With respect now to some facts: it had been said that the water was salt, because this pond was situated at a sea [p322] embankment. I stated before, that it admitted the sea, by leakage, in summer, when there was little comparative supply of fresh water, and was therefore brackish, or saline. I have since ascertained the exact proportion of salt in the water, at those times when the fresh water is least. In the driest and hottest part of one summer, the proportion of salt in it, as compared to the sea without, was as 40 to 150. In another, peculiarly dry, 1827, it was one half; and the water, having then been at the lowest, it cannot ever be computed to exceed this. Moreover, this period of saltness cannot easily, even in such a summer, occupy more than the months of June, July, August, and September; or, more strictly speaking, it is probable, scarcely one half of that time in general, in so rainy a climate; a climate equalling Penzance in the quantity of rain.
In winter, that is, during five or six months, or less, if any objector pleases, it is fresh. That cattle drink it freely, is not an exact chemical proof; but I must admit, that I have not analyzed the water at that period, holding the objection in great contempt. It may be sufficient to say, that it then occupies a space of about sixteen acres, or increases to this magnitude from four and a half acres; so that it cannot, at least, be very salt, while the fish, and the mullet in particular, are found in the remotest ditches, among the meadows. But, in defect of an analysis, which I have not had the means of making, there is a valid reason why the water should be fresh when the size of the pond is much extended. The presence of sea-water in it, is, in all cases, the consequence of a depression of the water within the sea-wall, which allows of leakage or infiltration at the upper part, so as, in high tides, to equalize, as far can be done in the short period of high water, the levels within and without. This, it is plain, must cease whenever the water within is higher than the sea without; and hence it is that there can be no access for the salt water in the winter or rainy months.
Enough of the mere fact: the objections derived from which ought not to demand an answer among physiologists; while to those who argue physiological points in utter ignorance of all that belongs to physiology, it is probable that all answer is fruitless. It was stated before—the question is simply twofold; [p323] respiration and food. If fish can breathe indifferently salt water or fresh, for one week or one month, and if, in their new element, translated from salt to fresh, they thrive or grow, fatten and breed, the trial of three weeks or three months is a sufficient proof that they will neither sicken nor die of fresh water. If they can find food, it is indifferent whether the medium is fresh or salt. It is the misfortune of the age to understand every thing without knowing its principles; just as every man is now a physician. A few, more profound, who chance to know that salmon divide their time between fresh and salt water, possess other reasons, and find other objections; which they must be permitted to explain for themselves. I ought not, while on this particular subject, to omit one fact, which has come to my knowledge since the former papers were written, on the voluntary emigration of a fish, supposed to be peculiarly delicate and peculiarly attached to the sea, into fresh water. This is, that, in Virginia, the herring ascends the rivers, even up into the most minute communicating branches, and as far as it can reach; while a somewhat recent traveller describes them as being so abundant, that it is impossible to cross the fords on horseback during the season of their migration, without destroying them by the horse’s feet. To proceed to the historical condition of this pond.
I have already stated the difficulties arising from want of leisure and wealth in the proprietor, added to non-residence I should say, whence chiefly has arisen the difficulty of tracing the results. Let those try for themselves, who consider that all this might have been ascertained in a twelvemonth, and with the same means. Since the communications I formerly made, the Pilchard has been introduced. It swam away briskly, therefore it would not die of the fresh water; but it has not been retaken. The retaking of individual fish, to ascertain their presence, is a fundamental difficulty, as I before pointed out.
The Brill has also been introduced since my former list. It has been retaken; and, within one year, had grown to double the original size.
The Turbot. Fifty or sixty were introduced, averaging about eight inches in length. Some were retaken in a year, for the purpose of examination merely, like the former and most others; [p324] they also had grown to double the size. There is no prospect of dying in these cases, it is abundantly plain; that they will breed is probable, but there has been no time, nor would the young have been taken. What is to prevent healthy fishes from breeding? The young, indeed, may be eaten; if so, it is for want of room, or want of a proper balance in this mixed population. No one knows any thing, either of the ordinary growth, propagation, or destruction of fishes; and how then can any one decide on what is regular or extraordinary?
The Wrasse has been retaken after a considerable period; therefore it is not dead.
The Basse has propagated; and so has the Brill.
The Red Mullet has been introduced, and is living.
The Whiting was introduced, and taken in good health many weeks after, but not since.