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.
US Migratory Bird Act: no special status
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: vulnerable
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.
Coregonus hoyi is heavily parasitized, with common parasites including: Botriochocephalidae, Nematoda, Trematoda, Cestoda, Acanthocephala
Known Predators:
Coloration is silvery with some pink and purple iridescence, with a greenish tinge above lateral line and a silvery white ventral surface (Downs et al, 1998). These fish are distinctly laterally compressed with greatest body depth in front of dorsal fin. Coregonus hoyi has a long head and small eye, snout short or pointed with terminal mouth, lower jaw protruding past upper jaw with distinct tubercle, and a maxillary extending posteriorly to below the anterior portion of the eye. Gill raker number 37-50. A small dorsal adipose fin is present. The following is a characterizatin of the fins: dorsal 1, rays 9-11; caudal fin distinctly forked; anal rays 11-12; pelvic rays 11; pectoral rays 15-16. The scales are cycloid. It has 55-57 vertebrae. Females reach a slightly larger size than males (Crossman and Scott, 1973).
Average mass: 227 g.
Average length: 23 cm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: female larger
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.
Range lifespan
Status: wild: 9 to 11 years.
Average lifespan
Status: captivity: 10 years.
Bloaters exist in both pelagic and 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.
Range depth: 10 to 180 m.
Average depth: 40-110 m.
Habitat Regions: freshwater
Aquatic Biomes: pelagic ; benthic ; lakes and ponds
Coregonus hoyi is endemic to the Great Lakes basin of North America where it inhabited all lakes except Lake Erie. This species was probably extirpated from Lakes Ontario and Nipigon and is threatened in Lake Michigan and declining in Lakes Superior and Huron.
Biogeographic Regions: nearctic (Native )
Coregonus hoyi is primarily a pelagic feeder, with occasional bottom feeding, but habits and diet appear to be variable between bodies of water. Analysis of stomach contents revealed primarily Mysis relicta and Pontoporeia affinis, both near bottom dwelling plankton. Copepods dominated some stomachs, indicating pelagic feeding. Fish eggs and fingernail clams were also found in some stomachs. Vertical migration on an individual basis is hypothesised to be driven by migration of invertebrates in the water column (TeWinkel and Fleischer, 1999). High potential feeding rates at cold temperatures allow bloaters to feed and grow during the winter when many competitors are inactive. Increased activity at cold temperatures also allows the bloater to take advantage of high early spring zooplankton abundance which its competitors cannot do.
Foods eaten: Mysis relicta, Pontoporeia affinis, Cyclops bicuspidatus, Diaptomu, copepods, fish eggs, fingernail clams
Animal Foods: eggs; mollusks; aquatic crustaceans; zooplankton
Primary Diet: carnivore (Eats eggs, Eats non-insect arthropods); planktivore
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.
Coregonus hoyi is an important component in the diet of larger salmonid species. Many of these salmonids are very valuable as gamefish, bringing economic benefit to the waters they inhabit. As the larger ciscoes have been depleted through overfishing, the smaller Coregonus hoyi has become an increasingly important component of commercial catches. Commercial catches of Coregonus hoyi, like other ciscoes are primarily smoked and distributed for human consumption.
Positive Impacts: food
Bloaters have no known negative impact on people.
Coregonus hoyi remains in the larval state for aproximately 24 days with a length range of 8.6-14.9 mm. Larvae are most frequently located near the bottom at depths between 90 and 110 m in water with temperatures not exceeding 4.7 degrees C. Mature C. hoyi reach lengths of 200-250 cm, with size and growth rate variable between lakes.
Development - Life Cycle: metamorphosis
Perception Channels: tactile ; chemical
Spawning generally takes place in February and March, but some spawning occurs throughout the year as indicated by observations of ripe, nearly ripe, and spent male and females in almost all months. Spawning occurs over almost all bottom types at a depth between 36 and 90 m. Egg production ranges from 3000 to 12000 per female, with larger females producing more eggs than smaller individuals. The average number of eggs per ounce of fish is 1241 with little variation. The eggs are relatively large with an average diameter of 1.95 mm.
Breeding season: February -March
Range number of offspring: 3000 to 12000 eggs.
Average number of offspring: 7500.00.
Key Reproductive Features: seasonal breeding ; sexual ; fertilization (External )
There is no parental care in this species.
Parental Investment: no parental involvement
Coregonus hoyi, also known as the bloater, is a species or form of freshwater whitefish in the family Salmonidae. It is a silvery-coloured herring-like fish, 25.5 centimetres (10.0 in) long. It is found in most of the Great Lakes and in Lake Nipigon, and inhabits underwater slopes. This fish is not to be confused with the extinct deepwater cisco (Coregonus johannae), a large fish that shared a common name with the bloater.
