyi to maximize growth through increased consumption of Mysis relicta, which also migrates. (TeWinkel and Fleischer, 1999)
Coregonus hoyi mainly eats in the open water, with occasional bottom feeding. Its habits and diet seem to vary from lake to lake. Bloaters eat mainly plankton, copepods, fish eggs, and small clams. Individual fish move to different depths as they feed, perhaps because their food does as well. At low temperatures, bloaters are more active than most fish, which allows them to grow during the winter, when most of their comptitors are inactive. (Rudstam, et al., 1994)
Historically, the main predator of Coregonus hoyi has been the lake trout (Salvelinus namaycush). After parasitic sea lampreys decimated the lake trout populations in the Great Lakes, introduced Pacific salmonids have become the dominant predators of C. hoyi. Populations can also be limited by competition and predation from alewives. (Crossman and Scott, 1973)
Coregonus hoyi is a deep water planktivore that provides an important trophic link between zooplankton and top predators. After initial population declines due to competition with and predation by introduced alewives and rainbow smelt, C. hoyi populations increased greatly in response to alewife and smelt predation by introduced Pacific salmonids. This change in fish community resulted in a shift in dominance from epi- and metalimnetic planktivores (alewife) to a hypolimnetic benthivore (bloater). This can affect the abundance of prey for pescivores, prey abundance for the forage fish, and possibly water clarity and primary production. (Rudstam, et al., 1994)
Coregonus hoyi is a deep water plankton-eater that is an important link in the food chain between zooplankton and top predators. After bloater populations initially declined due to competition with and predation by introduced alewives and rainbow smelt, their populations grew when Pacific salmon were introduced to teh Great Lakes and began to eat alewives and smelt. (Rudstam, et al., 1994)
Bloaters have no known negative impact on people.
Bloaters are an important source of food for salmon. Salmon are very valuable as gamefish, bringing economic benefit to the waters they inhabit. As the larger ciscoes have been depleted through overfishing, the smaller bloaters have become an increasingly important component of commercial catches. Commercial catches of bloaters, like other ciscoes, are primarily smoked and distributed for human consumption. (Crossman and Scott, 1973; Crossman and Scott, 1973)
Overfishing of other species of ciscoes has reduced populations, and shifted more pressure to Coregonus hoyi. Unchecked, this additional fishing effort could devastate Coregonus hoyi populations, as it has done to other ciscoe species. The bloater is not currently given special status under the Endangered Species Act. The IUCN classifies Coregonus hoyi as vulnerable. Fluctuations in the populations of bloaters have been inversely related to the introduced alewive, which competes for resources. Stocking of pacific salmonids in order to control alewive populations has allowed the Lake Michigan Coregonus hoyi population to rise from an estimated 4,000 metric tons in 1974 to 300,000 metric tons in 1987. (Rudstam, et al., 1994)
Courtney Egan (editor).
Matthew Wund (editor), University of Michigan-Ann Arbor.
Daniel Wyns (author), University of Michigan-Ann Arbor.
Binkowski, F., L. Rudstam. 1994. Maximum daily ration of Great Lakes bloater. Transactions of the American Fisheries Society, 123: 335-343.
Crossman, W., E. Scott. 1973. Freshwater Fishes of Canada. Ottawa: Information Canada.
Downs, W., L. Wiland, E. White, S. Wittman. 1998. "Fish of the Great Lakes by Wisconsin Sea Grant" (On-line). Accessed October 28, 2002 at http://www.seagrant.wisc.edu/greatlakesfish/framefish.html.
Miller, T., L. Crowder. 1990. Effects of changes in the zooplankton assemblage on growth of bloater and implications for recruitment success. Transactions of the American Fisheries Society, 119: 483-491.
Page, L., B. Burr. 1991. A field guide to freshwater fishes of North America north of Mexico. Boston: Houghton Mifflin Company.
Rudstam, L., F. Binkowski, M. Miller. 1994. A Bioenergetics Model for Analysis of Food Consumption Patterns of Bloater in Lake Michigan. Transactions of the American Fisheries Society, 123: 344-357.
TeWinkel, L., G. Fleischer. 1999. Vertical Migration and Nighttime Distribution of Adult Bloaters in Lake Michigan. Transactions of Americans Fisheries Society, 128: 459-474.