Tench
Specie Description

The Tench, scientifically classified as Tinca tinca, is the sole species in the genus Tinca, making it taxonomically unique among European cyprinids. The common name "tench" derives from the Old French word "tenche," which itself originates from the Late Latin "tinca." This fish has been known by this name for centuries across Europe, with remarkably consistent nomenclature across different languages - "Tanche" in French, "Schleie" in German, and "Tinca" in Italian and Spanish.

In English-speaking countries, the tench is sometimes affectionately called the "doctor fish," stemming from medieval folklore that claimed other fish would rub against tench to heal wounds, supposedly due to the tench's exceptionally thick protective mucus layer. While this healing ability is mythical, the nickname has persisted and reflects the fish's reputation for hardiness and disease resistance. The species is also occasionally referred to as the "mud fish" due to its preference for soft, muddy substrates.

Within the aquarium and pond hobby, several color varieties have been developed through selective breeding. The most common is the wild-type green tench, exhibiting the natural olive-green to bronze coloration. However, the golden tench, a xanthic color morph displaying brilliant golden-yellow coloring, has become increasingly popular among ornamental fish keepers since its development in the early 20th century. This variety maintains all the hardy characteristics of the wild type while offering striking visual appeal. Some sources distinguish between "lake tench" and "river tench," though these represent ecological variations rather than taxonomic subspecies, with river specimens typically being more streamlined and active than their deeper-bodied pond-dwelling counterparts.

The Tench is a stocky, heavy-bodied cyprinid with a distinctive appearance that makes it easily recognizable. Wild-type specimens display a dark olive-green to bronze coloration on their dorsal surface, gradually transitioning to a yellowish or creamy underbelly. The scales are extremely small and deeply embedded in the skin, covered by a remarkably thick layer of protective slime that gives the fish a velvety appearance and slippery texture. This mucus coating serves as an important first line of defense against parasites and injuries.

Adult tench typically reach lengths of 12 to 20 inches in pond environments, though specimens in large natural lakes can grow substantially larger, occasionally exceeding 24 inches and weights of 15 pounds or more. The body shape is robust and laterally compressed, with a relatively high back and a small, terminal mouth surrounded by two short barbels at the corners. These barbels are sensory organs that help the tench locate food in murky water or when foraging through substrate at night.

The fins of the tench are notably rounded and thick, particularly the caudal fin, which is square-edged rather than forked - an unusual characteristic among cyprinids. The dorsal fin is set relatively far back on the body and is short with smooth rays. All fins share the same dark coloration as the body, ranging from olive-brown to gray-green. The pelvic fins in males are noticeably larger and more muscular than in females, which becomes particularly apparent during the breeding season.

Sexual dimorphism in tench becomes evident upon close examination. Males develop enlarged, thickened pelvic fins with a distinctly muscular second ray, which they use during spawning to maintain contact with females. Males also tend to be more streamlined with a slimmer profile, while females become noticeably fuller and rounder when gravid with eggs. During breeding season, males may develop small white tubercles on their heads and pectoral fins, though these are less prominent than in many other cyprinid species.

The golden tench variety presents a stunning alternative to the wild type, displaying uniform golden-yellow to orange coloration across the entire body. These fish retain the same body shape, scale structure, and thick mucus coating but lack the dark pigmentation of their wild cousins. Golden tench maintain all the hardiness and characteristics of the species while offering exceptional visibility in ponds. Some breeders have also developed partially colored variants showing mottled patterns of gold and green, though pure golden specimens remain most popular in the ornamental fish trade.

The Tench is native to a vast geographical range spanning from Western Europe across to Asia, including the British Isles, continental Europe, and extending eastward through Siberia to the Lena River basin. The species has been widely introduced beyond its natural range and is now established in North America, southern Africa, Australia, and New Zealand, though it is sometimes considered invasive in these regions due to its ability to thrive in various conditions and compete with native species.

In its natural environment, the tench strongly prefers still or slow-moving waters with soft, muddy bottoms rich in organic material. It inhabits lakes, ponds, reservoirs, backwaters of rivers, and sluggish streams where vegetation is abundant and water flow is minimal. The species shows a particular affinity for waters with dense aquatic plant growth, especially areas with submerged vegetation and overhanging bankside plants that provide shelter and breeding substrate. Tench are notably absent from fast-flowing rivers and clear, cold mountain streams, preferring warmer lowland waters.

