Scientific name:Tinca tinca
Alternative common names:
Tench is a freshwater fish. They are found in only a few waters in South Africa. They are generally olive green but can also be dark green and reflect a gold coloration of the ventral surface. They have negative impacts on their environments. In places tench are found there is a decrease in other fish species.
Where does this species come from?Europe and western Asia.
What is its invasive status in South Africa?NEMBA 1b in National Parks, Provincial Reserves, Mountain Catchment Areas and Forestry Reserved declared in terms of the protected Area Act.3 for all other discrete catchment system in which it occurs.
Where in South Africa is it a problem?Western Cape
How does it spread?Introduced as a sports fish by angling organisations, Natural dispersal: Can colonise new areas in connected water bodies.
Why is it a problem?Tench compete with native minnows, bullheads and suckers for food and eat large quantities of snails and insect larvae by feeding heavily on snails, which graze on algae, may contribute to algal blooms. Aggressive feeding by tench stirs up sediments, leading to cloudy water.
What does it look like?Description: Tench has 4 dorsal spines, 8-9 dorsal soft rays, 3-4 anal spines, 6-8 anal soft rays and a caudal fin with 19 rays, has a thickset, heavy and laterally-compressed body, with a. The skin is thick and slimy with small scales embedded. It is usually olive-green but at times dark green or almost black, with golden reflections on the ventral surface. The head is triangular, with orange-red eyes and a relatively long rounded snout. The mouth is terminal, small with thick lips and a pair of well-developed barbels, one at each corner of the mouth. Fully grown, T. tinca is 64 cm long and weighs some 7.5 kg. In the male, the first two rays of the pelvic fins are very thick and this fin is long enough to completely cover the anal opening. Most males reach maturity when they are 3 years old, averaging 9.5 cm; females mature at 4 years of age, measuring 12.5 cm. Tench average 20 to 25 centimetres in length, with a deep and slightly compressed body. Fins are dark and rounded, with no spines. Habitat: The Tench avoids fast water and is typically found in slow-flowing or still waters, often with a muddy bottom and abundant aquatic plants. It is often abundant in off-channel habitats, such as backwaters and lagoons, and in deep, sheltered holes chironomids. Breeding: Females usually discharge the eggs in portions. A great part is retained and later resorbed. River Spawning occurs in spring and summer. Females produce large numbers (300,000–900,000) of small eggs (0.8–1.0 mm diameter) in 3–4 batches, at intervals of about two weeks. The eggs are adhesive and laid in shallow water, usually on weeds. Hatching occurs after 3–6 days and hatchlings are about 4–5 mm in length. The eggs are very sticky and clot together if not treated with Tannin. Stickiness is less pronounced with overripe eggs. The most favourable temperature for incubation is 25° C. Hatching takes place after 36 – 43 d° (day degrees).Tench may live for 20–30 years and reach maturity at 3–4 years.