Beneath the surface

This fundamental natural phenomenon is obviously vital for all fish but how they go about it varies from species to species

“Just before spawning the eggs may account for 25 percent of the mass of the fish”

WITH the days lengthening and water temperatures slowly creeping up, coarse fish will be gearing up for spawning in the months ahead. In our temperate climate with relatively harsh winters, coarse fish spawning generally takes place in the spring to give the larval offspring the greatest opportunity to feed and grow over the summer months. This is a critical time in the lives of fish. The strength of the year class is often governed by how well the fish grow, and subsequently survive, during this critical first 12 months. In contrast, salmon and trout spawn in the late autumn, with the eggs buried in spawning nests called redds dug into the gravel riverbed. Here the eggs hatch and the young fish remain as they slowly absorb their massive yolk sacs. This in-built food supply gives salmonids a great head start, especially in northern latitudes where the short summers give them limited time to grow and feed. In coarse fish the eggs for the year ahead start to develop in the autumn and take several months to reach maturity. During this time the eggs grow in size, but even though a fish may be carrying several hundred thousand oocytes they take up only a few percent of the fish’s mass. Just before spawning the eggs rapidly absorb water and swell in size, often leading to fish which look swollen and obviously ready to spawn. At this point the eggs may account for 25 per cent of the mass of the fish. Once the eggs have begun to swell, the female fish is unlikely to feed a great deal, because the eggs put pressure on the gut. Normally, the fish will be laying up close to the intended spawning site waiting for the perfect conditions. Male fish normally only put on a small amount of mass thanks to the development of their sperm and do not have the same swollen appearance as the females. Many male coarse fish do, however, go through some more subtle physical changes in the lead up to spawning. Often the most noticeable are the development of small white bumps on the head and along the flanks. These calcium tubercles are most common in bream, where males may be covered in them right through the year. They can also be found on many other species although to a lesser extent. Male fish also tend to develop a rough skin, less visible but obvious to the touch. The first of the coarse fish to spawn are pike and dace. This is normally undertaken in

early March, although the habitat used by the two species couldn’t be more different. Pike tend to use dense stands of plants, especially reeds, in shallow water along the edges of lakes and often in side-channels of rivers. Dace spawn in shallow gravelly runs, often in tiny streams, where eggs are laid in the gravel. By spawning so early young pike have several weeks to feed and grow on a diet primarily made up of invertebrates before other coarse fish spawn. By the time young roach, chub and bream eggs hatch the pike will already be switching to a fish diet, just as their prey become available to them. Young pike can grow very quickly on this rich diet and often measure close to six inches in length by the end of their first year. The early spawning strategy adopted by dace means that by the time other species have hatched they are already 30mm-40mm in length and feeding on much larger food items. By gaining access to different foods before other species, dace ensure that they are not competing for the same food. By May spawning is in full swing with roach and gudgeon often timing their annual mating ritual at the same time in the middle of the month. This is purely coincidental, but if you search for red exposed roots of willow trees in the margins of rivers and lakes you will often find them covered in opaque roach eggs at this time. Bream and chub spawn next, although both species can spawn several times in a warm summer. Chub in particular tend to spawn several times and often fish will still be carrying eggs into July. The final species to spawn are those that have the centre of their natural distribution in warmer climes. Tench, carp and barbel fit into this category, with spawning often taking place through June and July. The progeny of these late spawning species will often find that they only have a few weeks of abundant food and warm temperatures in which to grow. Often this growing season is too short for the fish to reach the minimum size for them to overwinter successfully and whole year classes may perish as a result. The strategies adopted at this time of the year by our coarse fish are fascinating and yet only rarely are we lucky enough to witness them. Keep your eyes and ears peeled this spring, especially very early in the morning, when most spawning activity is focussed, and you may well be lucky enough to witness this natural marvel.