The substrate preference of tench is highly specific - they favor soft mud or fine silt where they can root and forage for invertebrates, insect larvae, mollusks, and plant material. They spend much of their time with their heads tilted downward, probing the bottom with their sensitive barbels. In natural lakes and ponds, tench typically inhabit depths of 6 to 15 feet, though they venture into shallower vegetated margins during warm weather and spawning periods. They avoid the deepest parts of lakes and rarely venture into open water far from the security of the bottom or aquatic vegetation.

Wild tench demonstrate remarkable adaptation to challenging environmental conditions. They can survive in waters with very low dissolved oxygen levels that would prove fatal to most other fish species, a trait that allows them to thrive in heavily vegetated, shallow ponds where oxygen depletion occurs during warm summer nights. During winter in temperate regions, tench become largely dormant, burying themselves in bottom mud and significantly reducing their metabolic rate. This torpid state allows them to survive frozen ponds and prolonged cold periods with minimal food intake.

Seasonally, tench behavior and habitat use varies considerably. During spring and early summer, as water temperatures rise above 64°F, tench become more active and move into shallow, vegetated areas for spawning. They aggregate in small groups around suitable spawning sites with dense aquatic plants. Summer finds them actively foraging in margins and mid-depth areas, particularly during dawn and dusk. Autumn brings increased feeding as they prepare for winter dormancy, and when winter arrives and water temperatures drop below 50°F, they retreat to deeper areas or partially bury themselves in substrate, becoming almost completely inactive until spring warming triggers renewed activity. Conservation status for tench across most of their range remains stable, and they are not considered threatened, though local populations have declined in some areas due to habitat loss and water pollution.

The Tench possesses one of the most peaceful and docile temperaments among all freshwater fish species, making it an ideal inhabitant for community ponds and large aquariums housing multiple species. These fish are completely non-aggressive and pose no threat whatsoever to other fish, regardless of size. They lack territorial instincts and do not establish or defend feeding or breeding territories, even during spawning season when many fish species become aggressive. This gentle nature extends to their interactions with their own species as well, with tench showing no hierarchical aggression or dominance behaviors.

As primarily nocturnal or crepuscular feeders, tench are most active during dawn and dusk hours, with peak foraging activity occurring in low-light conditions. During bright daylight, especially in clear water or exposed ponds, they tend to be shy and retiring, often resting in vegetated areas or partially concealed in substrate. However, in well-established ponds where they feel secure, or in ponds with surface cover from floating plants or overhanging vegetation, tench become bolder and may forage throughout the day. They learn to associate human presence with feeding time and can become quite tame, eventually accepting food directly from their keeper's hand.

The activity level of tench is best described as deliberate and unhurried. Unlike many active cyprinids, tench are not constant swimmers. They spend considerable time resting on the bottom or hovering just above the substrate, moving slowly and methodically as they search for food. Their swimming style is characterized by gentle, undulating movements rather than rapid bursts of speed. When startled, they can move surprisingly quickly but generally prefer to sink to the bottom and remain motionless rather than fleeing. This sedentary nature means they do not compete well with more aggressive or faster-moving fish at feeding time, though their excellent foraging abilities allow them to find food that other species miss.

Socially, tench are neither truly schooling fish nor strictly solitary creatures. In the wild, they form loose aggregations rather than tight schools, with multiple individuals occupying the same general area while maintaining individual space. In captivity, keeping tench in groups of three or more is recommended, as they appear more confident and display more natural behaviors when conspecifics are present. However, unlike many cyprinids that become stressed when kept alone, a single tench can thrive if provided with adequate space and appropriate pond mates. They show no aggressive behavior toward each other even in limited space, though crowding should be avoided as it increases stress and reduces water quality.

