Delayed growth of albino in Japanese flounder larvae and juveniles

Albino is one of the genetic diseases which cannot produce melanin according to the mutation of tyrosinase and tyrosinase-related genes. In the Japanese flounder Paralichthys olivaceus, body color anomaly as pseudo-albinism, which can produce melanin unlike albino, has been frequently reported under hatchery conditions. The appearance of the albino with red eyes and brighter body colors than wild-type pigmentation (including hetero and normal genotypes), in hatchery-reared Japanese flounder juveniles, was firstly reported by Shikano. However, basic information of surviving abilities in albino larvae and juveniles has not been reported. Albinos were found in a hatchery population at Fukushima Prefectural Sea-Farming Institute (Okuma, Fukushima). This population was produced by parental fish originated from aquaculture farms at Kagawa and Kochi Prefectures, and domesticated for at least two or three generations at Hakatajima Station (Imabari, Ehime), National Center for Stock Enhancement, Fisheries Research Agency, Japan. A part of the above-mentioned albinos were transported and reared as parental fish in the Research Center of Marine Bioresources, Fukui Prefectural University (Obama, Fukui) since November 2002, and their males and females matured in 2003 and 2004, respectively. Wild females, captured from the western part ofWakasa Bay (Maizuru, Kyoto) in 2003, were reared as brood fish with completely normal genotype. The hetero group (03H group) was created by the crossing of artificial fertilization between the albino male and the wild female. The present study performed the crossing experiments by artificial fertilization in 2005 and 2006 as follows: albino/albino (9 females/9 males, A group; 9 families); albino/ normal or normal/albino (3 females/3 males or 2 females/2 males, H group; 5 families); and normal/ normal (4 females/4 males, N group; 4 families). Each family was reared separately under common environmental conditions. In addition, the authors compared the growth and surviving ability between albino and hetero types in the same rearing tanks, according to the crossing between albino female and 03H group hetero male (AH group; 3 families). Larvae and juveniles were reared at 20 1°C, in 100 L tanks in a water bath (1.5 ¥ 4.0 m), until 40 days after hatching (DAH), and their foods were provided as the previous report. Larvae and juveniles in all groups were reared under less than 0.1 lux using shading curtain. The stocking number of larvae in A, H and N groups started from 2000 individuals/tank on 0 DAH, and was adjusted to 1000 and 500 individuals/tank on 10 and 20 DAH, respectively. Twenty to 50 individuals from all families in A, H and N groups were randomly sampled on 0, 3, 5 and 10–40 (every 5 days) DAH. The stocking number of larvae in the AH group started from 1000 individuals/30 L tank on 0 DAH, and larvae were sampled more than 100 individuals/tank on 0, 1, 3, 5, 10 and 20 DAH from each tank. All samples were fixed by phosphate buffered 4% *Corresponding author: Tel: 81-770-52-6300. Fax: 81-770-52-6003. Email: seikai@fpu.ac. jp Present address: Ecological Genetics Research Unit, Department of Biological and Environmental Sciences, Biocenter 3, Viikinkaari 1 FIN-00014, University of Helsinki, Finland. Received 4 October 2006. Accepted 1 December 2006. FISHERIES SCIENCE 2008; 74: 455–457