The wels catfish (Silurus glanis), also called sheatfish or just wels, is a large species of catfish native to wide areas of central, southern, and eastern Europe, in the basins of the Baltic, Black and Caspian Seas. It's a fascinating creature with a diverse diet and unique hunting strategies. Understanding the feeding habits of catfish is crucial for anglers looking to improve their catch rates and for fisheries biologists aiming to manage and conserve aquatic resources.
Physical Characteristics and Hunting Adaptations
The wels catfish has several key physical characteristics that aid in its feeding habits. The first third of its body is wide and sturdy, with a flattened head and tiny eyes. Notably, it has leathery skin (without scales) that’s equipped with chemoreceptors, which give them a heightened sense of smell when looking for food. They also have barbels resembling a cat’s whiskers around their mouths that are equipped with taste receptors. The wels catfish's mouth contains lines of numerous small teeth. It is adorned with two long barbels on the upper jaw and four shorter barbels on the lower jaw.
The wels relies largely on hearing and smell for hunting prey (owing to its sensitive Weberian apparatus and chemoreceptors). Like many other catfish, the species exhibits a tapetum lucidum, providing its eyes with a degree of sensitivity at night, when the species is most active. With its sharp pectoral fins, it creates an eddy to disorient its victim, which the predator sucks into its mouth and swallows whole. The skin is very slimy. Skin colour varies with environment; clear water will give the fish a black color, while muddy water will often tend to produce green-brown specimens. The underside is always pale yellow to white in colour. Albinistic specimens are known to exist and are caught occasionally.
Dietary Habits: An Opportunistic Carnivore
If you’re wondering what catfish eat, the answer is just about anything. These fish are opportunists that feast on a wide array of food depending on what’s available. Generally speaking, flatheads catfish are predators that like to ambush live fish. Blue and channel catfish are mostly scavengers that will also prey on other fish when given the opportunity. A catfish’s diet depends on what’s available, as well as the fish’s age and size.
Like most freshwater bottom feeders, the wels catfish lives on annelid worms, gastropods, insects, crustaceans, and fish. Larger specimens have also been observed to eat crayfish, eels, frogs, snakes, rats, voles, coypu, and aquatic birds such as ducks, even cannibalising on other catfish. It feeds relatively little, with its daily food intake representing 1 to 3% of its weight.
Read also: In-Depth Look at Flathead Catfish Food
Seasonal Variations in Diet
Seasonal changes significantly influence the feeding activity of catfish. Just like all other cold-blooded species, a catfish’s appetite will change depending on temperatures. “The warmer they are, the higher their metabolism, and the more they’re going to eat,” Smith says. As the water temperatures drop, their feeding activity tapers off as they’re unwilling to move far to chase down a meal.
A study conducted in Sıddıklı Dam Lake revealed the stomach fullness index (FI) varied significantly among the seasons, with Winter showing the highest values (0.827). On the other hand, the lowest value was detected in the Autumn season (0.480).
- Spring: The most important food item for wels catfish in Spring is T. tinca (IRI% = 67.74), followed by fish remains (IRI% = 9.9%) and C. carpio (IRI% = 7.1).
- Summer: T. tinca (IRI% = 75.84) constituted the main food item of the species. A. boyeri (IRI% = 14.3) was determined as the second important food type.
- Autumn: T. tinca (IRI% = 83.9) was determined as the most consumed food type, followed by fish remains (IRI% = 8.4) and unidentified fish (IRI% = 6.4) groups.
- Winter: T. tinca (IRI% = 63.0) constituted the main food item. Fish remains (IRI% = 15.6) were identified as the second important nutrient.
According to Schoener overlap index (Cxy) values, it was determined that the diets of wels catfish were similar in all seasons except Summer and Winter (Cxy = 0.596251).
Diet Based on Age and Size
A catfish’s diet also changes as it grows. Younger channel cats will eat a variety of plants, along with small invertebrates, insects, and mollusks. As they grow, they typically shift to a more carnivorous diet and will add more fish and crustaceans to their diet.
The Sıddıklı Dam Lake study also analyzed stomach content based on age and length. It was determined that the average stomach FI value was highest (3.8) in 1-year-old fish and lowest (0.23) in 3-year-old fish.