Interaction with other species is universally peaceful. Tench completely ignore smaller fish, making them safe even in ponds with juvenile goldfish or young koi. They do not compete aggressively for food, instead patiently waiting their turn or foraging for overlooked items after more aggressive feeders have finished. Their bottom-dwelling habits mean they occupy a different ecological niche than surface or mid-water feeders, further reducing competition. The thick mucus coating and relatively large size protect adult tench from harassment by other species. Young tench may occasionally fall prey to large predatory fish, but adults are essentially immune to aggression from typical pond companions like goldfish and koi, which view them as simply too large and uninteresting to bother.

Housing tench properly requires substantial space and careful consideration of their specific needs as large, bottom-dwelling cyprinids. While young tench of 4-6 inches can temporarily be maintained in very large aquariums of 180 gallons or more, these fish are truly pond species that reach their full potential only when provided with outdoor pond environments. As they mature and reach their adult size of 12-24 inches, the minimum recommended pond size for a small group of tench is 1,000 gallons, with larger ponds of 2,000 gallons or more being ideal for allowing natural behaviors and healthy growth.

The pond depth is particularly important for tench, especially in temperate climates where they will overwinter outdoors. A minimum depth of 3-4 feet is required, with at least a portion of the pond reaching 5-6 feet deep to provide adequate protection from freezing and temperature extremes. This deeper zone allows tench to retreat to stable temperatures during both summer heat and winter cold. The pond should have gradual sloping sides rather than vertical walls, providing tench with access to different depth zones and allowing easier entry and exit from the water for maintenance purposes.

Substrate selection is crucial for tench welfare, as these fish spend most of their time in contact with the bottom and actively forage by sifting through substrate. A layer of fine sand or soft mud, 3-5 inches deep, is ideal and most closely mimics their natural habitat. Alternatively, small, smooth pebbles can be used, though sand is preferable. Avoid sharp gravel or rough substrates that could damage their delicate barbels or the protective slime coating. The substrate should be sloped to create deeper areas and shallows, and should be free of debris or sharp objects. Some pond keepers successfully maintain tench without substrate, particularly in indoor systems, but this is less than ideal and may cause stress or abrasion injuries over time.

Filtration requirements for tench are moderate compared to messy species like koi, but adequate biological filtration is still essential for maintaining water quality in any pond. A combination of mechanical and biological filtration handles waste products efficiently. For a 1,000-gallon pond, a filter rated for at least 1,500 gallons provides adequate turnover and biological capacity. Since tench tolerate low oxygen levels better than most fish, aeration is less critical than for species like koi, but it remains beneficial for overall pond health and water quality. A modest air pump with air stones or a fountain providing gentle surface agitation is sufficient.

Planting the pond heavily with aquatic vegetation provides numerous benefits for tench. Submerged plants like hornwort, elodea, and water milfoil offer shelter and contribute to water quality. Marginal plants including cattails, iris, and water mint provide cover along edges where tench often forage. Floating plants such as water lilies and water lettuce create shaded areas and help control algae by competing for nutrients. The presence of plants also provides spawning substrate for breeding tench and refuge for fry. However, avoid extremely dense vegetation that could create oxygen depletion during warm summer nights.

Decorations and structure within the pond should include some larger rocks, driftwood, or artificial caves creating hiding spots and visual barriers. Tench appreciate having secure retreats, especially during their first weeks in a new pond when they tend to be nervous. However, avoid cluttering the pond excessively, as tench need open areas for swimming and foraging. A balance between open space and structured areas works best.

Equipment needs for a tench pond are relatively minimal. Beyond filtration and possibly aeration, a pond heater is unnecessary as tench are cold-water species that thrive at temperatures from 50-77°F and can survive freezing conditions. A pond thermometer allows monitoring of seasonal temperature changes. A net large enough to cover significant portions of the pond surface helps with occasional fish handling and protects against predatory birds like herons. In regions with harsh winters, a pond deicer prevents complete surface freezing and allows gas exchange. Lighting is not essential for the fish but can be used for aesthetic purposes and to allow evening viewing, though bright lights may discourage tench from emerging from cover during their active periods at dusk.

One of the tench's greatest attributes as a pond fish is its exceptional tolerance of a wide range of water parameters, far exceeding the adaptability of most ornamental fish species. This hardiness stems from their evolution in European lowland waters that experience significant seasonal variations in temperature, oxygen levels, and water chemistry. Understanding their tolerance ranges while maintaining optimal conditions ensures healthy, long-lived tench that display their best colors and most natural behaviors.

