ON THE EGGS, REARING, HABITS OF THE FRY, AND GROWTH OF SOME CEPHALOPODA SANG CHOE Biology Division, Atomic Energy Research Institute, Seoul, Republic of Korea ABSTRACT Eggs of Sepia esculenta, S. subaculeata, Sepiella maindroni, Sepioteuthis lessoniana, and Euprymna berryi were hatched in concrete cisterns. The fry were fed live and dead invertebrates and fishes and were raised to near-adult sizes. Live mysids appeared to be a favored food. Details of the culture methods are given and observations noted on behavior and growth of each species. INTRODUCTION There is a diversity of literature on the Cephalopoda, the most highly evolved of the invertebrates. Major works of importance to this paper include those by Naef (1923, 1928), Robson (1929, 1932), Sasaki (1929), and Voss (1956). There are about 650 known species of Cephalo- poda, but few of them have been studied as to life history or ecology. Knowledge of the life history of the various species would be of great value to the fields of taxonomy, phylogeny, and evolutionary theory. Many species of Cephalopoda are among the most desired and costly food items in the Orient, although they are seldom used for food in the West. These species are of great interest from a commercial, as well as purely biological, viewpoint. Four of the species discussed here, Sepia esculenta, S. subaculeata, Sepiella maindroni, and Sepioteuthis lessoniana, are as important as the octopus among Japanese fisheries products. For this reason, the author has engaged in experiments on the rearing of these four species and the smaller Euprymna berryi. It should be emphasized here that production of fry in large quantities is as important an aspect as control of reproduction and perfection of rearing techniques. All of the above mentioned species can be reared satisfactorily, under favorable conditions and with the proper food supply, and can be supplied in large quantities as fry. Growth experiments with these fry have given extremely favorable results, indicating a strong probability of success on an industrial scale. Reported in this paper are the spawning season, the form of the eggs, resistance of the egg and hatched fry to low salinity, the method of rearing, the characteristic behavior of fry, and growth. I am grateful to Dr. Y. Ohshima, University of Tokyo, and Dr. N. Nakamura, Director of Japan Freshwater Fisheries Research Laboratory for their manifold help throughout the work. I also express special thanks 1966) Choe: Rearing Cephalopods 331 22 -u ~20 GI 5 18 -o ; 16 D. ~ 14 -•. 12 / ~ ~ ~ 10 ______0/~--- March April May June July Spawning season FlGURE 1. The relation between the spawning season and water temperature. The water temperature represents a mean for the period from 1953 to 1957, at 10m depth in the main spawning ground of Atsumi, Aichi Prefecture. S.e., Sepia esculenta; S.s., S. subaculeata; S.m., Sepiella maindroni; E.b., Euprymna berryi; S.I., Sepioteuthis lessoniana. to Dr. G. L. Voss and Mr. E. McSweeney, Institute of Marine Science, University of Miami, for reading the manuscript and offering construc- tive help. MATERIAL AND METHODS Eggs used for the Sepia esculenta, S. subaculeata, and Sepiella maindroni experiments were those spawned on the egg-collectors made of bundles of azalea twigs, which had been sunk on the bottom on the spawning ground. In the case of Sepioteuthis lessoniana and Euprymna berryi, eggs spawned on the spawning ground were collected and used. Newly hatched fry were reared and cared for in two concrete cisterns of 167 cm X 167 cm x 50 cm and 335 cm X 335 cm X 90 cm, with flowing water. All the fry were fed primarily with the mysid Neomysis japonica Nakazawa until 20 to 40 days after hatching. Later, as they grew, they were given live shrimp (Palaemon nipponensis de Haan and Leander serrifer Stimpson), live, young, small fishes (primarily gobies) and, as a dead prey, anchovies. SPAWNING SEASON There are reports on the spawning season of Sepia esculenta by Yamamoto (1942a), Yasuda (1951), Koito et al. (1956), and Tomiyama 332 Bulletin of Marine Science [16(2) FIGURE 2. The eggs of Sepia esculenta. (1957); of Sepiella maindroni, by Yamamoto (1942b), and Koito et al. (1956); of Sepioteuthis lessoniana, by Choe & Ohshima (1961); of Euprymna berryi, by Maekawa (1961). The relation between the spawning season and the water temperature, observed for these species at Atsumi Bay, Aichi Prefecture, is shown in Figure 1. They move into the bay in spring for spawning, and the spawning lasts till the early summer. Habitually, Sepia esculenta, S. subaculeata, and Sepiella maindroni spawn on twig-like bodies on the muddy or sandy sea bed at an average depth of 10m. Slender twigs of trees or bamboo, stationary netting, annelid tubes, or Zostera marina (eel grass) make good material for the eggs to cling to. Sepioteuthis lessoniana, on the other hand, spawns its eggs in a lump on pebbles, broken pieces of shell, Chorda filum, etc., on the pebbly sea bed at a depth of 2 to 10m, while Euprymna berryi usually spawns on the stems of Zostera marina. The water temperature at spawning is 100-200e for Sepioteuthis lessoniana, and 17°-21 °e for Euprymna berryi. EGGS Sepia esculenta.