You never catch the black ones

Forest and Bird, Volume 14, Issue 3, 1 August 1982, Page 34

You never catch the black ones

By

Fisheries Research Division, Ministry of Agriculture and Fisheries, Christchurch

R. M. McDowall,

SMALL CHILDREN get immense pleasure from catching fish, usually from wharves and jetties, with hook and line, or in shallow backwaters and bays, with a small net. The picture of youngsters wading around shallow lake margins with a small round net and preserving jar is especially familiar. However, fish available for such activities in New Zealand’s rivers and lakes are rather sparse. Most of our species seem to live in bush-covered streams, in overgrown swamps, or in the broken-water rapids of the larger rivers; in all these places they are seldom seen and certainly are hard for children to catch.

IT’S THE FISH they can see, resting on the bottom or darting around in the open, that capture the attention and which are the target of budding anglers in the 5 to 10 years age group. Sometimes their ‘‘prey’’ is juvenile trout, but more often it is small bullies (Gobiomorphus spp.) they are after. Most usual among these are the common bully (GobiomorDhus cotidianus) and occasionally the upland bully (G. breviceps), with other species like the red-finned bully (G. huttoni), giant bully (G. gobioides), or Cran’s bully (G. basalis) sometimes being included. Abundant The common bully, as its name implies, is widespread and abundant, particularly in the lower reaches of the river systems and in lakes at all elevations. Its apparent abundance is accentuated by the fact that it is much less secretive than other species. It is quite normal to see common bullies darting around among the rocks in the marginal shallows, near lake margins, or beneath jetties. Other species are much more rarely seen. Observant youngsters notice that, especially in spring and summer, some of the bullies are jet black and others are a grey-brown, and it is their ex-

perience that though they can apparently catch the greybrown ones, they can’t catch the black ones. This apparently factual observation reflects an interesting peculiarity of the habits of our bullies. Highly territorial The male bullies are highly territorial in behaviour, especially in spring and summer, when they are spawning. The female must have a surface on to which she can place her eggs, where they will adhere, and where they will be safe from attack by predators. The male selects a_ site suitable for breeding. A flattish, firm, clean surface is required and usually it is beneath a rock, sometimes on the lower surface of a log or can, occasionally an old car tyre, and sometimes on the surface of plants growing in the water. Occasionally, too, it is On the upper, exposed surface of some such object. In preparation for spawning he clears it of silt, debris, and bottom fauna insects. The male lives in this territory,

patrolling it on a regular basis and chasing away intruders, especially other bullies. In addition to defending his territory and doing some ‘‘housework and maintenance’"’ the male has to lure a ripe female from the neighbourhood and so is engaged in courtship behaviour with females passing near or through the territory. Colour change Little is known about this courtship, but one of its consistent characteristics is that the male changes colour. Regardless of species, as far as is known, the male’s blotching and banding pattern is obscured by his becoming jet black. About the only relief from this black is the outer fringe of the first dorsal fin, which is Orange in some species (common bully and upland bully), green (red-finned bully), or blue (blue-gilled bully). This seems to be a nuptial colouration present during courting, spawning, and afterwards during the guarding of the nest site by the male. The male lures the female into the nest area, where she deposits the tiny eggs in a uniform layer over the chosen surface. After she has completed spawning, the female is probably driven from the nest, but evidence suggests that the male may then court another

female in the vicinity and repeat the performance so that there may be several batches of eggs on a rock, hatching at different times. The eggs are oval shaped and about a millimetre long; they form a compact, singlelayered mass, each egg attached to the surface by a group of adhesive threads at one of the pointed ends. Black colouration lost Unless otherwise interfered with, the male maintains his black nuptial colouration at least until the eggs have hatched several weeks after spawning. He stays in his territory, spending some time near the eggs beneath the nest rock, but emerging to patrol the area, to chase away intruders, and to feed on bottom fauna insects. It is on these patrols that he is seen by youngsters, and their Observation that ‘‘You never catch the black ones’’ has a rather simple explanation. It’s not that they can’t be caught; rather that once they ‘are caught and are seriously stressed by the experience, their bold, black colouration, designed largely to increase visibility during courtship and territorial defence, is rapidly lost and the fish return to their more usual blotching of sombre browns and greys — a colour pattern designed to assist concealment. The breeding habits of New Zealand’s six bully species are essentially similar to that discussed above, though some species have marine-living larvae (red-finned, common, blue-gilled, and giant bullies) and some do not (upland and Cran’s). In the marine-living species the eggs are very small, and the tiny larvae, on hatching, are washed down stream to the sea, where they feed and grow in the plankton, returning to

fresh water some 3 to 4 months later and migrating up stream at a size of 15 to 20 mm. Some common bully populations have abandoned the marine stage and have adopted a lake-limited life history, with the larvae living in the open lake waters rather than in the sea. The two species which do not go to the sea have much larger eggs, 2 to 3 mm long, and when the somewhat larger larvae hatch, they can be found in small, loose shoals in still water along river margins. Different appearance Another interesting feature of all species is that the sexes differ in appearance. Until this was understood it caused much confusion, some _ observers thinking that the male and female were of different species and thus recognising too many ‘‘species’’; other observers made the mistake of thinking that the fish were very variable in appearance and so recognising fewer species than actually occur in New Zealand. In all six species the male grows larger than the female and has a much blunter snout and distinctly larger fins. The male is also more handsome in appearance, in particular having much brighter colouration: the bright yellows, oranges, and reds described for various species are present only in the males. These differences are greatest in the red-finned bully. The male of this species has bright orange to crimson stripes on the cheeks, blotches and bands along the sides, and speckling in the fins. It is a particularly handsome fish, undoubtedly the most spectacularly coloured of our native species. By contrast the female has no bright colouration, but is much more sombre, with patterns of greys and browns.

Differences of this sort, though less extreme, are characteristic of all the species, males with some bright colouration, the females more plain and sombre.