Temperature tolerance in tench is truly remarkable, spanning from just above freezing to approximately 77°F. In temperate climates, outdoor ponds naturally cycle through these extremes, and tench adapt readily. The optimal temperature range for active feeding, growth, and breeding is 64-72°F, when tench are most active and display their best colors. As temperatures drop below 55°F in autumn, their metabolism slows and activity decreases. Below 50°F, they enter a semi-dormant state, settling to the bottom and barely moving. This cold tolerance allows them to survive frozen ponds by partially burying themselves in bottom substrate where temperatures remain stable around 39-40°F. Conversely, they tolerate summer temperatures up to 77°F, though prolonged exposure to temperatures above 75°F can stress them and increase oxygen demands. Rapid temperature fluctuations should be avoided, particularly changes exceeding 5 degrees in a short period, though tench handle gradual seasonal transitions without issue.

pH tolerance is equally impressive, with tench thriving in water ranging from slightly acidic to moderately alkaline conditions. The acceptable pH range is 6.5 to 8.0, with an optimal range of 7.0 to 7.5. Unlike many sensitive aquarium species, tench tolerate pH fluctuations quite well and rarely show stress from values within this broad range. They adapt successfully to both soft and hard water conditions, making them suitable for a variety of geographical regions with different natural water chemistry. Most municipal water supplies fall within acceptable parameters for tench without requiring significant adjustment.

Water hardness, measured as general hardness (GH) and carbonate hardness (KH), shows similar flexibility in tench care. They thrive in both soft water with GH values as low as 5 dGH and hard water exceeding 20 dGH. Moderate hardness between 8-15 dGH is ideal, but this is not critical for their health. KH values should be maintained above 4 dKH to provide pH buffering capacity and prevent sudden pH crashes, particularly in planted ponds where photosynthesis and respiration cycles can affect water chemistry.

Dissolved oxygen requirements for tench are notably lower than for many other fish species, thanks to their adaptation to stagnant or sluggish waters in nature. While they certainly benefit from well-oxygenated water with levels above 6 mg/L, they can survive in conditions as low as 2-3 mg/L that would prove fatal to koi, goldfish, or most tropical species. This tolerance for low oxygen makes them particularly suited to heavily planted ponds or shallow waters that experience oxygen depletion during warm summer nights. However, consistently low oxygen levels can stress even tench over time, so maintaining adequate aeration or water movement is still recommended.

Ammonia and nitrite toxicity affects tench as it does all fish, though they show somewhat greater tolerance than sensitive species. Ammonia and nitrite should always be maintained at 0 ppm through adequate biological filtration and appropriate stocking levels. Tench can survive brief exposure to low levels of these compounds but will be stressed and at increased disease risk. Nitrate, the end product of the nitrogen cycle, is tolerated up to 40-50 ppm, though levels below 20 ppm are preferred. Higher nitrate levels can contribute to algae blooms and may affect long-term health.

Water changes in tench ponds can be less frequent than for many species due to their waste tolerance and the typically larger water volumes in ponds versus aquariums. In properly balanced, planted ponds with adequate filtration, water changes of 10-20% monthly may suffice, supplemented by topping off evaporation losses. In smaller systems or heavily stocked ponds, weekly changes of 20-25% better maintain water quality. During winter dormancy, water changes can be reduced or eliminated entirely unless water quality issues develop. Before spring, a larger water change of 25-30% helps refresh the pond as temperatures rise and tench resume activity.

Acclimation procedures when introducing new tench should account for potential differences in water chemistry between holding facilities and destination ponds. Float bags for 15-20 minutes to equalize temperature, then gradually add pond water to the bag over 30-45 minutes before releasing fish. While tench tolerate parameter differences better than delicate species, proper acclimation reduces stress and the risk of shock. Seasonal adjustments to water quality management include reduced maintenance in winter when fish are inactive, vigilance regarding oxygen levels during hot summer weather, and monitoring for ammonia spikes during spring as biological filtration reactivates and fish resume feeding after dormancy.

