Technique

Material for photography was obtained principally in the neighbourhood of Tiritiri Island. Fish were caught in a commercial trawl by the Fishery Research Vessel Ikatere, and immediately the catch was landed it was sorted for “running” snapper. The “running” condition is readily recognised by gently stroking the abdomen of the fish between fingers and thumb in a tailward direction. The eggs or milt if ripe are thus expressed through the cloaca. For the earlier developmental stages several fish were kept alive in a tank of running water until port was reached. Otherwise eggs were expressed and fertilised at once. Eggs and milt were collected in separate two-pound jars which had been previously quarter filled with clean sea water. After making certain that no faecal matter or immature eggs were included in either jar, the contents of the two were mixed. Sea water was added nearly to the top of the jar, which was then covered with number 40 grit gauze.

Ashore the samples were allowed to stand for about 15 minutes (except when early cleavage stages were required) until all viable eggs were floating at the surface. It was then possible to draw off a suitable quantity of eggs with an eye-dropper pipette and place them in a jar of freshly filtered sea water. Thus dead eggs and extraneous material which had sunk to the bottom were eliminated, thereby removing likely sources of bacterial contamination as well as foreign bodies which might mar otherwise acceptable photographs. It was found that any attempt at aeration was unnecessary, and in fact undesirable, since the disturbance of the water was liable to produce premature mortality, particularly in the larval stages. Thus, provided the water remained clear, no further attention was given other than protection from dust or extremes of temperature, and the removal of dead eggs or larvae. Any cloudiness or unpleasant odour was immediately eliminated by pipetting off all healthy material and placing in clean water. In order to prevent the spread of any bacterial contamination it was found desirable to use a separate pipette for each jar and to boil all used glassware before fresh material was introduced. Water temperature was taken at hourly intervals, though it was not always convenient to make a complete 24-hour record.

Material required for examination was removed by pipette and placed on a glass slide in a drop of filtered sea water, and when necessary irrigated until all particles of dust were removed from the camera field. The specimen was oriented by a current of water from the pipette, or by fine glass needles. The majority of photographs were taken without a cover glass and with the camera vertical. In the case of the lateral views, however (Plate 25). the whole apparatus was tilted to a horizontal position and the specimen contained in a flat-walled rectangular glass cell constructed by cementing a 2 × 1 ¼ inch coverslip with 1 mm spacers to a 3 × 1 ½ inch slide, leaving a space at one edge for introducing the egg or larva.

In addition to trawl catches, a series of plankton samples at all depths were made, in an effort to secure eggs and larvae in their natural state. Although eggs in all stages were relatively easy to obtain, the only larvae found in numbers were in a single vertical haul taken at night in about five fathoms at Bostaquet Bay on the south coast of Kawau Island. These were all in the same stage of development and had obviously hatched only an hour or two before being taken Owing to the scarcity of planktonic material and the apparent inability of larvae