Fish hatching, as practised in Otago with Trout Ova.
This interesting process, in pursuance of the arrangement proposed in the beginning of this paper, I will now endeavour to describe. As at home so here, the winter season is that during which we find our acclimatized trout effect their spawning. Or rather I should say that while trout in England and Scotland spawn in October and November, we find that in Otago they do so later, that is from the latter end of June to the end of July, and sometimes on to the middle of August, which months correspond to December, January, and February in Britain. Previous to the winters of 1879 and 1880, besides ova taken from spawning fish in the Water of Leith, ova had been got from the natural spawning beds or “ridds” in Lovell's Creek, Fulton's Creek, Lee Stream, and Shag River. This was done by the Acclimatization Society, by whom the trout were introduced, and who have power by law so to do; Mr. Clifford, the original and successful acclimatizer of these fish, being now succeeded by Mr. Deans, the society's manager, a most careful and trustworthy operator. But during the winters of 1879 and 1880 the ova have been entirely got from fish caught in the Leith.
The spawning fish. A mild night, without moon but not too dark, and the water clear, are the most favourable conditions under which the fish may be taken. Provided with a lantern throwing a good strong light, attached to a waist belt or carried in the left hand, a large scoop net in the right hand, and his legs enveloped in gum boots or waders, the manager quietly enters the bottom of a pool. His attendant, carrying a large metal bath or tub for transport of the fish, moves along the bank of the Leith, and keeps near him. On approach, a fish, which can readily be seen by an experienced person, moves up stream, slowly, however, as compared with what its movements in daylight would be. By quickness the net can generally be passed under the fish ere it can get away, and should the fish
be near spawning or milting, it is at once transferred to the tub with a sufficient supply of water. Thus confined the trout shows considerable restlessness at first, but gets soon more reconciled seemingly to its novel habitation, as it becomes more quiescent. But should the fish when taken not be near maturity or ready to propagate, it is returned to the river for a time. Working thus up stream, pool by pool, and stream by stream, so much only of the river is gone over as gives a number of fish sufficient to transport in the tub. When this is attained, Mr. Deans and his man carry the tub and its contents carefully to an enclosed stream or small pond, within the gardens. This is called the “hospital” or the “lying-in pond,” and there the milters and spawners are kept till ripe or ready for stripping. More than a score of trout, some 10 lbs. to 12 lbs. weight, have thus been caught on a good night, but some nights scarcely a fish can be seen or taken in the Water of Leith. A deep hole with a weir and apron below Anderson's flour mill, is a favourite resort where numbers of large fish congregate.
As regards the greater ease of taking fish by a lantern or torch at night, than without that and during daylight, it has long been held as an opinion that the fish become so dazzled or dazed by the light as to be incapable of swimming away. From my own observations, however, when assisting in the capture of trout in the Leith, I can only admit that the above opinion is partially correct. The light appears (particularly when a dark-lantern is used) to rivet the attention or eyesight of the fish, to the exclusion of the darker body of the man, so that but for the motion of the light the fish would probably not recognize its danger. But as the light moves, so does the fish, and should the rays fall on part of the man's body or on the net, its motion is quickened, and it makes off.
The proportion of males are few compared with the number of female fish captured, so far as I have seen. Thus I was present on the 10th of July last at a stripping of trout at the lying-in pond, when only three or four males were got, while there were twenty-four females handled ! So also in angling I always catch far more females than males, as on March 26th, 1880, out of thirteen trout I caught in the Deep Stream on that day and the following one, there were not more than two undoubted males. In connection with this I may refer to the fact that some years ago I and others caught male trout in the Lee Stream, which were lean and emaciated and evidently wasting away from some unexplained cause. That cause was certainly not want of power or inclination to feed, as they took the fly or bait greedily.
The colours of the trout during the spawning season here, are deepened, just as has beeen remarked with the Salmonidæ at home. For example, on the occasion of stripping just mentioned above, I noticed that the males, and more particularly the larger ones, were very dark and golden tinted, the fins, and notably the adipose and caudal, having much deep pink; while the
spots ‘ black and crimson ’ were very conspicuous. The females were clear and silvery, like sea trout, and crimson spots were visible, which probably in the summer season would not be discernible on the same individuals. The hook on the lower jaw of the males seems to grow larger and softer during the spawning season in our rivers, just as observed elsewhere.
As the Water of Leith is a small stream, and the trout taken for stripping are often of great size, 10lbs. to 16lbs. in weight, the manager when done with the fish, and on their recovery, has for the last few years returned only the lesser fish to the Leith, the larger ones being removed to the Waikouaiti, Waitati, Silverstream, Waitahuna, Clutha, and Waipahi rivers; or put them into the Waihola and Tuakitoto Lakes, and the Tomahawk lagoon. The object of this is to make room in the Leith for the growth of the younger trout.