Tench are among the hardiest of all ornamental freshwater fish, possessing exceptional disease resistance and an ability to survive conditions that would prove fatal to most other aquarium or pond species.

Their longevity and disease resistance make them among the most reliable and low-maintenance of all large pond fish species.

Tench are opportunistic omnivores with a natural diet that reflects their bottom-dwelling lifestyle and adaptability to various food sources. In their wild habitat, they consume a diverse menu including aquatic insect larvae, worms, mollusks, crustaceans, algae, plant matter, and detritus. They are efficient foragers that use their sensitive barbels to locate food items buried in substrate, particularly in murky water or during low-light conditions when visual hunting is less effective. Understanding their natural feeding behaviors helps provide optimal nutrition in captivity.

In pond environments, tench readily adapt to commercial fish foods designed for bottom feeders. High-quality sinking pellets formulated for pond fish provide an excellent nutritional foundation and should comprise the majority of their diet. Choose pellets sized appropriately for the fish - smaller 3-4mm pellets for young tench, larger 6-8mm pellets for adults. Many pond keepers successfully use koi pellets or specialized bottom-feeder formulations. Look for foods with balanced nutrition including quality protein sources, essential fatty acids, vitamins, and minerals. A protein content of 30-40% suits adult tench well, while growing juveniles benefit from slightly higher protein levels up to 45%.

Supplementing commercial pellets with natural foods enhances nutrition and provides enrichment. Earthworms are an exceptional food source that tench consume with great enthusiasm - many pond keepers breed red wigglers or nightcrawlers specifically for feeding. Bloodworms, either live or frozen, make excellent treats and closely mimic natural prey items. Tubifex worms, while relished by tench, should be sourced carefully as they can harbor parasites if obtained from contaminated waters. Aquatic snails, whether intentionally added or naturally occurring in ponds, provide calcium and minerals. During warmer months, live daphnia or mosquito larvae offer variety and hunting opportunities.

Vegetable matter should comprise a modest portion of the tench diet. They naturally consume algae and soft plant material, particularly in late summer and autumn. Blanched vegetables including lettuce, spinach, zucchini, and peas can be offered weekly. Remove any uneaten vegetable matter within 24 hours to prevent water quality deterioration. Some tench develop preferences for certain vegetables over others. Small amounts of fruit such as melon or cucumber can be offered occasionally as treats, though these should not be dietary staples.

Feeding frequency and portion size should account for seasonal variations in tench metabolism and activity. During the active season from late spring through early autumn, when water temperatures remain above 60°F, feed adult tench once or twice daily, providing only what they can consume within 20-30 minutes. Since tench are slow, methodical feeders, allow adequate time before assuming they have finished. Multiple smaller feedings suit their natural foraging behavior better than single large meals. As autumn temperatures decline and fish activity decreases, reduce feeding frequency to every other day or 2-3 times weekly. When water temperatures drop below 50°F, stop feeding entirely as their digestive systems essentially shut down during winter torpor. Resume feeding only when spring temperatures consistently exceed 50°F and tench show renewed activity.

Delivering food effectively to bottom-feeding tench requires some consideration, particularly in ponds with mixed species. Since tench feed primarily from the substrate rather than the surface, sinking pellets are essential - floating foods will be consumed by surface feeders before reaching the bottom. Feed in areas of the pond where tench typically forage, often along planted margins or in deeper zones. Evening feeding aligns well with their crepuscular nature and reduces competition from diurnal species like goldfish and koi. Some pond keepers use feeding rings or specific feeding stations to train fish to feed in designated areas, which helps monitor consumption and prevents waste accumulation across the entire pond bottom.

Signs of proper nutrition in tench include steady growth in juveniles, maintenance of body weight in adults, bright eyes, and a healthy, thick slime coat. Well-fed tench should have a gently rounded body profile rather than appearing thin or emaciated, though they should not be obese with excessive body depth. Overfeeding manifests as water quality problems, excessive waste production, algae blooms, and potentially fatty liver disease. Underfeeding results in weight loss, lethargy, increased susceptibility to disease, and in extreme cases, cannibalism of small pond mates. Adjust feeding amounts based on fish condition, water temperature, and activity levels rather than following rigid feeding schedules.