The bloater is a small, silvery-coloured whitefish with a pink and purple iridescence. It has a greenish tinge above, and a whitish belly.[2] It is very similar to the kiyi, from which it may be distinguished by its lighter upper lip and smaller eye.[3] Its body is deepest at its middle, it has small and pale fins,[4] and it has 40–47 long gill rakers.[3] The discoverer of the bloater, P. R. Hoy, thought it to be "the most beautiful of the white fish".[2] It reaches a maximum total length of 37.0 centimetres (14.6 in) and commonly is 25.5 centimetres (10.0 in).[5]
The bloater is native to all of the Great Lakes (except Lake Erie) and in Lake Nipigon. Across its range it is in decline, and it is listed as Vulnerable to global extinction by the IUCN Red List.[1] It was extirpated in Lake Ontario and is extirpated in Lake Nipigon, is uncommon in Lake Michigan and is in decline Lakes Superior and Huron.[3][4] This decline is caused mostly by predation by the alewife,[6] and also by sea lamprey predation[7] and pollution.[8]
However, efforts to re-introduce the species in to Lake Ontario have been met with great success.[9] Multiple North American fishery agencies have aided in the bloater's return to the lake, due to the positive impact it could have on its food web. Recent studies have shown that this fish has made a surprising comeback, and it is now re-established in Lake Ontario.[10] State, provincial and federal agencies aim to stock 500,000 Coregonus hoyi into Lake Ontario by the year 2015.[11]
The specific epithet of the bloater is given after Dr. P. R. Hoy of Racine, Wisconsin. Dr. Hoy collected the first specimens of this species in 1870 while dredging in Lake Michigan at least 16 miles (26 km) off Racine, at depths of 50 to 70 fathoms (90–130 m). Hoy did not describe the fish himself, but had ichthyologist James W. Milner name the species.[12] Milner placed it in the genus Argyrosomus, now considered a junior synonym of Coregonus, the genus in which the bloater is now placed.[4] The generic name Coregonus, given by Carl Linnaeus in his 1758 tenth edition of Systema Naturæ, is derived from Greek and means "angled eye", referring to the tilted pupil of whitefishes.[13] It is closely related to the cisco or lake herring, Coregonus artedi, and the shortjaw cisco, both of which it is known to hybridise with.[2] The common name of the bloater comes from the swollen appearance it has after being brought up from the deep waters it inhabits.[3] The same name is given to certain type of smoked herring in Britain, which is swelled in its preparation.[14] The bloater is one of the several taxa in the Coregonus artedi complex of freshwater whitefishes, which sometimes all are considered to belong to a single species.[15]
The bloater is found at depths of 30 to 198 metres (98 to 650 ft).[5] There it inhabits underwater slopes, and is tolerant of temperatures between 34.7 and 52.4 degrees Fahrenheit (1.5 to 11.4 Celsius). When it is brought to the surface its gas bladder expands, giving it a swollen appearance.[2]
The bloater feeds mostly on animals living at the lake bottom (zoobenthos), but will sometimes eat small drifting animals, or zooplankton. The shrimp Mysis diluviana, and the amphipod Diporeia hoyi, also named after P. R. Hoy, are recorded as food items.[5] The lake trout, various species of introduced salmon, and the burbot all are known to prey on the bloater.[5] In the nineteenth century it was abundant, and was often caught by fishermen, among whom it was known as the "moon-eye". It was considered a good panfish, but too small to be marketable.[12] Since most of the other "chubs" of the Great Lakes have become extinct, the average size of the bloater has increased, and it is caught and smoked in the United States. The bloater is ignored by sport fishermen, since it is small and found at great depths, and it has too small of a mouth to be used as bait.[7]
Spawning occurs all year round, but is usually in the winter or autumn. Spawning occurs at depths of 37 to 92 metres (121 to 302 ft).[16] The amount of eggs produced by the female varies depending upon her size, and ranges between 3,230 and 18,768.[16] Eggs incubate for 4 months, and bloaters are 1.01 centimetres (0.40 in) in length at hatching.[16] Larval bloaters head to the cool bottom of lakes before becoming pelagic,[16] and by their first summers they become bottom-dwellers.[5] Larval bloaters have a high mortality until they become large enough to avoid predation by other bloaters and alewives.[17] It is slow-growing, because of the scarcity of food in its habitat.[7] The bloater's average length at maturity is 18.3 centimetres (7.2 in), and maximum age reported from otoliths is 10 years.[5]
Coregonus hoyi, also known as the bloater, is a species or form of freshwater whitefish in the family Salmonidae. It is a silvery-coloured herring-like fish, 25.5 centimetres (10.0 in) long. It is found in most of the Great Lakes and in Lake Nipigon, and inhabits underwater slopes. This fish is not to be confused with the extinct deepwater cisco (Coregonus johannae), a large fish that shared a common name with the bloater.
