LIFE OF WHITEBAIT.

Waikato Times, Volume 108, Issue 18167, 4 November 1930, Page 2

LIFE OF WHITEBAIT.

SPAWN IN GRASS. EGGS LEFT HIGH AND DRY. The investigations being carried on > at present by the Marine Department into the life history of the whitebait (Galaxias attenuatus) are proving most fruitful, and when the complete text of the results obtained by Captain L. Hayes, which will form the subject of a treatise to be published in the Transactions of the New Zealand Institute are published the public will realise that so much that is new has been discovered in regard to whitebait that many conceptions of its habits have been proved erroneous (remarks the Wellington Post). Not only that, but the commercial aspect of the whitebait, important in view of the few legitimately possible New Zealand industries free from strangling protective tariffs, will assume greater importance. When it is realised that the adult whitebait (the common minnow, or inanga) spawn at the limit of high-water mark amongst the grass in about an inch and a half of.water, the eggs remaining fertile provided there is sufficient evaporation from the soil to keep them moist, for periods ranging to as many as fifty days, and that this • spawning is done within a few miles of the mouths of New Zealand rivers, the damage caused by the grazing of these lands by heavy-footed stock may be readily assessed. In a piece of turf some seven inches in diameter the size of a draught horse’s footprint—6o6o whitebait were recovered by artificial hatching, the unfertile eggs pjroving a very small fraction of the whole. The report of the Marine Department to the Government says, under “scientific investigations"; “Until the gaps in our knowledge of the life his- ( tory of this species could be filled up' we were not in a position to tackle the framing of regulations for its conservation with due insight into the fundamental facts of the situation. In particular, it was recognised that light should be thrown on the spawning of the species. Besides the wellknown fact that whitebait, which are inanga at a juvenile stage, enter the mouths of rivers from the sea, there existed convincing evidence that the adults when about to spawn migrated in shoals from fresh water down to tidal water. The Maoris believed that the inanga spawned in the sea, and this view has been accepted by European and New Zealand writers on the subject. • Spawning Mystery Solved. “The exact location and identification of the naturally deposited spawn and the distribution of the larval (pre-whitebait) stages were unknown until the department’s investigations were made. Some preliminary light was thrown on the subject when, in May, 1929, ripe inanga oi both sexes were obtained from the YVhakapuni draifi near Foxton, and the ova artificially fertilised by Captain L. Hayes. Different lots of these ova were ,kept (luring the incubation stage in water of four different grades of salinity—(l) Seawater from Wellington harbour, (2) a mixture of two parts seawater and one part fresh water, (3) a mixture of one part seawater and two parts fresh water, (4) fresh Wellington . tap water (derived from the Wainuiomata). “The somewhat surprising outcome of this was that healthy larval fishes hatched out from each lot, indicating that both eggs-(embryos) and larvae were toleraht to either fresh, brackish or salt water, which is in itself a very exceptional phenomenon. It suggested that the natural incubation of this species took place under very variable conditions with regard to the salinity of the surrounding 'water, such as would be found, for instance, near the mouth of a tidal river. It was also found that the eggs preserved their vitality when kept packed in-damp moss for several days. By this experiment also the character of the egg and of the newly-hatched larva was determined —a necessary starting point for the identification of the same when found naturally occurring. The number of eggs produced by a single female inanga has been found to vary from 1500 in the smallest (2|in) fish to over- 13,000 in a very large (5 in) specimen.

A High-tide Romance.

“A further step now to be recorded 1b the actual observation of the act of spawning, the location of the spawn, the incubation period, the emergence of the newly-hatched young fish, and. their natural distribution. These observations were carried out by Captain Hayes on the Manawatu River between” about three and a half and eight miles from its mduth, on a visit made about the . middle of March, 1930, and on subsequent visits. The main 'facts which he brought to light are as follows—The ripe fish migrate to the tidal water in shoals, arriving at the time of spring tides. These migrations were observed to take place in the Manawatu River this year in March (once), April (twice) and May (twice). There was evidence to support the supposition that a spawning had also taken place in February. For spawning the shoal approached the very margin of the river at the time of high water. The minute eggs are deposited among rushes, grass, or other vegetation which affords concealment for the spawning fishes and cover for the eggs, which adhere in masses on the ground about the bases of the stems of rushes or grasses. Spawning did not take place till the highest of the spring tides had pass Gd. * * “The ova were thus left ‘high and dry’ when the tide receded, and, since they were deposited as near the water’s edge as the fish could get, and the tides which followed were of diminishing height, there could be no further contact'with the water until the next spring tides occurred. The spawn is thus assured complete protection from any aquatic enemy for practically the whole of the incubation period. When the eggs are once more submerged on the next spring tide reaching them hatching takes place, and the larvae are carried down by the ebb tide. At the time when the eggs were hatching out considerable quantities of the larvae were taken by tow-netting in ‘thq estuary just above the bar. It has been demonstrated that if the spring tides succeeding the one on which spawn-, ing took place are not so high, and therefore do not reach the zone where the spawn is . deposited, the embryos remain unharmed, while hatching' is deferred. An Unguarded Danger. ••The period between spawning and hatching may thus be about fourteen days, or it may be extended _to as much as forty-eight days. This provision by which the parent fish de-

posit their spawn at places which are only covered with water .at the highest lidds practically ensured immunity from enemies under the original natural conditions which held previous to the colonisation of New Zealand. Under present-day conditions, however, adverse factors come into play which were not contemplated, so to speak, in the original natural state of affairs. In the locality investigated it was found that horses, cattle, and- even human beings, by trampling over the ground on which the whitebait eggs were deposited in hundreds of thousands, wrought a considerable amount of destruction.