T A N E 28,1982

E A R L Y L I F E H I S T O R Y O F C A P T I V E - R E A R E D GOBIOMORPHUS BASALIS (OSTEICHTHYES: E L E O T R I D A E )

by David J . Riddell

Gordonton Road, R.D.I., Taupiri

S U M M A R Y A method for rrearing Cran's bully (Gobiomorphus basalis) in captivity

is outlined. The development of this species throughout the first four weeks after hatching is described, with illustrations. Cran's bully is seen to be more advanced at hatching than related species, though the rapid development observed may be due to artificial factors such as the temperature at which the aquarium was kept and the ready availability of food.

INTRODUCTION

Cran's bully is a common, though poorly-known species of native freshwater fish found primarily in rocky, bush-clad streams throughout the North Island of New Zealand, but known also from lakes in the Gisborne area, and from tarns near Molesworth in the South Island (McDowall 1978). It also occurs in Western Springs, Auckland (personal observation). Little is known of the reproductive biology of this species except that the eggs are quite large, and the young remain in fresh­water, hiding in the shallows at the water's edge. Spawning behaviour has been described by L.W. Spooner (McDowall 1978) although no details of the subsequent development of the eggs are given.

M A T E R I A L S A N D M E T H O D S

Several specimens of Cran's bully, collected from Western Springs and the Waitakere Stream, together with several other species of native fresh-water fish were kept in an unheated aquarium measuring 1 240 x 440 x 440 mm. They were fed primarily on finely chopped earthworms, with occasional feedings of mosquito larvae, Daphnia, chopped beef or fish, and small Gambusia. In October 1981, one of the male bullies assumed nuptial coloration (totally black, except for a yellow-orange stripe along the top edge of the first dorsal fin) and began defending a small territory centred on a rock measuring approximately 220 x 150 x 100 mm, under which he spent considerable time. Eventually he was joined by a ripe female, who laid her eggs on the underside of the rock. Spawning itself was not observed. After seven days, during which the

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eggs were guarded by the male, the eggs, still attached to the rock, were removed to a bare aquarium measuring 890 x 380 x 460 mm. A n airstone was placed close to the eggs to provide some water movement and dead eggs were removed with forceps as they appeared. Despite these precautions, hatching, which occurred 16 days after spawning, was unsuccessful, and no young survived. Fouling of the egg surfaces by detritus and fungi appeared to be responsible.

A second batch of eggs, fathered by the same male, was laid about three weeks later. Again, spawning was not observed, and the eggs were well advanced in development before being detected. From experience with the first batch, however, it was decided that when the larval eyes had been silvery for three days, the eggs must have been close to hatching. They were therefore removed to the bare tank with an airstone as before. This time about 50 larvae hatched successfully, two days later on 21 November. Initially, the young fish were fed on a commercially prepared fry food in liquid suspension, supplemented by a suspension of ground hard-boiled egg yolk in water. However, they did not thrive on this diet, apparently because the food particles were too fine: one six-day old fish which was examined had an empty gut and had not grown beyond the three day stage. After seven days the fish were therefore fed twice a day on newly hatched brine shrimp (Artemia salina) on which they grew rapidly. After five weeks the fish were large enough to take small Daphnia and mosquito larvae, and these foods progressively replaced the brine shrimp. The water was changed periodically throughout this time to prevent fouling. Ten weeks after hatching, by which time the largest individuals were about 25 mm long, the surviving 40 fish were released into Western Springs or given away to fellow aquarists.

A t irregular intervals (1, 3, 13, 20 and 27 days after hatching), a fish was removed, anaesthetised in a 1% solution of poly phenyl phenoxytone glycol and drawn with the aid of a binocular microscope. The fish could not be revived afterwards.

R E S U L T S

1 Day (Fig. 1) The newly hatched fish are relatively large (5.7 mm TL) with small

yolk sacs, and are able to swim, albeit weakly. Median fin folds extend along the posterior two thirds of the dorsal and ventral surfaces. The fin rays of the anal and second dorsal fins are scarcely apparent, although those of the rounded caudal fin are well-developed. Pelvic and first dorsal fins are absent. Only 25 neural spines could be discerned. A series of chromatophores extends along the ventral surface of the tail to the anus, and from there along the dorsal surface of the gut and swim bladder. A few more are found ventrally on the gut and yolk sac.

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Fig. 1 G. basalis, one day old. Scale bar on this and successive figures is 6 mm.

