FISHERIES SCIENCE 2000; 66: 1087–1091 Original Paper Growth and spawning of hatchery-reared Chinese white prawn Penaeus (Fenneropenaeus) chinensis released in the Ariake Sea, Japan Norihisa NAKASHIMA,1 Megumi MINAGAWA2,* AND Shiro ITO1 1Saga Prefectural Ariake Fisheries Research and Development Center, Ashikari, Saga 849-0313 and 2Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Ishigaki, Okinawa 907-0451, Japan SUMMARY: Growth and reproduction of hatchery-reared Chinese white prawn Penaeus chinensis released in the Ariake Sea, Japan, were examined. Chinese white prawn grew rapidly, reaching a body length of 154 mm in males and 198 mm in females by November (219–229 days after hatch- ing). Maximum body length of sampled individuals was 164 mm in males and 223 mm in females. Growth curve of the Chinese white prawn was fitted to the Pitcher and MacDonald’s formula, 2.925sin[2p(t - 16.151)/365] - 0.0623(t - 10.712) Lt = 155.0{1 - e } for males and the logistic curve, Lt = 200.3/[1 + (1.985–0.034t) e ] for females (where Lt is the body length t days after release and t is the number of days after release). Females reached sexual maturity in late February and spawning occurred until April. Minimum size at ripe and spawned stages was 189 mm and 193 mm body length, respectively. KEY WORDS: Ariake Sea, Chinese white prawn, growth, Penaeus chinensis, reproduction. INTRODUCTION Growth of the released juveniles has been examined by several prefectural fisheries experimental stations in Chinese white prawn Penaeus chinensis are mainly dis- Japan,5,6,10 but the relationship between growth and envi- tributed in the Sea of Pohai, Yellow Sea, and East China ronmental conditions is not well understood. Regarding Sea and form a major penaeid shrimp fishery in these reproduction of Chinese white prawn released to the areas.1,2 Growth and reproduction of Chinese white sea, females with spermatophore or recaptured mature prawn in these seas have been well examined.3 In Japan, individuals were only reported.4,5 Thus, for the Chinese Chinese white prawn are rarely observed in the wild, white prawn no detailed information on reproduction of but juvenile and adult Chinese white prawn have been released prawn has been reported. In the present study, released in the Seto Inland Sea,4,5 and Shiranui Sea.6 In growth and reproduction of Chinese white prawn juve- the Ariake Sea, adult Chinese white prawn have been niles released in the Ariake Sea were examined. released for propagation7 and hatchery-reared juveniles have been released since 1986 by the Saga Prefectural Government.8 Chinese white prawn at commercial MATERIALS AND METHODS sizes has been caught in the Ariake Sea after release. However, no juveniles which have been naturally Released juveniles spawned in the Ariake Sea have been found to occur in spite of repeated investigations by net sampling of Larvae that hatched from 15 March to 10 April 1997 juvenile prawns and of small shrimps in commercial were reared at the Sea-Farming Center of Ohura catches.8,9 Fisheries Corporation and Saga Prefecture for nearly 2 months. Adult females that were used for juvenile pro- duction were caught in the Ariake Sea. Juveniles (4.65 million individuals, 22 mm body length on average) were released in the sea near the Michikoshi Fishery Port, *Corresponding author: Tel: 81-9808-8-2571. Fax: 81-9808-8-2573. Ohura, Tara-cho, Saga Prefecture between 30 May and Email: [email protected] 5 June 1997 (Fig. 1). The period 31 March and 1 June Received 7 February 1999. Accepted 5 July 2000. were used as an approximation of the day at hatching 1088 FISHERIES SCIENCE N Nakashima et al. and release, respectively, since both hatching and release prawn was examined in small shrimps caught by stow were conducted over several days. Therefore, the day of nets, bottom drift nets, minnow nets and so on, totaling hatching was 62 days earlier than that of releasing. 