Fundulus diaphanus diaphanus

      By V. B. Hunt
      reprinted from Lateral Line, March 1981

The American books I have in my possession refer to this species as the Banded Killifish for want of a better name, though a fair percentage of the Fundulus species are striped (banded) anyway. It occurs throughout the greater part of the Atlantic seaboard of North America from Newfoundland to South Carolina and inland as far as the Great Lakes Basin. The nature of its environment varies from the brackish waters of the river estuaries to the fresh waters of inland lakes and ponds.

I found this species particularly abundant in the northern counties of New Jersey where there are numerous lakes with open, sandy shallows and thick underwater plant growth in the lower depth: highly suitable for its breeding requirements. It is in some degree a schooling fish though only in small numbers it seems, and in the sandy shallows I found this torpedo-shaped, fast moving killie quite difficult to catch, even with a two feet diameter hand net. I had to be contented with youngsters, the 2-3" adults proving to be too much of a handful.

I naturally wanted to bring back to England a number of small specimens, and this I was able to do with little difficulty. The banded killifish has proved itself a good traveler in more ways than one, in fact, or rather as I have been led to believe, the anglers have been known to transport this popular 'live bait' in boxes packed with damp moss with little detriment to the fish! Mine, needless to say, were transported in water!

Initially I housed about ten of this species, four of which were males, in a 30" x 15" x 15" tank planted out with Sagittaria subulata natans, Elodea canadensis and Myriophyllum verticillatum and a fine gravel bottom. The back of the tank was near a window facing south and in order to restrict the obviously high temperatures I would encounter during the summer I covered it with a thin sheet of polystyrene. During the hot summer of 1976 the water temperature went as high as 85 degrees Fahrenheit but knowing the species fairly well I wasn't particularly concerned - Fundulus diaphanus has a very high temperature range, 32 to 90 degrees Fahrenheit. The males which are, incidentally, slightly smaller than the females, develop a beautiful pale-blue colouration with marked iridescence in the 16-20 stripes and the finnage at the height of summer. The females are olivaceous with about twelve, somewhat shorter and wider apart black, vertical stripes.

During a particularly hot spell of weather there was much activity in the tank; the males were vigorously chasing the females in typical killie fashion, frequently squabbling for the attentions of the fattest, and me, full of hope and anticipation, wondering if this species had ever been bred in this country before. Unfortunately my supervision was somewhat lacking and I delayed the separation, the result being the loss of a great number of eggs. This was a tragedy, but I suppose I had to excuse myself a little under the circumstances; this species had revealed itself as an avid egg and fry devourer, and I had little chance of salvaging what was left. All in all only four youngsters escaped the ravages of their parents.

Technically speaking the breeding of this particular fish in the aquarium takes on a somewhat regimented appearance; the males and females pairing off, not always agreeable, according to size. Each male pursues its individual female during which time the genital papilla of the female become enlarged. It is during the pursuit that the female reveals just the one single egg suspended about 1" on a fine translucent thread from the papilla, resulting in additional excitement from the male, who eventually wraps himself around the female in the usual fashion. The female produces more eggs, this time in a cluster of about ten. The male bows his body quivering rapidly, milt is produced and the eggs are fertilized. Each egg has its own individual thread and during the further course of sexual activity they become entangled in the water plants. The entire mating session described takes less than a minute. The same procedure is repeated until about fifty eggs have been produced. Regarding the rate of growth, a young diaphanus can be anything from 1/4" to 2" long in its first summer. The size of each egg, incidentally, is quite large, being 2 mm in diameter and the hatching period is anything from 10 to 14 days, depending on temperature.

My initial trial run of breeding this species in the aquarium, leaving it, as it were, to its own devices, had to be a failure but I did learn something from it. It was perfectly obvious I had to use more care, though this couldn't always be possible because I work for a living. I chose the easy way out, particularly as I was due for another trip to the States. I had already established three 5' x 2' x l' breeding troughs outside in the garden, two of which had a good bedding of silver sand at one end and heavy planting of Lagarosyphon major at the other. Over a period of time there is the inevitable development of blanket weed; not always desirable but it has its uses and this I found to my advantage, for in one of the troughs the entire perimeter of open water area was taken up with the stuff.

Fairly early in the year, around April time, I introduced half a dozen banded killifish to the outside I pond in question and again left them to their own devices and sure enough, towards the end of June, just before I left home for the USA they spawned; in fact judging by the two distinct sizes of the fry I observed on my return there must have been a second spawning within a fortnight. Despite the fact that a number of the youngsters must have been eaten, an appreciably high percentage had evidently escaped into the blanket weed. They were of good size and lively enough to keep away from their ever voracious parents. The blanket weed, as I said earlier, has its uses; apart from being an avenue of escape it acts as a good spawning medium and an excellent producer and harbourer of infusoria. Thus the young fishes developed, and after a period of six weeks the first spawning was nearing 1/2" in length. My breeding troughs are situated in a sunny position against a wall facing south, so despite the poor summer we had that year there were days when the water temperature reached the low 80's.

I mentioned earlier the size of the fish. According to all the books I have read on the subject it is a fish that can reach 4" in length though only rarely will it do so. An average large adult female is about 3-1/4" with the male 2-1/2 to 2- 3/4". I am going on fishes I have observed in the rivers and lakes of New Jersey and of course those I have reared at home.

On the subject of feeding, I have found that Fundulus diaphanus ignores flake food but will take split blowfly maggots and earthworms (if the fishes themselves are big enough to take them), tubifex and water fleas, plus of course bloodworms, mosquito larvae and the like. Also this species is not impartial to a small percentage of plant food. There is one set-back, however, with this fish and that is its nervousness. On occasion I have seen my charges in a line across the front of the aquarium awaiting their food, but most times they will remain hidden away and seemingly it takes a considerable amount of courage on a fish's part to venture out of its safe corner to collect a freshly dropped tidbit. In its panic it invariably misses, makes another attempt to catch the desirable morsel only to miss again and finally disappears into the foliage of its pet cubbyhole 'empty-handed'. An erratic species I must accept, as on occasion it has nibbled my fingers on the surface of the water! Yes, my patience is tried but the food my charges have refused is always picked up from the bottom after I have left the fish house!

I originally wrote this article three or four years ago, I cannot remember exactly, and I wondered at the time whether or not anyone else in the United Kingdom had bred this species and to this day, as a result of conversations I have had with B.K.A. members the only part of England where Fundulus diaphanus is to be found is my very own back garden. This species cannot be purchased in any shop, and I had certainly never seen a 'banded killifish' until I caught my own specimens in the wild. The possibility is then that I could be the first person to have bred Fundulus diaphanus in this country, though such an 'honour' is watered down somewhat when one considers it has proved itself a ready and easy breeder in the aquarium. I have considered utilizing the well-tried woolen mop method for 'safe breeding' though I don't consider it really worthwhile; I can guarantee a spawning every year in my outdoor breeding troughs. As a footnote I would like to point out that my title, Fundulus diaphanus diaphanus referred to the Eastern Banded. There is a Western Banded Killifish, Fundulus diaphanus menona.

Used with permission. Article copyright retained by author.

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