Egg Laying and Egg Mass Nursing Behaviour in the Japanese Mantis Shrimp*1
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Bulletin of the Japanese Society of Scientific Fisheries 50(12), 1969-1973 (1984) Egg Laying and Egg Mass Nursing Behaviour in the Japanese Mantis Shrimp*1 Tatsuo HAMANO*2 and Shuhei MATSUURA*2 (Accepted December 5, 1983) The spawning and egg mass nursing behaviour, together with the change in external appearance of the egg mass, of the mud-dwelling Japanese mantis shrimp Oratosquilla oratoria were studied using artificial burrows in aquaria. This species usually spawns in a supine posture in the burrow maintaining this posture with the back of abdomen and exopods of uropods against the wall of burrow for almost 3 h. The newly extruded egg mass is amorphous, but the female shrimp compacts it and then shapes it into a thick disc within 1 h and to a thin disc having a marginal turnup within 24 h of spawning. All maxillipeds excluding the raptorial claw are used for the nursing behaviour, i.e. spreading and folding the egg mass, so it is teased out and becomes a tuft shape after 3 days or so. The second egg laying occurred in 2 females about 40 days after the first spawning of each individual at 25•Ž, and this fact suggests that O. oratoria may spawn more than once in a spawn ing season in natural warm waters. The Japanese mantis shrimp Oratosquilla ora mm in diameter and 600 mm in length,8) on the toria (DE HAAN) lives in burrows in the mud bot grit bed at the Fishery Research Laboratory of tom of bays and inlets. Although this species is Kyushu University, Tsuyazaki (Fig. 1). Six ani much used for edible meat in Japan, there is no mals in the first catch were reared in flowing, fresh detailed report of its behaviour. seawater where the temperature fell to 11.0•Ž in With many species of other crustacean orders, January, 1983 under natural photoperiod until the egg laying behaviour has been studied in detail. February 5 in 1983, and then the water tempera In Stomatopoda, however, an account of spawning ture was raised to 25•Ž and photoperiod was fixed behaviour has not been published notwithstanding at 15L9D. In addition, the 37 individuals from the known behaviour nursing the egg mass1-4) and the second catch were reared under natural sea embryonic development.1,5 water conditions and the temperature reached ) The present authors induced egg laying of the 30.2•Ž in August from 16.2•Ž in April, 1983. mantis shrimp by rearing in artificial burrows which made observation in aquarium of the be haviour of mud-dwelling mantis shrimp possible.8) The present paper contains the first description of spawning behaviour in Stomatopoda and detailed observations of nursing in relation to change in external appearance of the egg mass of the mantis shrimp. Materials and Methods Adult female mantis shrimps, more than 30mm in carapace length, were captured with a tow net in the waters of Hakata Bay, firstly 6 animals on September 28, 1982 and secondly 37 on April 26, Fig. 1. Aquarium arrayed in artificial burrows for 1983. They were kept in large aquaria, 102 x rearing of mantis shrimp. Rod on the right is 103x114cm, provided with artificial burrows, 56 an electric thermometer sensor. *1 Ecological Studies on the Japanese Mantis Shrimp, Oratosquilla oratorio (DE HAAN)-‡U. *2 Department of Fisheries, Faculty of Agriculture, Kyushu University 46-04, Hakozaki, Higashi, Fuku oka 812, Japan (ûM–ì—´•v•E•¼‰Y•C•½:‹ã•B‘åŠw”_Šw•”). 1970 HAMANO and MATSUURA Fig. 2. Diagrammatic lateral view of mantis shrimp O. oratoria illustrating terms used in descrip tions. Mantis shrimps were fed with short-necked clam, from the genital openings at the centre, ventrally krill and sardine. The mature ovary of mantis of the sixth somite, being linked each other by an shrimp can be seen through the ventral face of adhesive substance forming a string (Fig. 5). Then telson, so its shape was observed periodically to the eggs formed an adhesive mass of uncertain detect the degree of ovarian development. shape (Figs. 5 and 6-1) which dangled from the Terms used in this text are shown in Fig. 2, and edge of thoracic somites since during the progress size measurement follows MATSUURA and HAMA of egg extrusion the body always leaned to one NO. 8) side (Fig. 4-1). The animal kept this inclined posture, scarcely moving excepting the pleopods, Results until the end of spawning. The time required for egg laying was an average of 167 min for 5 spawn The Japanese mantis shrimp never laid eggs out ings; ranging from 125 to 217 min. of the artificial burrow. The shrimp always The female stretched her body out straight in the spawned