Strikingly beautiful, the perch is one of the most popular of freshwater fishes among anglers. Though lacking the bold aggressiveness of pike, the perch is a worthy adversary.
The perch is perhaps one of the most popular freshwater species in the British Isles, especially with the young angler. The reason for this is that perch are voracious eaters and will willingly take bait, especially worms, placed quietly under their noses. For the young angler the capture of two or three perch, even if they are only 6in long, can enliven an otherwise fishless day. Though perch of this size are rarely of interest to the experienced angler, to the novice they offer good sport and the opportunity to develop a wide range of angling skills.
The boldness of the perch, Perca fluviatilis, is matched by its bold ap-pearance. No other species of British freshwater fish has such characteristic colouring – dark greenish brown above olive green below, and a series of vertical dark bars down the sides. The pelvic, anal and lower tail fins are orange red, the two dorsals and the upper part of the tail fin are a darker greenish brown, except for the spiny dorsal fin, which has a black blotch near its rear end. The basic coloration is, however, very variable – some perch are almost blue on the back and sides, others may be light brown.
Undoubtedly, this colouring varies with the habitat, but it also changes with the responses of the fish – an aggressive perch, faced with another of the same size, will become darker, the bars turning almost black, and the dorsal fin spot showing jet black and conspicuous on the elevated fin. This fin spot probably acts as a false eye so that, seen from the side, it may suggest to a competitor, or predator, that the fish in front is much larger than in reality. The function of the spot, however, seems never to have attracted the attention of students of fish behaviour.
The other major feature of the perch is its spines. The first dorsal fin has 13-16 strong spines, the second dorsal, the anal, and the pelvic fins, one or two each. A flattened, but stout spine on each gill cover supplements these spines, and even the scales have numerous short spikes on their free edges, giving the perch its characteristic rough feel. It is worth pointing out the falsity of the belief, held even by experienced anglers, that perch spines are venomous. Certainly, their spiny fins can give a nasty jab if handled carelessly, but it is a clean wound. Any subsequent infection is probably caused more by a soiled handkerchief wrapped round the hand than by the fish.
The ruffe, Gymnocephalus cernuus, also known as one time as the pope, is less distinctive, but nevertheless easy enough to identify in British waters. It too has a high and spiny first dorsal fin, but this is joined to the second dorsal, not separate as in the perch. Again, the pelvic and anal fins have spines, as have the gill covers, but the spines tend to be more slender than in the perch. A very distinctive feature of the ruffe is the large cavities underlying the skin on the lower side of the head. These are specially developed sensory canals, forming part of the lateral line system. The coloration of the ruffe is much less striking than that of the perch, being basically olive above, yellowish on the sides and fins, with liberally scattered dark spots and blotches.
While the perch is widely distributed throughout the whole of the British Isles – although less widespread in Scotland – its presence in the North and West is in large part due to its being introduced there for purposes of angling or food, or out of sheer curiosity. The ruffe, on the other hand, has not attracted such interest.
Its spread throughout the country is thought to be due to accidental or natural restocking processes, involving transfer with other species during restocking, or the carrying of eggs by waterfowl. Both fish are members of the family Percidae, to which the zander also belongs.
Perch form shoals of variable size throughout their lives. From the middle of their larval development, when about 10-20mm long, they form small shoals and swim actively, if slowly, both horizontally and vertically, in pursuit of rotifers and copepod crustaceans. The shoal keeps together by visual contact, and so at night it breaks up and the larvae sink singly to the bottom. At a length of 20-30mm they are found in depths of about 5ft.
The perch’s diet
For the perch of up to 5cm, small planktonic animals, chiefly crustaceans and midge larvae, are the main food, and continue to be, with the addition of fresh-water shrimps, un-156
til the fish reaches a length of 10cm. At about this length, fish become in-creasingly important as food, most of the actively swimming carp-like fishes, and ruffe and younger perch, figuring in the diet. However, this dietary graduation from invertebrates to fish varies greatly from one water to another and may de-pend very considerably on the fauna there. Research on the perch population of a Norwegian lake showed that they were still eating bottom-living invertebrates at a length of 30cm, but that there were relatively few prey fish, other than perch, available for consumption.
Competition with the zander
The tendency to cannibalism in perch over 15cm is very marked, and must have considerable bearing on the age structure of lake populations. Interestingly, zander are also highly cannibalistic in years when there are many young zander around, and studies of the biology of the two species in the Netherlands have shown that in their first year both prey on the same food. Competition for food does not seriously affect their growth in the large waters studied, but in more restricted areas it may be severe. It is certainly a factor to bear in mind in England, following the ill-judged introduction of the zander.
