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Vimba (Vimba vimba)
Order: Cypriniformes Family: Cyprinidae
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Foto: Ari Saura |
Description: The vimba is a moderate-sized cyprinid with an elongated and laterally flattened body. It has an inferior, crescent-shaped mouth with thick lips. There are 56−61 scales on the lateral line. The anal fin generally has 19 branched soft fin rays (21−24 fin rays in total) and a forked outer edge. Along the midline of the back, there is a low keel-like ridge. The sides are normally silvery and the belly is white, except during the spawning period when the male in particular has dark, bluish-grey or sooty-coloured flanks and an orange belly.
Origin and distribution: Three subspecies of vimba, which probably diverged during the latest glacial period, have been recognized within the range of the species. The subspecies occurring In the Baltic basin is known as V. vimba vimba. In Finland, the vimba is an anadromous fish, and there are no landlocked populations like those in the neighbouring Baltic countries. On its spawning run, the vimba ascends some 30 rivers discharging into the Gulf of Finland and the Archipelago Sea and into the Gulf of Bothnia south of the Quark. Shoals of vimba tend to favour coastal waters.
Reproduction: In Finland, vimba spawn for the first time at 7−8 years of age, when they are about 25 cm long. Adults migrate to the lower reaches of rivers close to the spawning grounds in May, and wait for the rise in water temperature that will induce the final maturation of their gametes. Males even rub stones and gravel in the spawning grounds to clean them of silt. The spawning grounds are small and in places have a swift current, e.g. in rapids or on sandbanks. Spawning begins once the water temperature has risen to 13−15 ºC. Spawning is intermittent; it may take place in two or three acts and the period may extend to the middle of June. The larvae hatch after about a week, first hiding on the bottom for a few days before leaving. At 2−3 weeks they can be seen swimming upstream in schools, searching for suitable habitats. Young-of-the-year vimbas probably descend to the sea in late summer or in the autumn.
Diet, growth and migrations: Vimba feed on benthic invertebrates, such as amphipods, small gastropods, insect larvae and bivalves, Macoma baltica in particular. They can reach a length of 30−45 cm and an age of at least 15 years. The maximum weight of vimba in the Baltic is 1.0−1.4 kg. Tagging of adults in Estonia has proven their fidelity to the spawning river; probably as a sign of homing. In Finland, the spawning runs of vimba have been quite short, but elsewhere migrations of several hundreds of kilometres have been reported. During their spawning run, vimba may leap at least a metre out of the water in order to pass weirs.
Fishing and catches: The vimba was a highly valued fish in the early 20th century and was caught in large amounts with lift-nets and by angling during its spawn in the rivers Paimionjoki, Karjaanjoki and Porvoonjoki. It was also caught in winter with gillnets near the city of Pori. Then the majority of stocks collapsed and, today, there is no fishing for vimba in Finland. Small amounts of vimba are taken as by-catch of pikeperch fishery, but the species has no commercial value. Official catch statistics do not recognize vimba catches.
Vulnerability, threats, and management: Vimba populations collapsed in the late 20th century throughout the Baltic basin. Damming of rivers and dredging of rapids destroyed a large part of the spawning grounds for vimba and the habitats of larvae in Finland as elsewhere. Water pollution and excessive fishing may have contributed. In Finland, little has been done to promote recovery of the species. Most populations are declining and some of them have even been lost. Since 1985, also in the latest evaluation in 2000, vimba has been classified as a near-threatened (NT) species. Recently, the building of fish-ways and demolition of dams have improved the conditions for the vimba's spawning run in some rivers. Enhancement of stocks would require more rehabilitation of spawning rivers, and possibly artificial reproduction as a first step.
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