within a week after the ovarian shape on supine posture after spawning, and then she form the ventral side of telson had assumed the shape of ed the egg mass compacting it by rotation of all an isoceles triangle (Fig. 3). the maxillipeds excluding the second, raptorial Egg laying took place in all of the 6 females claw. This compacting behaviour usually con reared in warmed water during the period from tinued for a quarter hour or so, to give the egg April 17 to June 1 in 1983 and in 22 of the 37 mass a globe shape. Following this compaction, females reared under natural water temperatures shaping behaviour was observed; the mantis shrimp during the period from May 14 to July 8 in 1983. alternately stretched and rotated the egg mass The Mann-Whitney U test showed that heated with the right and left portions of the meri to the water significantly promoted ovarian maturation in this species (U=5, P<0.001). Mantis shrimp started laying eggs during daylight hours in 15 of the 19 spawnings observed in aquaria. The entire process of egg laying was clearly observed in 5 cases and the spawning posture was observed in 11 cases. The female adopted a supine posture, firmly supporting the body on the inner wall of the bur row using dorsal portions of the first to the fourth abdominal somites and both exopods of uropods (Fig. 4). The pleopods were slightly elevated, but other parts, antennae, maxillipeds and pereopods, remained at rest, Animal intermittently adopted Fig. 3. Ventral surface of telson of well matured fe this posture for several hours before spawning. male of 0. oratoria. Arrow represents ovary Eggs were freely extruded onto the thoracic somites site. Scale 1 mm. Egg Laying Behaviour in Mantis Shrimp 1971 Fig. 4. Egg laying posture of mantis shrimp in artificial burrow . View from front (1) and view from behind (2). Identifying number is drawn on telson (2) . a: egg mass, b: the second maxilliped, c: the fifth maxilliped, d: the sixth abdominal somite, e: exopod of uropods. Fig. 5. Lateral view of spawning posture of mantis shrimp, which was forcibly removed out of burrow to take photos during egg laving. Arrow represents egg mass. dactyli of the third to the fifth maxillipeds, so the was teased out by the maxillipeds and came to re egg mass was given a shape similar to a thick disc semble a tuft after 3 days or so, succeeding to within about I h after spawning (Fig. 6-2). Sub spawning (Fig. 6-4). At first, spawned female sequently the female continued shaping the egg always kept the egg mass with devoting almost half mass until it became a thin disc having a marginal of her time to nursing it; feeding occurred rarely turnup, about 10 cm in diameter, which was only and at times of emergence from the burrow the slightly adhesive (Fig. 6-3). The egg mass was egg mass was carried by the maxillipeds though usually given this form within 24 h after spawning. emergence seldom occurred. Finally, just before Then the animal commenced to nurse the egg mass, hatching, the female tended to neglect the egg mass which was alternately advanced and retracted or to a large extent, i.e. by laying it down in the bur spread and folded with the maxillipeds excluding row, to feed more frequently and by emerging, leav the second (Fig. 7). This nursing behaviour was ing it in the burrow, and not necessarily returning. continued until hatching though the frequency was However, any abandoned egg masses were eaten decreased gradually, and, therefore, the egg mass by other individuals, or became addled and never 1972 HAMANO and MATSUURA Fig. 6. Reshaping of egg mass of mantis shrimp. Undefined shape during spawning at the same time as Fig. 5 (1), thick disc shape at 1 h following spawning (2), thin disc shape having marginal turnup at 28 h (3), tuft shape at 3 days later (4). Scale 1 mm. sparent. Two females which lost the egg mass during the nursing period then resumed feeding and rapid ovarian development again and the second egg laying occurred about 40 days at 25•Ž after the first spawning. On May 16, 1983 one female showed a different spawning sequence and posture, which was very similar to the usual compacting behaviour but dif fered in the extrusion of eggs. The female ap peared to extrude the eggs directly into a shape similar to a ball of knitting yarn while in a standing posture and this egg laying accompanied with egg compaction was continued for 22 min after the Fig. 7. Egg mass nursing behaviour of mantis shrimp. present authors chanced upon it. The egg mass was eventually shaped into a thick disc shape (Fig. Arabic numerals represent orders of maxillipeds. 6-2) in only 13 min and the compacting behaviour developed.