Spring spawning of freshwater fish and their unusual survival strategies

Spring fish spawning is a new beginning for many freshwater and migratory species. Giving birth to the next generation sometimes requires quite sophisticated procedures. These can include long-distance migrations from the high seas to mountain streams, wading elaborate nests or enlisting the help of an incubator. Such peculiar methods are sometimes quite sensitive to human-induced disturbances. More details can be found below!

Spring fish spawning and underwater stickleback nests

From late March to early July, sticklebacks mating. Freshwater forms mating where they used to live. Marine populations, including those in the Baltic, ascend streams and rivers flowing into the All-European Ocean. The stickleback remains a fish readily kept in coldwater aquariums for good reason. In spring, the males are not inferior in beauty to many exotic fish. With their bright orangish or red throats and the metallic flash of their entire bodies, they look impressive, despite their microscopic size.

Their construction craftsmanship is also dazzling. In holes on the bottom, not infrequently between seaweed, they wind nests of plant debris laced with the secretions of their own kidneys. Attracted to them, the females lay eggs, which the masterspour milt over asquickly as possible. Having fertilized the eggs, the father is able to chase the mother away so that she does not devour her own children. This is because it lays a record low number of eggs for a fish, a mere 60-70 eggs (not 60-70,000, as in the case of many similarly sized species). It will guard the eggs, and then the hatchlings, until the latter resorb their gall bladders and swim off towards an independent existence.

The stickleback has been called the chart, fish weed, spike or executioner for a reason. To this day it causes losses in aquaculture. It also drives other fish, more valuable for fishing or science, out of the Baltic Sea. As you can see, excellent care guarantees greater success than tremendous fecundity. Like other pests and weeds, from the rat to the radish, the stickleback has also become an important model organism for biomedical research [1, 3, 7].

Underwater incubators

Archaic are the customs of the roseate (hatchetfish), trumpeting from April to June. During this period, the female develops quite a large abalone – a tube-shaped extension of the cloaca, sometimes reaching several centimeters in length. Thanks to it, she introduces her eggs, which are quite large (for the size of spawners), into the gill cavity of the scaphopod or barkfish. Then the male injects the live clam with his sperm (milt).

The fertilized eggs, and later the hatchlings, enjoy favorable conditions in the gill cavity of their living incubator for some time. Despite such sophisticated biology, the hatchetfish has long remained common in European waters. Today it is subject to species and habitat protection. The expansion of giant Chinese rats contributes significantly to its disappearance. Not only do the rosella’s eggs languish in the cavities of these alien bivalves, but the glochidia of the Chinese rats also sensitize European carp. The hypersensitive fish then shed or otorbate the glochidia of scaphopods native to Europe, without which the mature clams will run out. Without them, they will become extinct and so will the pinks [1, 5, 7].

Paradise lost of fish and fishermen

As late as the 19th century, sea lampreys were still heading from the high seas to the mouths of Polish rivers in April. In the 20th century, they were occasionally caught in the Tyn, Elblążka and lower Vistula. Each female laid up to 300,000 grains of eggs into nests prepared in the sand. Then the spawners died. The blind larvae hatched from the eggs in June. Parpoches and allozoan finches also entered the estuarine sections of larger rivers from April to June to litter eggs. There were 140-180,000 eggs per female parpoe, and 100-200,000 eggs per female alosas [1, 2, 4, 5, 7].

In April and May there were runs of the then indistinguishable native western and Baltic sturgeon. Looking for the best spawning grounds, they forced their way much farther up the rivers than lampreys or parpohes, reaching the Narew and San rivers. Until the mid-19th century, it was in Poland that much of the famous Russian sturgeon fishing grounds were located, from where they were exported to the metropolises of Czarist Russia or to western Europe. As late as the beginning of the 20th century, several tons of these living fossils were still caught annually [2, 5, 6, 7].

Upstream of the Vistula, Oder and coastal rivers, cherts migrated in March and April to litter eggs from May to July. Until the dam in Wloclawek was built, they were caught in bulk in our country, by the dozens of tons. Their meat, tasty both fresh and canned, was highly valued. Today, the certa is a great rarity [2, 5, 7].

March or April brought the end of the hatching of young sea trout and noble salmon. Already in the 1950s and 1960s it was known that lake trout survived only in Wdzydze and its former bays in the Kashubian Lake District. However, it was assumed that the advances in breeding would not only satisfy domestic needs, but also allow the export of fry abroad and restore the population of sea trout by restoring the wandering instinct of lake trout released into the Baltic Sea and the dam reservoirs of the Subcarpathian region [3, 5, 7, 8].

Long-distance migration has proven to be the life strategy most vulnerable to human pressures, in this case the interruption of the longitudinal continuity of watercourses, combined with overfishing and pollution dumping. Biennial fish compete with amphibians to be the closest group of vertebrates to extinction and the most threatened group of freshwater species to disappear – at least at certain life stages. The live incubators of roseate were still working brilliantly in the 20th century. Only the advent of Chinese substitutes threatened our hatchetfish. The life-history strategy of sticklebacks is labor-intensive and extremely risky due to the scant number of offspring. However, under the conditions of the Anthropocene, it is proving surprisingly effective.

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, L. (2021). Angling atlas. Wyd. SBM Spzoo, Warsaw.
4. Nikolski, G. (1970). Ichthyology in detail. PWRiL Warsaw.
5. Rudnicki, A. (1968). Ryby wód polskich. PZWS, Warsaw.
6. Sandner, H., Wojcik Z. (1983). Nature’s calendar. Wiedza Powszechna, Warsaw.
7. Wziątek, B. (2023). Atlas of Polish fish. 140 species. SBM Spzoo Publishing House, Warsaw.
8. Radtke G., Dębowski P. 1996 Trout from Lake Wdzydze, Salmo trutta m. lacustris L., in the years 1951-1995. Zoologica Poloniae, 41(Supl.), 99-104.