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Fish

Tench

Tinca tinca

Tench

General Overview

The tench is a unique and fascinating fish in Romanian waters, immediately recognized by its characteristically stocky body, very wide at the tail region, extremely tiny scales deeply embedded in the skin, and the thick layer of mucus covering its body giving it a characteristically slippery texture. It is the "doctor fish" of freshwaters - in the past it was believed that its mucilage had healing properties and that other fish would rub against the tench to treat their wounds. In the Danube Delta, the tench is extremely common and abundant in all still or very slowly flowing waters, particularly preferring muddy waters rich in aquatic plants. Unlike most cyprinids that avoid very muddy waters, the tench thrives in these conditions due to its unique adaptations, including resistance to very low oxygen levels. An interesting aspect is that the tench has color variants - the typical wild form is dark olive-green to almost black, but in fish farms there is also a spectacular golden variant grown as an ornamental fish.

Physical Characteristics

The tench has a very characteristic and immediately recognizable body: stocky, thick, robust, strongly compressed laterally in the body region but very wide and deep in the tail region - the caudal peduncle is characteristically extremely deep and short, giving a unique silhouette. The head is small and triangular. The eyes are very small, red-orange, situated high on the head - an adaptation for benthic life. At the corners of the mouth is a single pair of short but well-developed barbels. The scales are extremely small (96-115 on the lateral line), deeply embedded in the skin, almost invisible - creating a smooth texture.

The most distinctive feature is the thick layer of mucus (mucilage) covering the entire body, with antimicrobial and antifungal properties. Coloration varies dramatically: in muddy waters - blackish-green or almost black back, dark green flanks with golden or bronze iridescence, greenish-yellow belly; in cleaner waters - greenish back, green flanks with intense golden iridescence, golden-yellow belly. The caudal fin is nearly straight or slightly rounded. Average dimensions are 25-40 cm and 500 grams-1 kg.

Habitat & Distribution

The tench is a strictly benthic fish occupying exclusively still or very slowly flowing waters with muddy bottoms and abundant vegetation - it is specialized for "heavy", muddy, warm, moderately oxygenated waters where most other species don't thrive. In the Danube Delta, the tench is ubiquitous and extremely abundant, being one of the numerically dominant species: all permanent and temporary lakes and ponds, abandoned channels, floodplains, and even very muddy and weedy areas where other fish cannot survive.

Ideal habitat includes: small to moderate depths (0.5-3 meters), exclusively muddy bottoms, extremely abundant aquatic vegetation, still or imperceptibly moving water, warm water in summer (tolerates up to 30°C), and moderate to low oxygen. The tench is very sedentary - it doesn't migrate long distances. In winter it enters a deep resting state, hiding in the deepest zones, buried in mud, reducing metabolism to a minimum.

Behavior & Feeding

The tench is an opportunistic benthic omnivore specialized in methodically rooting through the mud on the bottom. Animal food: aquatic insect larvae (especially chironomids), oligochaete worms, small mollusks, tiny crustaceans, earthworms, and other benthic invertebrates. The plant component is significant: seeds of aquatic and terrestrial plants, young buds and shoots of aquatic plants, benthic algae, plant debris, organic detritus from mud.

The feeding mode is very characteristic: the tench intensely roots the mud with its snout and mouth, aspirating sediment and selecting edible particles - leaving distinctive "holes" in the muddy bottom and creating clouds of silt. Feeding activity is intense in the early morning (5-10 AM) and evening (6-10 PM). It can survive a whole day completely out of water thanks to the thick layer of mucus that prevents dehydration of the skin and gills.

Life Cycle & Reproduction

The tench reaches sexual maturity at 2-4 years (earlier in warm southern waters), when it is 15-25 cm long. Reproduction takes place in late spring and summer, between May and August (one of the longest reproduction periods among cyprinids), when water temperature reaches and stays at 18-25°C (optimum 22-24°C). The tench stays in the same lake or pond, moving only toward shallower areas with extremely dense vegetation.

Fecundity is extraordinary: a female lays 200,000-600,000 eggs per season in 3-4 separate batches with two-week breaks between them. Eggs are extremely small (1 mm diameter), sticky, and adhere massively to aquatic plants. Embryonic development and hatching are extremely rapid: 3-4 days at 20-22°C. Growth is relatively slow: in the first year 5-10 cm, in the second 12-18 cm, in the third 20-25 cm and 250 grams.

Conservation Status

The tench is classified as "Least Concern" (LC) by IUCN, with an extremely wide distribution in Europe, Asia, and having been introduced to North America. In the Danube Delta, populations are extremely healthy, numerous, and stable, with the tench being one of the most abundant species. It benefits from minimal protection: minimum legal retention size of 25 cm, reproduction prohibition period (May-June), but no strict catch limits.

The tench plays an important ecological role: consuming benthic invertebrates and processing organic detritus in sediments, while also serving as prey for predators. Threats are minimal due to extraordinary adaptability: resistant to moderate pollution, tolerates low oxygen, thrives in degraded habitats. Main potential threats include draining of ponds and lakes for agriculture and extreme eutrophication leading to massive summer mortalities through complete anoxia.

Sources

  • Wikipedia: Tench
  • FishBase: Tinca tinca
  • Various scientific publications on tench biology in the Danube Delta