The peaceful, bottom-dwelling nature of tench makes them exceptionally compatible with a wide variety of pond fish species, allowing creative and diverse community pond designs. Their complete lack of aggression and occupation of a bottom-dwelling niche separate from most common pond fish means they rarely compete for resources or living space. Ideal tank mates include virtually all temperate pond species that tolerate similar water conditions and do not display extreme aggression.

Goldfish in all varieties make excellent companions for tench. Common goldfish, comets, shubunkins, and fancy varieties all coexist peacefully with tench without competition or conflict. The active, surface-oriented goldfish occupy different water zones than substrate-dwelling tench, minimizing interaction. Koi are equally compatible, though the dramatically different adult sizes should be considered - large koi can reach 24-36 inches while tench typically max out around 20 inches. Ensure pond size accommodates the combined bioload and swimming space requirements of both species. Orfe (Leuciscus idus), another peaceful European cyprinid, are compatible with tench and occupy the mid-water column, creating a complete vertical distribution of species.

Other suitable pond mates include weather loach (Misgurnus anguillicaudatus), which share similar bottom-dwelling habits and peaceful temperaments. Rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) coexist well when available. In very large ponds, sturgeon species can be compatible with tench, though sturgeon require exceptional water quality and considerable space. Avoid housing tench with large predatory species like pike or bass that might attempt to prey on smaller tench, though adult tench are generally too large to be threatened by typical pond fish.

Incompatible species are few given tench's peaceful nature. Highly aggressive cichlids or territorial fish could potentially harass tench, though such species are rarely kept in temperate ponds. Very small fish like young fry or tiny nano species might be accidentally consumed by large tench foraging in substrate, though this is uncommon. The primary consideration is ensuring all species share similar temperature and water quality requirements rather than behavioral incompatibilities.

Breeding tench in ponds occurs naturally when conditions align properly, though successfully raising significant numbers of fry to maturity requires planning and sometimes intervention. Sexual maturity typically arrives at 2-3 years of age when fish reach approximately 8-10 inches in length. Sex identification becomes possible as fish mature - males develop noticeably enlarged, muscular pelvic fins with a thickened second ray, while females remain fuller-bodied with smaller, more delicate pelvic fins. Males may also display small tubercles on their heads during breeding season.

Spawning occurs naturally in late spring or early summer when water temperatures rise above 64°F and remain stable. Temperature is the primary trigger, though increasing day length and the presence of suitable spawning substrate also influence breeding behavior. Tench require aquatic vegetation for spawning, with submerged plants like elodea, milfoil, or planted basket containing fibrous roots serving as egg-laying sites. Male tench become more active and colorful during this period, pursuing females with gentle nudging and swimming alongside them.

The spawning act itself occurs during dawn hours, with pairs or small groups congregating around vegetated areas. The female releases sticky eggs in batches that adhere to plant material, while males simultaneously release milt to fertilize them. A large female may produce 300,000 to 400,000 eggs over several spawning sessions across a few days. The eggs are small, approximately 1mm in diameter, and greenish in color, making them nearly invisible among vegetation. After spawning concludes, adults show no parental care and may actually consume eggs if encountered while foraging, though the sheer number of eggs and their concealment in vegetation ensures some survive.

Eggs hatch in 3-6 days depending on water temperature, with warmer water accelerating development. Newly hatched fry are tiny, measuring only 3-4mm, and remain attached to vegetation via an adhesive organ for 2-3 days while absorbing their yolk sacs. Once free-swimming, they require microscopic foods including infusoria, green water rich in algae, and later newly-hatched brine shrimp. Natural ponds with established algae growth and microorganism populations support better fry survival than sterile systems.

Raising tench fry to maturity in the same pond as adults rarely succeeds due to predation from adult fish, including the parent tench themselves. For serious breeding efforts, separate rearing ponds or large tubs allow isolation of fry until they reach 2-3 inches, at which point they become too large for adults to consume. Alternatively, heavily planted ponds with extensive shallow margin areas provide refuge where some fry naturally survive despite adult presence. Growth rates vary based on temperature, food availability, and genetics, but young tench typically reach 3-4 inches by their first autumn, 6-8 inches by their second year, and breeding size by their third year.