Larval culture of the king crabs Paralithodes camtschaticus and P. brevipes

Larval culture of the king crabs Paralithodes camtschaticus and P. brevipes

J. Kittaka, B.G. Stevens, S. Teshima, and M. Ishikawa

Larval culture of the king crabs Paralithodes camtschaticus and P. brevipesThis is part of Crabs in Cold Water Regions: Biology, Management, and Economics
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Description

Paralithodes camtschaticus and P. brevipes hatch out as zoeae, metamor-phose into glaucothoe, and molt into juveniles. Zoeae were cultured and fed with Artemia nauplii and diatoms of the genus Thalassiosira (dominantspecies: T. nordenskioldii) in combination, while glaucothoe were nonfeeding. Artemia and Thalassiosira had sufficient content of eicosapentaenoic acid (EPA) but low content of docosahexaenoic acid (DHA). Freeze-dried Thalassiosira were enriched with tuna oil which contained DHA at 23.3%. Hatched Artemia nauplii were fed with enriched Thalassiosira for about 16 hours beginning 8 hours after hatching. The enriched Artemia were fed to zoeae of P. brevipes. The survival rate was 75.9% (A), which was much better than 43.1% (B) fed control Artemia without enrichment. The food value of Artemia fed with enriched Spirulina (C) and enriched beer yeast (D) was also examined. The survival rate was 59.3 and 55.6% for C and D, respectively. Although enriched Artemia feeding improved the survival rate of zoeal stages, survival rate during the glaucothoe stage was poor at 16.2, 8.4, 6.1, and 5.0% for A, B, C, and D, respectively. Heavy mortality of the glaucothoe was apparently due to the white-turbid midgut gland disease. The disease may be controlled by antibiotic treatment; however,water quality control is more important for improving survival rate associated with nutritional enrichment of food.

Red king crab, Paralithodes camtschaticus, and Hanasaki king crab, P.brevipes, are important marine resources in the North Pacific Ocean. Paralithodes camtschaticus is distributed widely in the Okhotsk Sea and Bering Sea while P. brevipes inhabits waters around the Nemuro Peninsula, the Northern Four Islands, and some limited areas around Sakhalin (Sato 1958). The resources have been extensively fished; however, the results of an annual trawl survey (e.g., Stevens et al. 2001) indicate the population of P. camtschaticus in the eastern Bering Sea has been well managed. Another approach to resource management may be stock enhancement by restocking juvenile king crabs. About 200,000 first instar juveniles of P. brevipes have been released annually in Nemuro waters. A serious problem with this technique is heavy mortality after release. King crabs hatch out as zoea larvae. After three molts in P. brevipes and four in P. camtschaticus, they metamorphose into the glaucothoe, and then molt into the first instar juvenile (Kurata 1956, Sato 1958, Kurata 1959). Valuable information has been published on larval feeding of P. camtschaticus (Kurata 1959, 1960; Paul and Paul 1980; Nakanishi and Naryu 1981; Nakanishi 1987, 1988; Paul et al. 1989). They undergo a drastic developmental change during metamorphosis: the mouthparts, appendages, and foregut atrophy and the glaucothoe do not eat (Kittaka, unpubl., presented to the Fifth International Working Group on Crustacean Nutrition Symposium, April 22-24, 1995, Kagoshima, Japan; Abrunhosa and Kittaka 1997a,b). Therefore, the physiological condition of the glaucothoe and early juveniles is primarily affected by nutrition during the zoeal stages.

We carried out larval and postlarval culture experiments in 1996. Food given to zoeae was generally Artemia salina nauplii and cultured diatoms, Thalassiosira nordenskioldii, in combination (Iwamoto et al. 1982; Nagakuraet al. 1983; Kittaka 2000; Abrunhosa 1998). However, culture results fluctuated widely between tanks. Both foods do not necessarily contain the necessary amounts of essential fatty acids for marine decapod crustaceans (Kanazawa 2000). Another cause of fluctuation in survival between years may be disease such as midgut gland necrosis found commonly in cultured crustacean larvae (Liao 1988). Heavy mortality was reported in P.camtschaticus and P. brevipes larval culture due to the midgut gland disease (Watanabe et al. 1998). In order to establish larval and postlarval culture methods for king crabs, we examined the effect of nutritional enrichment of foods to survival rate in 2000.

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