Art. IX.—Further Experiments on the Influence of Artesian Water on the Hatching of Trout.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 43, 1910, Page 55

Art. IX.—Further Experiments on the Influence of Artesian Water on the Hatching of Trout. By C. Coleridge Farr, D.Sc., and D. B. Macleod, M.A. [Read before the Philosophical Institute of Canterbury, 19th October, 1910.] The experiments here described were carried out in conjunction with the authorities of the Canterbury Acclimatization Society at their hatchery in Christchurch, and our thanks are due to the Acclimatization Society for the facilities they have offered us, and to Mr. Charles Rides especially for the interest he has taken in arranging the eggs, &c., for us. The work conducted last year (Trans. N.Z. Inst., vol. 42, 1909) showed conclusively that the artesian water of Christchurch was fatal to a large number of fish confined in close proximity to the outflow of the well, and of those fish which survived only a very small proportion escaped pop-eye. Both these effects disappear on aeration of the water, which was shown to contain an excess of nitrogen, a defect of oxygen, some carbon-dioxide, and radium-emanation in solution. It seemed likely from the experiments carried on last year that the mortality amongst the eggs and also the development of “blue swelling” were troubles which were minimized by aeration, and to clear up these points, and, if possible, to throw some light on the particular factor producing these effects, the experiments here described were made. The Acclimatization Society very kindly placed at our disposal for the experiments two sets of hatching-boxes, one containing five trays, with a fall from tray to tray, and the other eight trays, with a similar fall. In each of these thirteen boxes 2,000 “wild” brown-trout ova were placed under the conditions known from experience in the hatchery to give the best

hatching results. reference to the paper already referred to will show that these conditions were entirely different from those adopted last year, when 7,500 eggs were placed in each of the five boxes of one of these sets, and the eggs were simply laid on the bottom of the box. On this occasion the 2,000 eggs were placed on a gauze tray at least an inch from the bottom, and the water circulated through the tray, flowing from the bottom upwards. It is no doubt entirely due to these better conditions that the death-rates to be given are so low compared with last year's, when the conditions were previously known to be such as would produce great mortality, both in the egg and yolk-sac stage. An examination of the radio-activity of the water of the top boxes in each set revealed the fact that whereas the activity of one set was 126, the same as last year, and expressed in the same units, the activity of the top box of the other set was only 78. As this difference existed between the radio-activity of the two boxes, a very careful examination of the gas-content of the two boxes was made. The results appended are a mean of five determinations of each box, and in no single case did the result differ appreciably from the mean. Box No. Emanation. Gas-content. 2,000 Brown Trout. 2,500 Rainbow. Eggs. Blue Swelling. Blue Swelling. Boxes on Right of Door. 1 126 N 16·35 252 70 102 O 4·30 (254) (72) CO2 2·60 2 111 302 68 88 (224) (72) (87) 3 95 167 41 73 4 83 214 33 71 5 69 N 15·35 184 29 58 O 5·45 (28) (57) CO2 2·53 Boxes in Front of Door. 1 78 N 16·31 156 34 97 O 4·76 CO2 2·37 2 75 N 16·00 163 38 142 O 5·15 CO2 2·45 3 73 184 35 80 4 185 36 87 5 198 33 70 6 154 38 57 7 36 N 15·20 195 31 52 O 6·35 CO2 2·43 8 172 30 37

A glance at these figures will show that, while the two top boxes are practically identical in nitrogen-content, that supplying the set of five trays has a little less oxygen (0·46 c.c. per litre), but has an emanation content 1·6 times that of the other. Under the headings “Eggs” and “Blue Swelling” are given the numbers of deaths as eggs, or in the yolk-sac stage due to blue swelling, as the case may be. The figures in brackets indicate the same quantities in check boxes occupying parallel positions to those in the same square. Only a few such parallel boxes were used in the one set of trays. The last columns in each set are not strictly comparable. They refer to the same class of fry which were hatched from “pond” and not “wild” ova, and in the longer set of trays we had only a few eggs at the end of the hatching season to experiment with, and the results were raised to the 2,500 basis for comparison. The discussion of these figures in conjunction with last year's results show, we think, that both the death of eggs and also blue swelling decrease as the water becomes more aerated, and this seems to be more the case in the set of five boxes than in the set of eight. It may not be considered to be very marked as regards eggs in either set of the brown-trout ova, but it was very evident in the same set of boxes last year, when 7,500 eggs were hatched in each box. Taking the figures as they are, while it cannot be said there is any falling-off in the number of deaths in the eggs in the set of eight boxes, there is a slight falling-off in the set of five boxes, and a distinctly greater mortality on the whole, especially in the boxes nearest the well. As regards blue swelling, whereas in both sets of rainbow fry, and in the set of five trays with the 2,000 brown trout, there is a marked falling-off from box to box, yet in the set of eight boxes it seems that the mortality, as with the eggs, is practically constant. It would appear that, taken as a whole, the figures obtained last year and these indicate that both these troubles are due to want of aeration, though it cannot, of course, be denied that some eggs would die even though river-water perfectly aerated were used. The hatching season is short, and the whole of the hatchery cannot, of course, be handed over to experiments of this kind, and hence the results are meagre, and conclusions as to the particular constituent in defect or excess which is the cause of the mortality must be drawn with caution. If it be admitted that the mortality depends to some extent on the aeration, then we think it can only be due to defect of oxygen or excess of radium-emanation. Besides the improbability of so inert a gas as nitrogen affecting the fish, the very small percentage differences between the nitrogen-contents of the two top boxes would further reduce the probable effect of nitrogen. At present it is practically impossible to decide between a defect of oxygen and an excess of radium-emanation. Both these tend to disappear as the water is aerated, so that the two cannot be well separated. We hope we may be able to perform crucial experiments by confining goldfish in a limited supply of water containing sufficient radium-salts to produce the emanation in quantities comparable with that in the wells. By such means one of the two factors could be eliminated.