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Zoology Publications from Victoria University of Wellington—Nos. 54 to 57

Materials and Methods

page 2

Materials and Methods

On 20.10.69 four egg masses on stones were collected from the western shore of Lyall Bay and kept in rectangular plastic containers (30 × 28 × 13 cm) at the Island Bay Marine Laboratory. The water was changed daily and kept constantly aerated using an eddy-current air pump. The stones with eggs were wedged at a 45° angle against the sides of the containers, with the egg masses on the ventral surface. Porous "air stones" were placed beneath the eggs so that the streams of small bubbles issuing from the "air stones" flowed over the egg masses. This method prevented the accumulation of detritus on the eggs and ensured an adequate supply of oxygenated water. Despite these precautions many eggs died and these were removed each day to prevent the build up of fungi and bacteria. The eggs adhered very closely to the stones and those required for observation were very difficult to remove without damage to the egg membrane. Limited success was obtained by sliding a sharp scalpel between the egg and the stone and then pipetting the dislodged egg into a petri dish. The identity of the above eggs as those of T. melobesia was confirmed by comparing these with thirty eggs laid on 30.10.69 by one of three females (22, 23, 26 mm s.l.), which together with two males (27, 29 mm s.l.) were kept alive in an aquarium. Development of these eggs and those obtained earlier was studied and sketches of the eggs and larvae were made using a binocular microscope equipped with a grid eye-piece. A micrometer ocular was used for measuring eggs and larvae. Measurements of the larvae were based on those recommended in Hubbs and Lagler (1958: 24–26).

Larvae larger than 5.3 mm were obtained during the spring by making regular plankton tows approximately 100 yards offshore at Island Bay from a small boat. The net used was of standard conical design with a two-foot diameter opening and a mesh size of 500 microns.