Introduction

Tripterygion capito Jenyns, 1841 and T. robustum Clarke, 1879, are endemic tripterygiids abundant in areas of seaweed and rock throughout Wellington Harbour and along the shoreline of Cook Strait, New Zealand. Both species occur around all New Zealand and are found throughout the intertidal zone. There are several other tripterygiid species in New Zealand but the systematics of these are at present confused.

Tripterygion capito is relatively small (maximum size 70mm s.l.) and individuals are generally dark in colour although many specimens appear silvery - grey with dark dorso - lateral bands from head to tail. Tripterygion robustum is larger (maximum size 105mm s.l.) and characteristically has a blunt rounded forehead. The colour ranges from a uniform black to light green with irregular greenish-brown patches. The anal fin is often fringed with white.

This paper describes the egg and prolarval development of the two species. Graham (1939, 1953) has briefly outlined the egg and prolarval stages and spawning behaviour of T. varium (Bloch and Schneider, 1801) from New Zealand.

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Materials and Methods

On 1.7.70 15 adult T. robustum were placed in an asbestos aquarium (2.5 × 0.38 × 0.23m) at the Island Bay Marine Laboratory. Several stones and Haliotis (paua) shells were placed in the aquarium to provide shelter and objects on which to spawn. The tank was supplied with fresh running seawater and the fish were fed chopped liver and fish. On 8.7.70 freshly laid eggs were found on the undersurface of one of the Haliotis shells. These were attended by a male T. robustum (78mm s.l.) which, along with the eggs, was removed from the asbestos tank and placed in a small plastic aquarium (30 × 28 × 13cm). The water was changed daily and kept constantly aerated.

On 25.7.70 a similar system was set up using 10 adult T. capito, but no spawning occurred. However on 28.8.70 an egg mass on a portion of clay pipe was collected from the Island Bay shore and kept in a plastic aquarium (30 × 28 × 13cm), along with the adult male T. capito found attending the eggs. The water was changed and aerated in the same manner as for T. robustum.

Eggs of both species required for observation were easily removed from the substrate by sliding a scalpel or mounted needle beneath the egg and then pipetting the dislodged egg into a petri dish.

Development of these eggs was studied and sketches of the eggs and larvae were made using a camera lucida. An ocular micrometer was used for measuring eggs and larvae. Measurements of the larvae were based on those recommended by Hubbs and Lagler (1958), with the exception of head length, taken here as the distance from the tip of the snout to the back of the otic capsule. This is more definite than the opercular flap which is often not readily visible. Egg and larval terminology is based on that used by Rugh (1948), Balinsky (1965) and New (1966).

Spawning and Development of T. Capito

In the Lyall Bay and Island Bay area near Wellington T. capito spawns from mid-July to late October. Egg masses are found from mid-tide to low tide levels in areas of rubble. The egg clusters are comparatively small measuring about 7 × 4cm and containing 2-3 hundred eggs. The eggs are laid close together forming flat, irregular shaped masses.

The egg clusters may contain groups of eggs at different stages of development, suggesting differing spawning times on the one substrate. In situ the eggs are colourless, pale pink or pale orange, the latter being associated mainly with the later "eyed egg" stages of development where the yolk is compact and the blood flow is copious. Being small and essentially transparent the egg clusters may pass unnoticed by the casual observer. The pale pink eggs blend in with encrusting pink algae. Virtually all egg masses observed on the shore had an adult T. capito in attendance. On several occasions 2-3 adults were found close to the eggs. The male T. capito found with the eggs kept at the laboratory remained close to the eggs, moving from side to side and fanning the pectoral fins to create a current of water. This constant circulation apparently ensures a supply of oxygenated water to the eggs and helps in the removal of detritus that may otherwise attach to the egg surface.

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Development of the Egg and Prolarva

The egg is essentially spherical although slightly dorsoventrally depressed. The flattened base is covered with numerous fine, translucent, adhesive threads. The mean chorion diameter is 1.07mm (100 eggs measured) and ranges from 1.00mm - 1.10mm. Early in development the yolk is spherical and averages 0.90mm and contains 80-120 small oil globules closely associated with 20-25 pigment spheres. No cluster was found with eggs earlier than the blastula stage and these were estimated to be about thirty hours old. Development to hatching (Fig. 1, Nos. 1-9) took 17 days at a temperature ranging from 11°C-13.5°C.