Both the perch and the zander, even in the earliest stages, feed by selecting by eye each item of food before snapping it up. Ruffe, in contrast, tend to live near the bottom, favouring murky or clouded water, and rely very little on sight to find their food. The elaboration of the lateral line canals on the underside of the head must be seen as a result of evolutionary processes in this kind of environment. The ruffe’s diet consists of small animals, chiefly crustaceans, bloodworms, worms, and amphipods (fresh-water shrimps), most of which are bottom-living organisms detected by vibrations through the sensory canals. The diet remains virtually unchanged for life, the ruffe never becoming a fish-eater. The ruffe is also sensitive to noise and other vibrations, and young fish have proved very difficult to keep in captivity.
Spawning in perch takes place from April to May in Britain, but the farther north the later it occurs. The extremes for the species throughout its geographical range are February and July. Although it may seem that temperature is the factor that triggers off the process, the local time of spawning must be a result of natural selection to ensure that breeding produces post-larvae and fry at a time when food for them is in good supply.
The species’ spawning habits Generally, spawning takes place in warm shallows with dense vegetation, or among underwater tree roots or the twigs and branches of fallen trees. The perch is not fussy about the place in which it spawns, and in the absence of such plants or twigs, may shed its eggs on rough rocky or stony shores in, for example, upland lakes. Usually, each female is accompanied by several males, which shed milt close to her vent as the egg strand is extruded. Spawning is a slow process, the female winding her way between the plants, roots, or twigs, and leaving on them a lacy, intertwined mass of eggs. In captivity, the female has been seen to defend the egg mass, but such behaviour has not been observed in the wild.
The number of eggs produced, all shed at a single spawning, varies strikingly between localities, and to some extent with the size of the female fish, the extremes being 950 and 210,000. The eggs hatch in 2-3 weeks, depending on temperature, and the success rate is-usually high.
Growth depends very largely on the food available, which is mainly a function of the richness of the habitat. In lakes where food is plentiful the average length has been recorded at 8-10cm at one year, 16-19cm at two years, 20-24cm at three years, 22-26cm at four years, 27-29cm at five years and about 31cm at six years. Poor growth lakes, such as Dubh Lochan in Scotland, gave mean total lengths for the first five years of 5, 8, 9, 11 and 12cm.
In fast growth lakes, some of the male fish are sexually mature at- the end of their first year and take part in spawning. The majority of males are sexually mature at two years – at a length of around 15cm – while most females mature at three years and a mean length of 20cm. Males live for 6-7 years, but females survive, continuing to grow slowly, for up to 10 years. It is virtually certain that large specimens will be females from productive waters with fast growth rates.
The perch is well-known for its tendency to overrun a lake with fish all about the same size. This phenomenon has been studied intensively in Lake Windermere, for which records go back to 1941. Many lakes contain stunted populations of perch of similar size and age. The generally accepted explanation for this is that the weather, especially in spring and summer, affects the survival of the post-larvae and fry. Years with particularly high survival rates are warm and sunny. In the case of Windermere, this has been expressed numerically as the total number of degrees that the daily surface water temperature exceeds 14°C (57.2°F) so that, for example, 10 days at 19°C (66.2°F) gives a total of 50 day degrees. When the index is above 400, a good survival rate will be ensured; if it is below 150, survival is poor.
The factors causing these differences are indirect, but are certainly connected with the availability of the right type of food as the young perch develop. Good years result in an abundance of young perch. In the absence of a large stock of bigger perch, they will continue to thrive, but by the time the next year’s young are active they will have reached a size to turn cannibal and many, if not most, of these young will be eaten. The survivors of a good year class, therefore, tend to dominate the fish – especially perch – population of a water until their numbers decline and they cease to be significant predators. The stage is then set for another year class to dominate the water.
It should be added, however, that reports of this year class dominance have been most notable in lakes in the North and West of the British Isles, where the species is not indigenous. In rich lowland habitats the difference between one year class and another is not so marked, the population being kept in check by predators, chiefly perch and pike, and possibly by disease. The catastrophic perch disease which swept through the country a few years ago resulted in the virtual extermination of the species in many waters. The disease is still active in^ a few waters, but now we are seeing a revival of the species in fisheries that were thought to be barren because of the disease.
Ruffe – perch’s poor relation
In comparison with the very extensive research that has been conducted on the perch, little is known of the ruffe. Variations in growth rates in different habitats have been observed, but the causes are not properly understood. The maximum
recorded lengths in the first four years are 8, 15, 18 and 19cm, but more usual figures are around 6, 9, 11 and 12cm. Most ruffe are sexually mature at the end of their first year, and all are by the end of their second. Spawning takes place on the
lake or river bed on exposed hard surfaces such as gravel, sand or clay in a series lasting from April to June. It is doubtful that ruffe live for longer than six years, or attain more than 25cm, specimens of this length having been recorded only on
the Continent. The ruffe is very much the poor relation of the perch – timorous and retiring, fussy about its spawning places, only locally distributed, relatively colourless, and small – and few anglers know much about it, and still fewer care.