-Freshly spawned eggs are enclosed in a milky-white, 1966] Choe: Rearing Cephalopods 333 FIGURE 3. The eggs of Sepia suhaculeata. soft, gelatinous substance. The surface of the egg capsule is coarse, and on it can be seen four faintly protuberant lines which converge towards the tip. On either side of the protuberant lines traces of suckers are recognizable. The major axis is 16-21 mm long, and the minor axis 12-14 mm long (Yamamoto, 1942a). Eggs are spawned separately on the object chosen. In many cases, the surface of the egg capsule becomes darkly discolored with adhering sediment particles within two or three days after spawning (Fig. 2). Sepia subaculeata.-The eggs are enclosed in a milky-white, soft gelatinous substance, the capsules being larger and comparatively more slender than those of S. esculenta. The surface of the egg capsule is coarse; on it can be seen three to four faintly protuberant lines which spiral slightly counter- clockwise from the base of the egg capsule toward the tip. The capsules have a major axis of 27-34 mm (31.5 mm average) and a minor axis of 14-16 mm (14.7 mm average), and the individual egg is intertwined with and connected to the base through the egg stalk. Sediment particles often coat the surface, coloring it a muddy black (Fig. 3). Sepiella maindroni.-The egg is coated with much elastic, dark-brown, gelatinous substance, and measures, according to Lin (1935), 6.0-6.5 mm 334 Bulletin of Marine Science [16(2) FIGURE 4. The eggs of Sepiella maindroni. long on the minor axis, or, according to Yamamoto (l942b), 7.5-10.5 mm on the major axis and 6.5-8.5 mm on the minor axis. The surface of the egg capsule is smooth, with no protuberant lines and usually with no adhering sediment particles (Fig. 4). Sepioteuthis lessoniana.-The eggs are embedded in a milky-white, semi- transparent, soft gelatinous substance, and the capsules are long and slender, each capsule containing 2-9 eggs in a row (5.8 eggs average) (Choe & Ohshima, 1961). The egg capsule is 62-84 mm (76 mm average) in length, with a maximum breadth of 9-13 mm (11 mm average). The surface of the egg capsule is smooth and no sediment particles adhere to it (Fig. 5). Euprymna berryi.-The egg is heavily coated with milky-white elastic gelatinous substance, and presents a circular form, though the front end of the egg capsule projects slightly. The egg capsule is 5.2-7.7 mm (6.3 mm average) on the major axis and 4.7-5.7 mm (5.2 mm average) on the minor axis, and the surface is coarse, with irregular, faintly protuberant lines. No sediment particles adhere to it. Cephalopod eggs initially pass through a process of contraction and 1966] Choe: Rearing Cephalopods 335 FIGURE 5. The eggs of Sepioteuthis lessoniana. then increase in size again with the developing embryo and perivitelline space, reaching the maximum size just before hatching (Lin, 1935; Yamamoto, 1941, 1942a, 1942b; Choe & Ohshima, 1961). This phenomenon is typical of the egg of Sepia subaculeata; Figure 6 shows the change in size of the egg capsule during the egg development. The egg of Sepia subaculeata shows a variation of about 39 per cent for the major axis and about 50 per cent for the minor axis from its most contracted stage. For this reason, when giving a morphologic description of the eggs, size must always be correlated with age. RESISTANCE OF THE EGG AND NEWLY HATCHED FRY TO Low SALINITY The first problem in obtaining healthy fry is the care of the eggs. As cephalopod eggs usually require a fairly long time to hatch, they are liable to be subjected to some variation in the environment. Their limitations in this respect must be considered when setting up an artificial environment. The length of time required for hatching varies greatly with water temperature for the species considered here. It is reported that Sepia esculenta requires 55-86 days to hatch at 12.3°-21.9°C or 29-42 days at 15.5°-23.6°C (Yamamoto, 1942a); Sepiella maindroni requires 336 Bulletin of Marine Science [16(2) TABLE 1 PERCENTAGE OF EGGS HATCHED AT VARIOUS SALINITIES ------ Chlorinity Sepia Sepie/la Sepioteulhis (%0) esculenta maindroni lessoniana 8.4 0 0 0 10.5 0 18.8 0 12.6 46.1 37.5 9.0 13.1 10.6 14.7 65.5 50.0 22.5 15.8 25.0 16.8 57.7 62.5 47.6 28-30 days at 20°-26°C (Lin, 1935); or 35-53 days at 14.7°-23.2°C (Yamamoto, 1942b).