Aquaculture Research, 2002, 33, 1191±1193 SHORT COMMUNICATION Occurrence of hypomelanization in cultured yellowtail flounder Limanda ferruginea C F Purchase*, D L Boyce & J A Brown Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Newfoundland, Canada Correspondence: J A Brown, Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Newfoundland, A1C 5S7, Canada. E-mail: [email protected] *Present address: Department of Zoology, University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario, L5L 1C6, Canada. Flatfish often exhibit abnormal pigmentation under investigated for its potential as a cold-water cultured conditions, e.g. Japanese flounder Para- aquaculture species. Broodstock development along lichthys olivaceus (Temminck & Schlegel) (Seikai, with culture from the egg to the juvenile stage Watanabe & Shimozaki 1987). This is usually ex- have been successful. Current interest on this pressed as a lack of pigment, pseudo-albinism (hypo- species is being devoted to ongrowing of juveniles melanization), on the ocular side or, less often, as (e.g. Purchase, Boyce & Brown 2000). Here, we pigmentation on the blind side (hypermelanization), report the occurrence of hypomelanization in which is normally unpigmented (reviewed by juveniles of this species, which were produced at Venizelos & Benetti 1999). Abnormal pigmentation Memorial University of Newfoundland's Ocean Sci- may be a result of inadequate nutrition, light or ences Centre, near St John's, Newfoundland, Canada. stress during the larval stage (Matsumoto & Seikai Over a period of several years, yellowtail flounder 1992). Whether abnormal pigmentation is the result eggs were obtained from captive broodstock held at of more general metabolic problems is unclear. the Ocean Sciences Centre. Embryo incubation and Matsumoto & Seikai (1992) reported that hypo- larval rearing took place under constant light pro- melanization in Japanese flounder was associated vided by incandescent bulbs. Larvae were first fed with abnormal scale development, where cycloid rotifers (Branchionus plicatilis Muller; enriched with scales were present on the ocular surface in areas culture Selco; INVE, Belgium), and algae (Isochrysis where ctenoid scales normally appear. This con- galbana Parke), followed by Artemia sp. nauplii (en- dition is also present in yellowtail flounder riched with DHA Selco; INVE, Belgium) at about (C F Purchase, pers. obs.). Abnormally pigmented 1 month of age (Rabe & Brown 2000). Juveniles turbot Colistium nudipinnis (Waite) in New Zealand were fed commercial fish pellets (Fry Feed Kyowa) have been shown to have slower growth rates and and kept under 18 h of light per day. are more susceptible to disease than normally pig- Similar proportions of abnormally pigmented fish mented individuals (Diggles 2000). It is possible that occurred over several years at the Ocean Sciences the development of abnormal pigmentation and Centre. In 1998, 327juveniles were examined for scales is linked to a more general metabolic malfunc- pigmentation, eye migration and the orientation of tion in these fish. This was the reasoning behind metamorphosis (i.e. was the ocular side the left or comparing growth rates between normally pig- right side of the body). Fish were examined at mented and hypomelanized fish in our study. 5 months of age and were classified as normally The yellowtail flounder Limanda ferruginea (Storer) pigmented, partially or totally hypomelanized or is a small north Atlantic flatfish currently being hypermelanized. Metamorphosis was recorded as ß 2002 Blackwell Science Ltd 1191 Hypomelanization in cultured yellowtail flounder C F Purchase et al. Aquaculture Research, 2002, 33, 1191±1193 having occurred to the right or left side, and eye migration was scored as complete (normal) or 5 HM incomplete. NP In 1996, a study was conducted to determine the effect of photoperiod on growth and survival of ju- veniles (Purchase et al. 2000). Using their data (Ex- 4 periment 1), we were able to compare growth rates of normally pigmented (NP) and hypomelanized (HM) fish. Briefly, juveniles were placed under 12, 18 and 24 h of light per day, which was pro- 3 vided by 100-W incandescent bulbs. These were placed 60 cm above the water and provided an in- Round weight (grams) tensity of 200 lux. Thirty NP and 10 HM 