40 times off Saga Prefecture in these years.8,9 In addition During 1993 and 1994, 31 samplings were conducted to these investigations, in 1995–1997 investigations to find juvenile Chinese white prawn spawned in the were conducted using the net to sample juvenile prawn wild off Saga Prefecture between April and June, before at 28 sites off Saga Prefecture (Nakashima N & Ito S, the release of the hatchery-reared juveniles, using a net unpubl. data, 1995–1997). In spite of these efforts no to sample juvenile prawn (0.8 m in diameter, 2.5 m long, juveniles of Chinese white prawn were found in the wild mesh size upper part 2 mm and lower part 1 mm).8,9 before the release of the hatchery-reared juveniles. Moreover, the occurrence of juveniles of Chinese white Therefore, in the present study all juveniles caught after releasing were considered to be hatchery-reared juveniles. Growth and reproduction Sampling was conducted once to three times a month for individuals caught using stow nets, bottom drift nets and so on by fishers between July 1997 and April 1998. Each month 5–25 (totally 474) individuals were sampled. Body length and body weight were measured for all individuals. Growth curves (Bertalanffy,11 logistic,12 Gomperz,12 and Pitcher and MacDonald13) were regressed against days after release and compared for the fitting using AIC.14 In the present study, days after release were used instead of weeks in the original equation13 and the Pitcher and MacDonald’s growth equation for males and logistic curve for females were adopted (Table1). In every month between November and April, 4–27 (total 90) females were dissected and the ovary was fixed with Bouin’s solution. Histological sections were made of the fixed ovaries and stained by Mayer’s hematoxylin and eosin. Ovarian developmental stages were divided into five stages: inactive, developing, ripe, spawned and recovery stages, following the criteria of Minagawa et al.15 Water temperature and salinity data of 11 regular Fig. 1 Areas where juveniles of Penaeus chinensis were observation stations near the bottom of the fishery released and recaptured. (᭹) Location where the juveniles were ground by the Saga Prefectural Ariake Fisheries and released; ( ) the fishery grounds for P. chinensis. Development Center were averaged. Table1 Growth curves fitted for the growth of Chinese white prawn in the Ariake Sea Growth curve Sex Parameter AIC L• Cskor at0 or b Bertalanffy Male 164.9 -0.018 0.74 911.9 [k(t-t0)] Lt = L•{1 - e } Female 207.8 -0.015 -5.55 1337.1 Logistic Male 156.5 1.998 0.044 791.1 (a-bt) Lt = L•/[1 + e ] Female 200.3 1.985 0.034 1169.5 Gomperz Male 158.1 1.184 0.034 816.3 (a-bt) Lt = L•e[-e ] Female 201.2 1.242 0.028 1184.7 Pitcher and MacDonald Male 155.0 -2.925 16.15 0.062 10.71 787.9 -k1 Lt = L•(1 - e ), k1 = C sin[2p(t - s)/365] + k(t - t0) Female 200.0 -0.983 -6.17 0.024 -8.90 1171.8 Lt: body length t days after release, t: days after release. Growth and reproduction of P. chinensis FISHERIES SCIENCE 1089 Fig. 2 Water temperature and salinity near the fishery grounds for Penaeus chinensis. RESULTS Water temperature and salinity Water temperature was lowest (10.3°C) in January and highest (29.2°C) in September (Fig. 2). Salinity was low during and after the rainy season, July and August, 25.3–26.9, while it ranged 28.9–30.6 in other months (Fig. 2). Growth Juveniles released in late May and early June at 22 mm body length grew to 100 mm body length in July and Fig. 3 Growth curve fitted to the Pitcher and Macdonald’s 120 mm in August (Fig. 3). In September body size was formula (male) and Logistic model (female) in Penaeus chinen- different between males (145 mm body length) and sis after release in the Ariake Sea. females (167 mm body length). In November (219– 229 days after hatching) body length reached 154 mm (43.1 g in body weight) in males and 198 mm (93.1 g in Reproduction body weight) in females. After November growth of both sexes almost stopped. Maximum body length and body Vitellogenesis started in January and mature individuals weight was 164 mm and 47.2 g in males and 223 mm and appeared at the end of February (Fig. 4). The percentage 130.6 g in females. of mature individuals reached a maximum in March Male growth was best shown by the Pitcher and (32%), and that at the spawned stage was at maximum MacDonald’s growth formula (and female growth by in April (47%). Vitellogenic oocytes were often observed logistic curve (Table1). in individuals in the spawned stage in March. Minimum 1090 FISHERIES SCIENCE N Nakashima et al. In the Sea of Pohai ovary weight of Chinese white prawn increases remarkably after March and spawning starts in May.3 Based on the data of the present study, in the Ariake Sea Chinese white prawn are considered to have started spawning in late February and peaked between late March to early April. Spawning starts more than 2 months earlier in the Ariake Sea than in the Sea of Pohai. In the Sea of Pohai, Chinese white prawn starts to spawn when the water temperature rises to 13°C.3 In the Ariake Sea water temperature reached 12°C in late February when spawning started. The warmer water temperature in the Ariake Sea is one of the causes of the early start of spawning.