Thirty hours (Fig. 1, No. 1). The blastula is well formed and consists of a rounded cap of cells (blastoderm) overlying a deep blastocoel. Pigment spheres and associated oil droplets are distributed evenly throughout the yolk.

Second day (Fig. 1, No. 2). The blastodisc has spread half way around the yolk. The embryonic shield is poorly defined, appearing only as a thickened portion of the blastodisc.

Third day (Fig. 1, No. 3). The blastopore has closed. The optic vesicles are present but rudimentary. The embryo is deeply notched into the yolk, particularly in the head region, and the tail bud is flat. Several of the yolk pigment spheres have coalesced, as have some of the oil globules, effectively reducing slightly the number of each.

Fifth day (Fig. 1, No. 4). The pericardial cavity is well defined and the heart beats faintly, but there is no visible blood circulation. The brain is lobed and the ventricles pronounced. A cluster of small stellate melanophores lies anterior and posterior to each eye; the greatest number lie posterior to the eyes. The chorioid fissure is not closed. The auditory placodes appear as two small rings lateral to the hind brain. Behind each placode there is a group of about 10 small melanophores. Two more pigment clusters lie half way along the embryo, and several scattered melanophores are present in the tail bud. Pigment spheres and oil globules continue to coalesce.

Sixth day (Fig. 1, No. 5). The heart beats strongly and rapid circulation is visible in the dorsal and ventral blood vessels and the vitelline tributaries. Brain lobes have expanded laterally, especially the mesencephalon, and two otoliths are present within the otic vesicles. The tail extends well clear of the yolk and the gut is long and tubular. Several stellate melanophores surround the gut and extend in two rows along the ventral aspect of the tail. These melanophores are obscure and cannot be accurately counted. Ten to 15 stellate melanophores lie scattered over the yolk surface. Twenty to 30 oil droplets and 3-4 pigment spheres remain within the yolk. The relative position of the oil globules in the yolk varies according to the attitude of the egg because the oil floats to the uppermost portion of the yolk.

Eighth day (Fig. 1, No. 6). The heart now lies slightly forward of the head. The chorioid fissure has closed and eye pigmentation is just visible. The general arrangement of the body pigment has altered very little. A large pigment patch is present at the posterior end of the gut, and a single row of 5 stellate melanophores runs along the ventral midline of the tail. Beginning directly above the anus 6 stellate melanophores run along the dorsal mid-line of the tail. Several melanophores are visible above the hind portion of the mesencephalon. All pigment spheres have disappeared from within the yolk. The tubular gut is longer.

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Tenth day (Fig. 1, No. 7). The mesencephalon has expanded dorsally. The chorioid pigmentation is extensive although the lenses are still visible through it. The number of scattered melanophores present anterior and posterior to the eyes, above the gut and laterally within the tail is reduced. Two are present above the brain and 4 behind each otic vesicle. The melanophores along the dorsal mid-line are reduced to 3 or 4 while those on the ventral mid-line have increased to 11 or 12. Rudimentary pectoral buds and fin folds are visible.

Twelfth day (Fig. 1, No. 8). A further reduction in the number of melanophores above the gut, over the yolk surface, and anterior and posterior to the eyes has taken place. Those melanophores situated around the eyes adhere closely to the back of the eye and are somewhat obscured by the chorioid pigment. One or two melanophores lie along the lateral aspect of the body directly behind each pectoral bud.

Fourteenth day (Fig. 1, No. 9). The yolk is considerably reduced, more dense and contains a single large oil globule and 13-15 smaller ones. The head is raised from the yolk revealing the chambers of the heart and the lower jaw. Pigmentation of the chorioid appears complete with many iridiophores present. The amount of body pigmentation varies. Many individuals have only those melanophores found above the gut and along the mid-ventral and mid-dorsal lines. Other specimens still possess the clusters behind each otic capsule and the 8 melanophores around the base of the brain and between the eyes. The mouth, external nares, pectoral fins and fin folds are well formed. By the 16th day (hatching) there is no pigment beneath the brain or behind the otic capsules. Just before hatching the embryo turns violently within the egg at frequent intervals. Eventually the tail penetrates the chorion, freeing the new prolarva.

