Spring spawning of freshwater fish

April is an important month in the calendar for many fish, so also for anglers and hydrotechers. It is then that the spring spawning of many predators of our fresh waters ends, from small steelhead through medium grayling, rainbow trout and perch to large pike. It also begins the reproduction of a multitude of still-living species from the most diverse families – from cyprinids to piscivores and sticklebacks to sticklebacks.

Spring chutzpah of freshwater fish

In April, a lot happens in the erotic life of fish. Icarus are littered with roaches, dace, brook minnows, slivers, sabaneye and many others. Sticklebacks are wriggling their nests. In densely overgrown ditches and shallow, seemingly fishless ponds, our piscivores and invasive grasslings begin to breed. In the shallows of oxbow lakes, roseate can be observed using native mussels as living incubators for their fry. There are strings of mumps from late April to late May, and smelt from February to May. Also, some predators begin to chomp only after the ice is left on the largest lakes in Suwalki and the Tatra Mountains. We are talking about river lamprey, asp and zander, among others. Since March, idlers and loggerheads have been rubbing continuously.

Spring spawning of cyprinids

Forming warts on the fins and skin of male dace in March and April is not a disease! On the contrary – it is a sign that their spawning is starting. Given the size of the parents (from a dozen to twenty-something cm), the egg grains are quite large, as they reach about 2 mm in diameter. These tiny, schooling fish are found primarily in mountain streams and rivers, less often in lakes, and sometimes even in the most heavily-salted bays of the Baltic Sea. Fish farmers regard them as egg-eating pests of more valuable species. Anglers eat them rather infrequently because of their brawn, although they often use them as live bait for tastier fish [2, 3, 6].

The dace reaches considerable size. It can be as much as 0.4-0.8 m in length, and 2-5 kg in weight, while for a dace(Leuciscus) classified in the same genus, 0.3 m and 0.25 kg is already quite a lot. Weirs also usually stay in rivers, in winter looking into lakes. From April to June they ascend the watercourses. They stick their eggs to sandy or gravelly substrate, less often to seaweed. Males then exhibit a spawning rash. A color variant of the weir is the golden orpha, exhibited in garden ponds for its orange or golden-purple coloration. The meat of this fish was not valued in the past, but today we can’t grimace so much, so the importance of net fishing, not to mention angling, is growing [3, 5, 9].

Spawning of current and former piscivores

In the spring, the tiny common goats and sabaneevs (golden goats) of the piscivorous family come together to spawn, as well as the slugs, today transferred in systematics from the piscivorous to the clinging or Nemachilidae (so exotic that they lack a Polish name). Goat spawning is poral. It lasts from April to June in golden goats, and from May to July in common goats. Total fecundity depends on body weight. It ranges from 112 to nearly 4,300 egg grains in one season. Females are generally larger than males. Their reproduction tends to be intriguing, as triploid hybrids are sometimes observed, an otherwise unique phenomenon among vertebrates.

It has been heard for decades that the separate evolutionary and ecological lineages of the common goat and the even rarer golden goat should be treated as separate species. So far, nothing has come of this either for nomenclature or for species protection regulations in Poland. Specimens found in the Oder, Vistula and Dniester river basins (in the Polish part of the Strvizh) are now classified as Baltic goats, while the now-extinct herds from the Black Orava are classified as Balkan goats. Germans consider the Oder goats either Balkan or endemic Oder goats [2, 3, 6, 9].

Slightly larger than the common goat, the slime is also not a giant with its length of 15 cm at most. It is quite common in mountain streams. It is also found in the Lowlands, in rivers and lakes with fairly well-oxygenated water. The tiny grains of its eggs stick to stones, gravel or seaweed. They are laid on a hard substrate, in batches from March to May. Then the father watches over them for some time. While in the nineteenth and twentieth centuries it was considered an economically worthless species (if not harmful as a devourer of the eggs of more valuable species), and requiring clean water, today it is protected by the Habitat Directive and our Nature Conservation Act. It is also known to show some resistance to sewage inflow [3, 6, 9].

And mountain scorpen

As in the case of slivers and goats, the legal-administrative status of our mountain scorpenes: pike-finned and whitetip-finned (common). They, too, have long been regarded as prominent pests, devouring the spawn of salmonids or current carp. In April or May, male whitetipheads choose a place for the eggs between stones, while females meticulously clean them. The egg grains are quite large, considering the size of the spawners. Indeed, they reach up to 2 mm in diameter with a 10-20 cm long male. The father guards the eggs, securing a constant supply of oxygen-rich water by fanning with his fins. Incubation takes about 3 weeks [3, 5, 6, 9].