Read also: Catching Catfish: A Guide to Their Diet
- The main food of 1-, 2-, and 3-year-old wels catfish is A. boyeri (IRI%>75).
- The primary food of individuals aged 4, 5, 6, 7, 9, 10, and 11 years was T. tinca.
- T. tinca was consumed extensively by fish aged 4 years and above but was not consumed by individuals aged 1, 2 and 3 years.
- Depending on the increase in age, a decrease in the importance of Odonata, Bivalvia, Isopoda, Gammarus spp., dipter pupae, and dipter larvae in the diet was determined.
- It has also been determined that wels catfish feed entirely on fish and vertebrates after the age of 4.
Stomach FI also varied between length groups. It was determined that the average stomach FI was at the highest level (0.82) in small-sized (<47.1 cm) individuals, while it was at the lowest level (0.64) in medium-sized (47.1-74.0 cm) individuals.
- A. boyeri (IRI% = 73.3) constituted the most important food of small-sized wels catfish. The secondary important food type was T. Tinca with an IRI value of 15.7%.
- The main food type of wels catfish in both medium and large size groups was determined as T. Tinca.
- Benthic invertebrates were consumed mostly by small-sized wels catfish, and the type of food consumed in small-sized wels catfish was less diverse compared to other size groups.
- Food diversity in medium-sized wels catfish increased, and all fish species present in the Sıddıklı dam lake were included in the food composition.
- Common carp have never been consumed by small-sized individuals, and their importance in the diet increases as the size increases.
According to Schoener overlap index (Cxy) values, similarity was detected only in the diets of medium- and large-sized wels catfish (Cxy = 0.8534).
Hunting Strategies and Habitat
The wels catfish lives in large, warm lakes and deep, slow-flowing rivers. It prefers to remain in sheltered locations such as holes in the riverbed, sunken trees, etc. It consumes its food in the open water or in the deep, where it can be recognized by its large mouth.
Catfish are bottom dwellers, but they don’t feed on the bottom 100 percent of the time. More often than not, catfish are found on or near the bottom of waterbodies. “A lot of times at night, they’ll come up into more shallow areas more toward the surface and feed,” Jolley says.
Researchers at the University of Toulouse, France, in 2012 documented individuals of this species in an introduced environment lunging out of the water to feed on pigeons at water edge. 28% of the beaching behaviour observed and filmed in this study were successful in bird capture. Stable isotope analyses of catfish stomach contents using carbon-13 and nitrogen-15 revealed a highly variable dietary composition of terrestrial birds. The wels catfish has also been observed taking advantage of large die-offs of Asian clams to feed on the dead clams at the surface of the water during the daytime.
Read also: Healthy Catfish Recipes
Implications for Anglers
Understanding what catfish eat is about tapping into their adaptable and opportunistic feeding habits. Seasonal changes, varying aquatic environments, and available forage all play a significant role in shaping a catfish’s diet. For anglers looking to land a giant catfish, success hinges on understanding their dietary habits and mimicking what they’re inclined to eat in their habitat.
The options for catfish bait are as varied as their diets, but it’s always best to think about what the main food sources are in the water body you’re fishing. When targeting bullheads, a nightcrawler fished on the bottom is sometimes all you need. Channel cats can be caught on simple baits like white bread, cheese, or chicken gizzards, but as a rule of thumb, the smellier the bait the better. Especially in warmer water, where smells disperse more quickly.
If you’re looking to tangle with the larger catfish species, using live or cut bait is often a better way to go. Getting your baits down deep is important no matter what species you’re targeting.
Conservation and Ecological Impact
There are concerns about the ecological impact of introducing the wels catfish to regions where it is not native. Following the introduction of wels catfish, populations of other fish species have undergone steep declines. Since its introduction in the Mequinenza Reservoir in 1974, it has spread to other parts of the Ebro basin, including its tributaries, especially the Segre River. The wels catfish may have established a population in Santa Catarina, Brazil.
Understanding the feeding habits of wels catfish is essential for managing aquatic resources and developing conservation strategies. S. glanis significantly influences regional ecosystem dynamics by affecting predator-prey relationships and biological diversity. Analyzing this species' diet, habitat preferences, and reproductive strategies provides essential data for the sustainable management of water resources and the formulation of fisheries policies.