Stripping the fish.—A crockery basin or bowl being ready, having a small quantity of pure water in it, the female fish ripe for stripping is removed from the tub wherein she and others have been placed temporarily. The fingers of the left-hand, if a heavy fish, are passed through the gills and the tail is seized by the right. Lifted thus from the tub, so soon as she becomes manageable, the left hand and knees keep her in position over the basin, while the fingers of the right passed gently down her belly from above the ventrals to near the vent, effect the stripping. If the female be very ripe the eggs will flow with little or no pressure from the fingers, but if not, then a certain number only may come away, when she is returned to the lying-in pond at once, and allowed to mature. * When stripped the poor female trout has a very collapsed appearance; the belly, which before was full and distended, being empty, straight, and doubled in! On being, however, returned to the pond she soon recovers, very few ever dying from the effects of this artificial spawning. A short time—not more than a minute and a half or two minutes—suffices for handling thus a fish. Next in order, when the basin is full enough (it should not have too many) of eggs, a male is got, and similar handling with that just described gives the necessary quantity of milt, provided the fish be ripe. The milt from one male we find quite sufficient to impregnate the ova of several females, and that of a young male seems to be as efficient as that of a more mature trout. The milt and eggs are stirred gently with a spoon to ensure thorough contact. The female eggs are of a glossy dark pink colour on passing from the ovaries, but I have noticed a faint yet distinct alteration to a semiopaque and slightly milky tint, on impregnation taking place. I have preserved specimens of unimpregnated and impregnated eggs in glycerine, so as to retain the natural colours, and this difference in certain lights I believe I can still distinguish.
[Footnote] * Mr. Howard, of Wallacetown ponds, uses a board with netting attached to one side to secure the fish during stripping.
Occasionally, but not often, we have found a female give eggs of a light straw colour, and these have hatched out quite as well as those of the ordinary hue, with no difference in time, or in the appearance of the fry. On August 28th, 1880, we had in the hatching boxes at Opoho, ova of this colour from two females of 5lbs each, it was also much smaller than the pink ova from equally heavy female trout. This peculiarity in colour has been observed to occur sometimes with trout in English rivers, as mentioned by Mr. Frank Buckland, in his book on “Fish Culture.” In this last season's stripping one female gave 30 eggs much larger, twice the diameter of her other eggs, and as big as Californian salmon ova. They were of a light violet colour, and most hatched out, but 17 only survived, and these are thriving well and are kept by themselves. Her other ova were of the usual size and colour.
As to the number of ova produced by our trout, we find it to be 800 to 1000 for every pound weight of the fish.
Hatching boxes.—The hatching boxes and house, dam, and ponds for the young fish, are on the banks of the Opoho Creek, at the north end of Dun-edin. The place is awkward of access, but excellently chosen as regards coldness of water and protection from the sun's rays. The creek, flowing as it does down the shady side of Signal Hill and through bush, is cold, but has a considerable quantity of vegetable matter in solution (see analysis given above); not too much, however, as we have found, by the health and success attending our young fish, reared in it. The arrangement of these breeding ponds and the water supply is shown by a diagram which I have made to accompany this paper (pl. XIV). The water passes from the dam through a small fluming of timber four inches by four inches, past the hatching house to the fish ponds, and after flowing through these is allowed to discharge into the creek. At the hatching house a small pipe connects this fluming and the filter-box. The filter-box consists of two chambers, into the first of which, containing the filtering materials, the water flows from the box fluming. The water then passes through the bottom of the partition into the second chamber, where it rises and is drawn off by the several pipes as wanted, which supplies the hatching boxes. These boxes, twelve inches by six inches, built of planks one inch thick, and from four to seven feet long, are placed in parallel rows on either side of the hatching house. Each has sufficient inclination given to it to secure a gentle flow of water, the water passing through a zinc grating from one box to another. Clean gravel about an inch deep, being the debris of trap rock from the Opoho Creek, covers the bottom of each box, and the water, to the depth of two inches, covers this layer. The hatching house is boarded with Hobart Town palings, and has a calico or scrim roof resting on battens.