Spring spawning of predators

The asp (rapa, chwat) is in a few respects an exception among the cyprinids. One of the few true predators in a family composed almost exclusively of still-living fish, possibly herbivores such as amur and toppy. Also unique is its legal and administrative status in Poland. Although listed in the Annexes of the Habitats Directive, it has not lived to see species protection, unlike a couple of other species listed in the document, having been exterminated for centuries as a fish weed.

Fishing enthusiasts highly value it for its prowess and spectacular jumps. Rapa matures in its fourth year, at about 0.3 meters in length. Migratory ecotypes trumpet a slightly shorter time than the sedentary ones. The former from March to May, the latter until April. Eggs are laid on rocks, less often tree roots or seaweed, in sections of rivers with swift currents and hard bottoms, with water temperatures of 5-14°C. After an incubation period of nearly half a month, about 7-millimeter fry hatch. Over the next week, the tiny asps will pump their swim bladders. Although the boa constrictors are dissimilar in appearance and behavior to ides, they sometimes interbreed with them [3].

The steelhead is a rare case of a salmonid species, spawning in spring rather than in autumn or early winter. Its mating habits are somewhat reminiscent of the behavior of Pacific salmon, as a spawning hook is formed in males – the mandible takes on a hooked shape, enlarges and colors. Males mature 4-5 years after hatching, females about a year earlier. Looking for optimal spawning grounds, they ascend rivers. There, on gravelly or rocky shallows, the females dig holes for eggs with strokes of their tails. For every kilogram of their body weight, there are about 1,000 orange egg grains about 4-6 mm in diameter.

Such a late spawning season, for a representative of the salmonids proper, makes incubation shorter than in their cousins: trout and sea trout. Less than 40 days after spawning (with the warmth of the stream water at 7-9°C), the larvae hatch. In Poland, this is late May and early June. In half a month, the hatchling depletes the yolk sac reserves and begins a predatory lifestyle. At first it attacks invertebrates, then switches to small, current-smoking fish. Cephalopods have lost their natural refuges in Poland (tributaries of the Danube), but have been successfully introduced into the streams of the Sudeten and Carpathian basins of the Oder and Vistula. Former ichthyologists saw success here comparable to the restoration of the bison in the Bialowieza Forest [3, 9].

Sandpiper is a sizable predator from the perch family, active mainly at night. It prefers deep, naturally turbid, well-oxygenated waters. Besides, it is not very picky in terms of chemistry and strength of current, so we will meet it both in lakes and dammed reservoirs, as well as flooded pits, medium and large rivers and coastal shallows of the Baltic Sea.

It usually thaws at a depth of nearly 1 m, among submerged branches and roots, at a temperature of 12°C. The men build primitive nests there, into which the ladies lay 200-300 thousand sticky, light-gold eggs, 0.8-1.5 mm in diameter. The father guards the eggs and secures a constant supply of the cleanest, oxygen-rich water possible. The incubation rate of small pikas depends on the temperature, for 10 ° C it will be about 12 days, for 20 ° C it will be a mere 3 days. The hatchlings, as befits the children of darkness, feeding at night, cannot tolerate strong light. It can even kill them [3, 9].

April is a time of intensification in the life of our freshwater fish. The spawning of a few tuvad species, including grayling, perch and pike, takes place. Many species from a variety of families, often leading different lifestyles, come to spawn, securing (or not) eggs and fry in different ways. Surveillance of our waters, especially spawning grounds, must also be stepped up so that there are no such mishaps as in Uniesta this season.

MAIN PHOTO: Kelly / pexels

In the article I used, among others:

1. Heese, T., Przybyszewski, C. (1993). The life of fish. Wyd. Uczelniane Wyższej Szkoły Inżynierskiej, Koszalin.
2. Holcik, J., Mihalik, J., Maly, J. (1971). Freshwater fishes. PWRiL, Warsaw.
3. Kolasa, Ł. (2021). Angling atlas. Wyd. SBM Spzoo, Warsaw.
4. Kostrzewa, J., Grabowski, M., Zięba, G. (2004). New invasive fish species in Polish waters. Archives of Polish Fisheries 12 (suppl. 2): 21-34.
5. Nikolski, G. (1970). Ichthyology in detail. PWRiL Warsaw.
6. Rudnicki, A. (1968). Ryby wód polskich. PZWS, Warsaw.
7. Sandner, H., Wojcik Z. (1983). Nature’s calendar. Wiedza Powszechna, Warsaw.
8. Trembaczowski, A. (1989). Night fishing. PWRiL, Warsaw.
9. Wziątek, B. (2023). A tlas of polish fish. 140 species . Published by SBM Spzoo, Warsaw