4.5±5.0 cm 1-year-old juveniles were placed in each 13 L tank. 2 Three replicate tanks were used in each photoperiod treatment. Fish were fed 4% of body weight every 0246810 second day. Seven NP and three HM fish were Week of experiment sampled for length and weight every second week Figure 1 Weight of normally pigmented (NP, squares) for 10 weeks. Growth was compared using analysis and hypomelanized (HM, circles) yellowtail flounder over of covariance with the week of the experiment as the the course of the experiment. Each datum is the mean covariate. Analysis was carried out with a 0.05, pigment specific value for each tank; error bars standard using the minitab statistical package. Further error. details can be found in Purchase et al. (2000). Of the 327juveniles examined in 1998, 56.3% Yellowtail are marketed as both whole fish and a were normally pigmented, 34.2% exhibited some filleted product. There is a general concern that degree of hypomelanization and 9.5% were hyper- abnormal individuals (orientation, eye location and melanized. Yellowtail flounder are right-eyed pigmentation) would be unmarketable as whole flounders, meaning that the right side is normally fish. Although the percentage of cultured yellowtail the ocular side after metamorphosis. The normal flounder currently exhibiting hypomelanization is condition was present in 76.5% of the fish, with high (34.2%), these fish do not seem to have any the remainder having metamorphosed to the oppos- negative traits associated with production, as mor- ite side. Regardless of which side was the ocular, tality and growth rates did not vary from normal 49.5% showed complete eye migration. The correl- fish. Therefore, suggestions of culling such individ- ation coefficients of these characteristics were uals seem to be unwarranted, as long as they are pigmentation±eye migration 0.689, pigmentation± marketable as fillets. orientation 0.208 and eye migration±orientation 0.175. The moderate correlation coefficient for pigmentation and eye migration suggests a possible Acknowledgments relationship between these two traits. We wish to thank the staff of the Ocean Sciences Mortality rates of juvenile yellowtail flounder are Centre for their help in raising yellowtail flounder, generally very low (as was the case during the and the Canadian Centre for Fisheries Innovation experiment) and did not differ among NP or HM and Fisheries Products International for funding fish. The experimental photoperiod treatments had the research. no effect on growth (Purchase et al. 2000), and we therefore combined the samples for the analyses presented here. Average specific growth rates {100 References [(ln final weight±ln initial weight) timeÀ1]} were Diggles B.K. (2000) Chemotherapy of the ciliate Trichodina 1.3% body weight increase per day. There was no sp. on juvenile turbot (Colistium nudipinnis) with notes difference in weight gain (log-transformed data) of on the susceptibility of fish with abnormal pigmentation. NP and HM individuals (ancova: F1, 102 0.07, New Zealand Journal of Marine Freshwater Research 34, P 0.790; Fig. 1). 645±652. 1192 ß 2002 Blackwell Science Ltd, Aquaculture Research, 33, 1191±1193 Aquaculture Research, 2002, 33, 1191±1193 Hypomelanization in cultured yellowtail flounder C F Purchase et al. Matsumoto J. & Seikai T. (1992) Asymmetric pigmentation on occurrence of albinism in hatchery-reared flounder and pigment disorders in Pleuronectiformes (flounders). Paralichthys olivaceus. Nippon Suisan Gakkaishi 53, Pigment and Cell Research Supplement 2, 275±282. 195±200. Purchase C.F., Boyce D.L. & Brown J.A. (2000) Growth and Venizelos A. & Benetti D.D. (1999) Pigment abnormalities survival of juvenile yellowtail flounder Pleuronectes in flatfish. Aquaculture 176, 181±188. ferrugineus (Storer) under different photoperiods. Aqua- culture Research 31, 547±552. Rabe J. & Brown J.A. (2000) A pulse feeding strategy for Keywords: hypomelanization, yellowtail flounder, rearing larval fish: an experiment with yellowtail floun- Limanda ferruginea, Pleuronectes ferrugineus, der. Aquaculture 191, 289±302. pigmentation, growth Seikai T., Watanabe T. & Shimozak M. (1987) Influence of three geographically different strains of Artemia nauplii ß 2002 Blackwell Science Ltd, Aquaculture Research, 33, 1191±1193 1193.