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The banded killifish ( Fundulus diaphanus) is a North American species of temperate freshwater killifish belonging to the genus Fundulus of the family Fundulidae. Its natural geographic range extends from Newfoundland to South Carolina, and west to Minnesota, including the Great Lakes drainages.Page, Lawrence M. and Brooks M. Burr (1991), Freshwater Fishes, p. 216, Houghton Mifflin, New York. This species is the only freshwater killifish found in the northeastern United States. While it is primarily a freshwater species, it can occasionally be found in brackish water.Werner, Robert G. (2004), Freshwater Fishes of the Northeastern United States, p. 206, Syracuse University Press, Syracuse, New York. .
The eastern subspecies, F. d. diaphanus, can be differentiated from the western subspecies, F. d. menona, by the presence of a further anterior dorsal fin position, increased number of anterior bars in the males of the subspecies (9–15 compared to 5-0 for F. d. menona) with more intense bars along the side that stay intact along the anterior back, a higher number of scale rows (40–44 F. d. menona, 45–49 F. d. diaphanus), and a combined number of dorsal and anal fin rays totaling 24 to 26, compared to 23 to 24 for F. d. menona. Larger maximum sizes have been reported for F. d. diaphanus than F. d. menona.
The banded killifish is similar in habitat preference and appearance to the mummichog, Fundulus heteroclitus, and the two species have been known to interbreed where their habitat overlaps. The banded killifish, while euryhaline, is more commonly found in freshwater, whereas the mummichog primarily inhabits brackish and coastal waters. The two species can be visually identified by the difference in bands; the banded killifish has thin dark bars, while the mummichog has thin light bars. The species can also be differentiated by the thicker caudal peduncle in the mummichog and branchiostegal rays often numbering 6,6 for the banded killifish (5,5 in the mummichog). Banded killifish have larger and more numerous gill rakers compared to mummichogs (8–12 vs. 4–7, respectively).
The Waccamaw killifish, Fundulus waccamensis, is a closely related species to the banded killifish that is endemic to Lake Waccamaw, North Carolina, and its tributaries. the Waccamaw killifish differs by its slimmer profile; the ranges of the two species do not overlap.
The population of banded killifish in Newfoundland was assigned a status of special concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) due to biogeographical isolation and limitation of potential for range expansion. In the United States, Ohio and Illinois list the western subspecies as endangered and threatened, respectively, due to range expansion of the eastern subspecies which has been documented to hybridize wherever the ranges of the subspecies overlap. As such, Ohio also classifies F. d. diaphanus as an injurious aquatic invasive species. Intergrades occur in the Saint Lawrence and Lake Erie drainages where the ranges of the two subspecies naturally come in contact.
The banded killifish has been introduced outside of its native range in the states of Idaho, Ohio, Oregon, Pennsylvania, South Dakota, Washington, and West Virginia. In Oregon and Washington, the western banded killifish is reported to be the introduced subspecies.
Banded killifish are euryhaline, but they usually inhabit freshwater streams and lakes. The largest adult recorded, observed in Indian Bay, Canada, was . People have used banded killifish as Fishing bait. Most people do not favor them as pets because they require a high level of maintenance and therefore do not survive well in an aquarium setting. They are important to aquatic because they are a food source for larger fish such as largemouth bass, northern pike, and trout. They are also a food source for birds such as belted kingfisher ( Megaceryle alcyon), common merganser ( Mergus merganser), and .
In January 2005 the banded killifish was listed as a vulnerable species under the Newfoundland Labrador Endangered Species Act and the Canada Species at Risk Act (SARA) for the Newfoundland population. This species is facing habitat degradation due to industrial development, motorized watercraft activities, and removal of aquatic vegetation.
Spawning occurs at water temperatures of . The male chooses a site in the shallow part of the water and protects it from other males. When a female appears, the male will court the female and fight with the other prospecting males. The female will emit one egg while the male pursues her. Once together, the female emits 10 eggs that falls onto the bottom or gets attached to aquatic plants in the chosen spawn area. The male will continue to pursue the female until the female have laid 50 to 100 eggs.
A single female may lay several clutches of eggs during one summer. After the eggs have been fertilized, both the parents will leave and go their separate ways; the eggs do not receive parental care. Juvenile fish ( in length) emerge within 10 to 12 days depending on the temperature of the water. They reach maturity at approximately 1 year with an average length of . Banded killifish can live for a little over 2 years. However, there have been some that have been observed to live up to 3 years.
The nutritional state of banded killifish influences individual's decisions to shoal or not. Food-deprived individuals spent more time by themselves and not in shoals. When food-deprived individuals were found in shoals their shoals were not any smaller than that of a well-fed banded killifish. Hungry banded killifish are more likely to leave a shoal than a well-fed individual. In the presence of a food stimulus, group size decreases, so that each individual does not have to Competition with others for access to these resources. When presented with food odour, individuals were less attracted to neighbors, but when presented with a predatory stimulus, they were more attracted to neighbors and formed tighter shoals. When in the presence of both stimuli, the group size is intermediate.
In the presence of a predatory stimulus, banded killifish decrease the amount of food attempts and duration of feeding posture. This is done to allocate more energy to predatory Alertness and avoidance. In both the presence and absence of predatory stimuli, banded killifish feeding rate for individuals is independent of shoal size. Lone individuals incur additional cost because they do not gain the improved predatory protection granted by shoal formation, and thus will attempt to join larger shoals rather than smaller shoals. When deciding whether to join a shoal or not, banded killifish value predatory protection over foraging opportunities.
Besides the dilution effect, shoaling also benefits the individual because of group vigilance. To best protect against predation, the banded killifish must be on the lookout to detection predators. In a group, each individual can spend less time looking out for predators because others in the shoal can share in this responsibility. With increasing shoal size, each individual spends less time being vigilant, but with more individuals the group increases overall vigilance and therefore benefit each individual in the shoal. When one individual detects a predator, an Alarm signal is made to alert the shoal, so that the individuals can act to protect themselves from predatory attack.
To improve predator avoidance, banded killifish will often take refuge. Frightened fish in the presence of a predatory stimulus will hide in a foodless refuge. This preference is modulated by individual body size. Larger individuals spend more time in the refuge than their smaller conspecifics. Smaller banded killifish individuals are more prone to risk than their larger counterparts.
Banded killifish use body coloration to determine if an individual has been Parasitism or not. Black spots indicate the presence of a parasite, whereas the absence of these spots indicates an unparasitized individual. Both parasitized and unparasitized individuals preferred to join unparasitized shoals. The preference for unparasitized shoals increases with an increase in parasite load of a parasitized individual.
Shoaling preferences in banded killifish differ in shoal species composition, shoal size, and individual body size within the shoal. The shift in preferences is triggered by predatory stimuli. In the presence of predatory stimuli, a banded killifish individual will prefer the bigger conspecific shoal, but only as long as the shoal is homogenous in individual fish size. If the size of individual fish were different, they would join a shoal of similarly sized fish regardless of shoal size. This preference is maintained by predatory threat. Body size is a more significant determinant of shoaling preference than shoal size and species composition.
Banded killifish have been found to engage in heterospecific shoaling with other species of killifish as well as other fish. There are many situational factors that determine if the banded killifish individual would want to engage in heterospecific shoaling. If body size is similar, then banded killifish prefer conspecific shoals as opposed to heterospecific ones. Size is a sorting mechanism for conspecific as opposed to heterospecific shoaling.
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