Prolarva (Fig. 1, Nos. 10 and 11). Prolarval length on hatching ranges from 4.50mm - 5.25mm s.l. The amount of yolk present varies, being influenced by the degree of premature hatching caused by disturbance of the egg, such as by changing the water. The gut is long and convoluted. Above the gut, within the peritoneal layer, are two large melanophores, one directly anterior to the vent and the other above the hind portion of the liver. Some specimens also possess a melanophore beneath the gut and slightly anterior to the vent. The reduced yolk is bordered anteriorly by the heart and posteriorly by the liver and prominent green gallbladder. Sixteen to 26 (most commonly 21) stellate melanophores are present along the ventral mid-line behind the anus. Two to 5 dorsal melanophores are present in the tail. Two stellate pigment spots are situated either side of the anterior part of the yolk. An occasional specimen was found in which the melanophores around the brain and eyes and behind the otic capsules were still present, but these melanophores rapidly faded.

Spawning and Development of T. Robustum

In the Lyall Bay and Island Bay areas T. robustum spawns from early July to late October. Egg masses are found throughout the tidal zone beneath stones, broken clay pipes, sheets of asbestos and Haliotis shells. Egg clusters appear most abundant about the upper mid-tide level although many are found further up the tide, sometimes completely out of the water for several hours during low tides. Several egg clusters were found in oyster shells located in spat collecting trays that were suspended from rafts 20 feet above the nearest portion of rocky seabed. page 5The size of the masses range from 5cm in diameter, with 1-2 hundred eggs, to about 12cm in diameter with several thousand eggs. The eggs are laid close together forming flat irregularly arranged clusters.

The large egg masses contain groups of eggs at different stages of development, suggesting that like T. capito, these clusters are the result of several different spawnings. The eggs are essentially colourless although collectively they appear pale green. The colour of the yolk (pale yellow) changes very little as development proceeds. Five separate egg masses were laid in the asbestos aquarium and in each case the male parent attended the eggs. The male T. robustum, like the parent T. capito, lay close to the eggs and created a current of water by movement of its anal and pectoral fins. Again this ensured a supply of oxygenated water and the removal of detritus. Egg masses kept without a male parent or adequate aeration suffered up to 90% mortality. These eggs also accumulated masses of minute debris which covered the entire chorion and obscured the embryo.

Development of the Egg and Prolarva

The egg and yolk are completely spherical, and the mean chorion diameter of 80 eggs was 1.16mm (range 1.12-1.23mm). The yolk early in development is slightly granular, and contains 25-35 medium sized oil droplets closely associated with 15-25 pigment spheres. The eggs attach to the substrate by a mass of tendrils arising from one side of each egg. Each tendril consists of a matted series of fine filaments that arise from a single point on the chorion. These tendrils are larger than those of T. capito.

Development to hatching (Fig. 2. Nos. 1-12) took 22 days at a water temperature ranging from 11°C-13.5°C.

Two hours (Fig. 2. No. 1). A single large mass of protoplasm appears at one end of the yolk.

Fifteen hours (Fig. 2, No. 2). One hundred and twenty-eight angular cells form a low cap on one side of the yolk.

Thirty hours (Fig. 2, No. 3). The blastula is well formed and consists of a semi-circular mass of cells (blastoderm) overlying a wide blastocoel.

Fifty hours (Fig. 2, No. 4). The blastodisc covers two-thirds of the yolk. The embryonic shield is clearly defined and lies slightly embedded in the yolk, particularly in the anterior region.

Third day (Fig. 2, No. 5). The embryonic axis (neural keel and somite precursors) is obvious although still flattened against the yolk. Poorly defined optic vesicles are visible. Twelve to 20 large oil globules are present and the pigment spots have decreased in number (to 5-10). The blastopore is closed.

Fourth day (Fig. 2, No. 6). The embryo is prominent above the yolk surface and encircles more than half of the yolk sac. The lenses are formed and have partially separated from the ectoderm. Eight myomeres lie well forward either side and Kupffer's vesicle has appeared directly beneath the tail bud. A group of tiny melanophores lies anterior and posterior to each eye. A further two clusters are laterally positioned within the myomeres half-way along the embryo.

