Spawning Behavior and Early Life History of the Porcupine Puffer, Diodon holacanthus, in Aquaria

Abstract

The porcupine puffer, Diodon holacanthus Linnaeus, a well-known fish belonging to the family Diodontidae, inhabits the warm seas all over the world.However, both the behavior and life history of the puffer and its allies are virtually unknown.The present paper deals with the spawning behavior and the early life history of D.holacanthus based on observations at the Kanazawa Aqua-rium and the Marine Science Museum of Tokai University, from 1969 to 1975.
Spawning and reproduction of the puffer was first observed at the end of May when the water temperature reached approximately 24.4°C, and was observed continuously until the end of August.The parental fishes, measuring 176-259 mm (in males) and 210-231 mm (in females) in total length, were reared for one or two years since they were collected from the coasts of Wakasa Bay and Noto Peninsula, the Sea of Japan (Fig.2, Table 1).
Every day during the spawning season, in the afternoon or early evening, one or two males approach a female who remains motionless at the bottom of the rearing tank.The males, pressing their snouts against the belly of the female, incite her with their courtship behavior.The female is then slowly pushed upward towards the surface of the water by the males.Several other males also gather around the female and help to push her upward.If the female is not ready to spawn, she deserts the males and returns to the bottom alone.After repetition of such activities, the female spawns her eggs just below the surface of the water.And the eggs are fertilized simul-taneously by the males (Fig.1).Spawning always takes place between one female and four or five males with no exception, and occurs between 20: 52 and 23: 25 or at night at an undetermined time (Table 1).
The fertilized eggs of D.holacanthus are buoyant, colorless, and spherical, measuring 1.62-1.86 mm in diameter.During egg development, a thick external membrane appears over the yolk of the eggs 45 hrs.after fertilization.The hatching takes place 103-118 hrs.after fertilization when the water temperature is 24.2-25.5°C.The newly hatched larvae, measuring 2.46-2.73 mm in total length, have 12+8=20 myotomes and float belly upward just beneath the surface of the water.The larvae are covered with a thick pliable shell excluding the caudal section.Ten days after hatching, the larvae, measuring 4.86-5.94 mm in total length, form fin rays and several tuber-cles on the body.These tubercles contain the rudiments of the spine.The shell over the body becomes indistinct or disappears (Fig.3).
Thirteen days after hatching, small distinct spines can be observed in the tubercles.The fry, measuring 6.04-7.94 mm in total length, sometimes puff out their bellies.Twenty-five days after hatching, fused teeth and large irregular black speckles on the dorsal side are visible in fry measuring 20.3 mm in total length.Sixty-six days after hatching, the fry, measuring 46.5 mm in total length, have irregular speckles and pointed spines similar to those of the adult (Fig.4).
The thick external membrane and pliable shell, which can be observed from 45 hrs.after ferti-lization to 10 days after hatching in D.holacanthus, closely resembles the rudiment of the shell which appear in the similar stages of the trunkfish, Ostracion tuberculatus (see Mito, 1962) and of the slender mola, Ranzania laevis (see Leis, 1977).The characteristics of the eggs and larvae of D.holacanthus bear no resemblance to those of the known puffers (except the slender mola, R.laevis) belonging to the same suborder Tetraodontoidei, but rather resemble the trunkfishes belonging to the suborder Balistoidei.These results are thought to suggest to the systematic relationships between Ostraciontidae, Diodontidae, and Molidae.