Hatching the ova.—In these boxes, as just described, the impregnated ova are carefully put and distributed all over the gravel in a single layer, wooden covers being then put upon the top of each box. Wide-mouthed bottles drop in the ova well. Notwithstanding all care, there is always more or less of a deposit from the water on the eggs, particularly at the lower ends of the boxes (see note in appendix). This, however, we have never found injurious, though it is objectionable. It can be removed by a camel hair brush, moving the water with a spoon, or increasing the flow of water, the latter being a cure to be avoided if possible. I may here mention in passing, that Mr. Frank Buckland made some experiments to ascertain what weight would be required to crush the eggs of the salmon, when he found it to be 5lbs. 6ozs. I have not tried what trout eggs will bear, they are considerably smaller than those of salmon of equal weight, but that fact does not indicate lesser strength, and it is very probable that they are as strong as those of the nobler fish. This astonishing strength seems to be a wise provision of nature, as in the natural ridds the ova of both these fish are liable to rough treatment and great pressure from superincumbent gravel.
The period of incubation, if I may use the expression, is found at the Opoho ponds to average 78 to 88 days under ordinary conditions of weather and the time from impregnation till the eyes of the fish appear, 45 to 50 days. A difference in the temperature of the water of 1½ degrees is found to make a difference of 10 days in the time of hatching. The average temperature ranges from 42° to 52°, but the strongest and healthiest trout hatch out in water at 48°. The period of hatching is from 8 to 14 days, that is between the first and the last trout breaking out of the egg. The umbilical bag in the young trout hatched in September and October, 1880, took from 50 to 56 days before it was entirely absorbed. From the time of the sac being absorbed the fry are fed with grated raw liver until liberated, the sac being supposed to contain all necessary nourishment up to the time of its disappearance. In Yarrell's “British Fishes,“p. 269, experiments in trout rearing in Germany are referred to, where the time from impregnation to the eye appearing was 21 days, to the hatching out of the fish five weeks or 35 days; and from hatching out to the absorption of the umbilical sac three or four weeks or 28 days. Thus it would appear that the trout reared at the Opoho ponds take as nearly as possible twice as long as fish in Germany to pass through the same stages from impregnation to absorp-tion of the bag. Some tables at the end of this paper may be found useful, giving a few details of temperature and hatching out in Otago. The 1879 fish grew much quicker than those of 1880, which were remarkably backward.
The young trout.—After hatching, the young trout (as stated above) are fed with grated raw liver, and this food is continued to them for some time after. They thrive very well on it, and feed, as we believe, on small water
insects besides. After hatching the young fry will be ready for turning out into the rivers in from 30 to 50 days, and will carry best whenever they begin to feed, which is from 25 to 28 days after birth. When they are about six weeks old, if well fed, they average 1½ inches in length, and at 100 days three inches. Parr marks or dark bands distinguish the young trout, just as in young salmon and sea trout, and in number I find these to be from 10 to 13; but the same individual does not always have an equal number on either side, just as they seldom or never have been found by me to have equal numbers of spots on the gill-covers on either side of the head. The parr marks disappear when the trout is four to five inches in length.
In transporting these young fish, Mr. Deans prefers to do so when they are from three-quarters to an inch long. He used to put water-cress into the water in the cans, but more recently he has not used anything but water, and has conveyed the young trout just as successfully the one way as the other. The great objects to be kept in mind in this operation are coldness and thorough aeration of the water, and also avoidance of crowding too many fish into one can. The cans used are conical in shape, the base being from 12 to 15 inches in diameter, and the top or mouth about 6 or 7 inches in diameter, and furnished with a lid which fits exactly. The height of each can is about 15 inches, and it has a perforated false bottom fixed in about one inch above true bottom. Aeration is generally found to be secured by the motion of the railway train or other vehicle conveying the fish. At other times a pannikin used occasionally will do as well. A can of the above dimensions will carry about 500 young trout of one inch in length, but that number should not be exceeded.
On arrival at the river or stream destined to be the future habitat of the young fry, they are liberated if possible in shallow water, with a coarse gravelly or stony bottom. On their escape from the can to the river, they rest for a time on the bottom, as if fatigued, thereafter going off according as their instinct directs them. On one occasion in January, 1880, I remember in company with Mr. Shennan, of Conical Hills, putting about 500 young trout thus into a shoal part of the Pomahaka River, and on our return in a day and a half, we could not see a single one, not even a dead one, of which there were some dozens at least. The river had been up a little in the interval and was slightly discoloured, so possibly they had shifted their quarters, or been compelled to do so by the action of the water.
It need only be added here, that as it is believed that the stock in any river will decrease (where fishing occurs) from year to year if left to itself, (indeed the experience of Europe and America has demonstrated the fact), the Otago society is very properly spending a large portion of its funds yearly in those operations which I have given now in detail as above. Thus only will the stock of trout in the rivers be maintained.