Fifth day (Fig. 2, No. 7). The brain is lobed and the ventricles are visible. The auditory placodes appear as faint depressions behind the eyes. Approximately 15 stellate melanophores lie scattered over the page 6surface of the yolk sac. The relative position of the melanophores is unchanged although there is an increase in the chromatophore number. A further group of melanophores has developed behind each otic vesicle.

Sixth day (Fig. 2, No. 8). The heart beats slowly and faintly but no blood flow is visible except very close to the heart. The pericardial cavity has not yet expanded and the heart is embedded in the yolk directly beneath the head. The chorioid fissure has not closed. Each auditory placode appears as a double ringed structure. Four pairs of chromatophore groups are present, with one group anterior and another posterior to each eye, one behind each auditory placode and one two-thirds back along the body of the embryo. The melanophores in these groups form a diffuse network making accurate counting impossible. The tail bud is still attached firmly to the yolk surface.

Seventh day. The heart beats regularly and strongly, and blood flows through the main vessels and across the yolk tributaries. The heart lies deep within the pericardial cavity slightly forward of the head. The sinus venosus is the only clearly visible chamber. The oil globules are reduced further (to 5-10), and all pigment spheres deep in the yolk have dispersed. The anterior myomeres are chevron shaped.

Eighth day. The yolk is dense and granular. The embryo alters position about once every minute.

Eleventh day (Fig. 2, No. 9). Pigmentation has appeared in the chorioid of the eye and the chorioid fissure has closed. The eyes have shifted laterally broadening the head and bringing the otic vesicles closer to the eyes. Several stellate melanophores are scattered above the brain and along the mid-ventral and mid-lateral aspects of the body and tail. The tail overlaps the head and the rudimentary pectoral buds are present.

Thirteenth day (Fig. 2, No. 10). Three otoliths lie within each otic vesicle. The chorioid pigment is darker although with transmitted light the lenses are still visible. Individual melanophores throughout the embryo are generally larger, although the size varies according to changes in light intensity. The melanophore clusters that were located two thirds back along the body have dispersed. Fewer pigment spots are present on the yolk surface. There is a large melanophore in the upper peritoneum slightly forward of the anus and 8 smaller ones above the gut in the region of the pectoral fins. The tail is long and passes over the head and returns to lie parallel with the body. Narrow fin folds are visible.

Sevententh day (Fig. 2, No. 11). The head is lifted slightly from the yolk, exposing the chambers of the heart and the poorly developed lower jaw. The lenses are no longer visible through the eye pigmentation. The gallbladder is visible in the mid-gut region. Two to 8 oil globules are present within the yolk.

Twentieth day. The external nares appear as two shallow depressions anterior to the telencephalon. A row of 9-10 stellate melanophores runs along the mid-ventral line past the vent. Fin folds and pectoral fin buds are well developed.

Twenty-second day (Fig. 2, No. 12). The yolk is reduced considerably and the ventral side of the embryo faces upwards. Numerous iridiophores are present in the chorioid of the eye. A considerable reduction in the amount of pigment present around the brain, above page 7the gut and in the lateral mid-line of the tail has taken place. Two to 3 chromatophores lie on the yolk surface. The mouth, external nares and pectoral fins are well defined. The embryo twists violently before hatching. The tail is flexed rapidly, as a result of which the chorion is ruptured and the prolarva is released. Immediately following this release the prolarva swims to the surface.

Prolarva (Fig. 3, Nos. 1 and 2). Prolarval length on hatching ranges from 5.70mm-6.10mm s.l. All melanophores about the brain have faded. As with T. capito the size of the yolk sac varies according to the degree of premature hatching. Three to 4 oil globules are present in the yolk. The upper gut peritoneum has two large melanophores, one slightly behind the yolk and the other slightly anterior to the anus. The yolk is bordered anteriorly by the heart and posteriorly by the liver and the prominent gallbladder. From 5-15 stellate melanophores are present along the ventral mid-line behind the anus and from 2-4 are situated along the dorsal mid-line of the tail. One or two melanophores lie beneath the pectoral fins on either side of the yolk. The prolarvae are positively phototropic.