Fig. 2. G. basalis, three days old.

Fig. 3. G. basalis, thirteen days old.

Fig. 4. G. basalis, twenty days old.

Fig. 5. G. basalis, twenty-seven days old. 209

3 Days (Fig. 2) Already many of the juvenile characteristics are becoming less

pronounced. The fish have virtually lost their yolk sacs, started feeding, and can now swim quite actively. The fin folds are of much lesser extent, the anal and second dorsal fins are more clearly defined, and the tail is squarer. The neural spines are all present (29 - 30) though only 12 of the adult's 15 - 17 haemal spines could be seen. The gills are now distinguishable. The chromatophores on the ventral surface of the viscera have disappeared, but more have developed along the back from the anterior end of the dorsal fin almost as far posteriorly as the tail, and several are present over the lateral and dorsal surfaces of the brain. 13 Days (Fig. 3)

The anal and second dorsal fins are now well-defined, and the haemal spines are all present. The chromatophores over the intestine have been lost, although those on the swim bladder are retained. The postero-dorsal chromatophores are more scattered. 20 Days (Fig. 4)

After 18 days, the first dorsal fin and pelvic fins begin to appear on the largest individuals (by now the fish show a considerable size range). The other main development occurring at about this time is the constriction of the notochord into distinct vertebrae. The dorsal chromatophores become aggregated into patches, with further patches developing laterally, foreshadowing the colour pattern of the adults. 27 Days (Fig. 5)

Now measuring about 13.5 mm, the young fish are easily identifiable as small bullies. The largest individuals have become negatively buoyant after 24 days (although they still possess a fair-sized swim bladder), and the viscera have become opaque and more clearly defined: to mask this the abdomen has become distinctly silvery. The chromatophores are arranged in distinct patches dorsally, laterally, and ventrally. Numerous chromatophores darken the nerve cord and the dorsal and lateral surfaces of the brain. The fins are fully developed.

DISCUSSION

The development of the young fish observed in this study was remarkably rapid. The closely related upland bully (G. breviceps) has a mean time to hatching of 33 days in October at a mean temperature of 14.4°C but only 24 days in November at a mean temperature of 17.5°C (Staples 1975). McDowall (1965) also found that hatching time of the red-finned bully (G. huttoni) depended on temperature. The very short time taken to hatching in the present study (16 days) is therefore probably due to the high temperatures' (mean approximately 21°C) maintained in an indoor aquarium. Likewise the shorter time taken to acquire benthic habits (one month rather than six as in Staples' study),

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is probably due largely to the warm temperatures, although another possible factor contributing to this rapid growth was the ready availability of suitable food: periodic shortages of food in the wild could result in temporary cessation of growth, as was observed in the present study between days 3 and 6, when food was scarce.

The Cran's bully does, however, seem to be more advanced at hatching than the upland bully, which has a mean length within two days of hatching of 5.05 mm, and takes eight days to develop dorsal and anal fin rays and lose the yolk sac (Staples 1975). The young of the red-finned bully, which wash out to sea immediately after hatching (McDowall 1978) are even less developed at hatching. McDowall (1965) has illustrated a newly hatched larva 2.7 mm long, with a very large yolk sac, as well as a nine-day old laboratory-reared individual. He was unable to rear the fish beyond this stage, and nothing more is known of the development of the juveniles until they re-enter fresh-water. McDowall (1972) has illustrated this stage, and the corresponding stage of the blue-gilled bully (G. hubbsi), another diadromous species.

A C K N O W L E D G E M E N T S

I would like to thank Ian Southey for his assistance with the rearing of the fish, and Annette Taylor for typing the manuscript.

R E F E R E N C E S

McDowall, R.M. 1965: Studies on the biology of the red-finned bully Gobiomorphus huttoni (Ogilby). Part II. Breeding and life history. Transactions of the Royal Society of New Zealand 5(14): 177-196.

McDowall, R.M. 1972: What's in that whitebait net? New Zealand Marine Department Fisheries Information Leaflet 3:1-9.

McDowall, R.M. 1978: "New Zealand Freshwater Fishes: a Guide and Natural History". Heinemann Educational Books (NZ) Ltd., Auckland. 230 p.

Staples, D .J . 1975: Production biology of the upland bully Philypnodon breviceps Stokell in a small New Zealand Lake. I. Life history, food, feeding and activity rhythms. Journal of Fish Biology 7(1): 1-24.

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