The fish farming industry has an interest in the rearing of triploids as a means to prevent 26 sexual maturation in fish before they reach their optimal commercial size (Felip et al., 27 1999). Additionally, the production of triploid fish ensures that any that escapees from 28 aquacultural facilities are not able to reproduce in the wild. However, the production of 29 triploid fish has often been associated with an increased incidence of morphological 30 malformations, including abnormal jaws and fins (Sutterlin et al., 1987; Jungalwalla, 31 1991; McGeachy et al., 1996;Sadler et al., 2000;Oppedal et al., 2003), abnormal tail 32 and trunk proportions (Swarup, 1959), facial deformities (Tave et al., 1993) female by application of a cold-shock shortly after fertilization, as described by Piferrer 49 et al. (2000Piferrer 49 et al. ( , 2003. 50 3 The triploidy ratio within each progeny group was estimated by flow cytometric 51 analysis of embryos from 120 eggs sampled 48 hours post-fertilization using an FC500 52 flow cytometer (Beckman Coulter, Ca, U.S.A.), and following a modified version of the 53 method described by Lecommandeur et al. (1994). The triploidy ratios achieved in each 54 progeny were 87, 94, 95 and 97%). Only the progeny from the mating producing the 55 highest triploid rate (97%) were examined further. Thereafter, treated (3n) and control 56 (2n) larvae were reared separately in four 1000-l tanks. When they were 2 months old, 57 fish were vaccinated against Vibrio sp. by immersion in Gava-3 (100mL/L) 58 (Laboratorios HIPRA, Girona, Spain). Periodic OX-CTA (OX Laboratories, Barcelona, 59Spain) baths (50mg/L) were administered throughout the experiment to prevent the 60 presence of parasites. At 5 months of age, random samples of diploid and triploid fish 61were placed into four 3800-l tanks (2 tanks per ploidy group and 50 fish per tank). The 62 tanks were provided with flow-through water (40 l/min), and the fish were reared under 63 natural photoperiod and temperature conditions. The fish were fed by automatic feeders 64 providing dry pellets of increasing size (Skretting, Burgos, Spain) 7 days a week until 65 they reached 12 months of age. 66At both 6 and 12 months, 10 fish were sampled from each tank. The fish were 67 euthanized with an overdose of the anaesthetic MS-222 (500 mg/l, Sigma-Aldrich, 68Madrid, Spain). The ploidy level of each fish was determined by measurement of the 69 individual mean length of the erythrocyte major axis (30 erythrocytes per fish) in a 70 blood sample, stained with Hemacolor (E. Merck. Darmastadt., Germany), as 71 previously described by Piferrer et al. (2003). The individual mean length was then 72 compared with the overall mean length for diploids and triploids. The mean erythrocyte 73 major axis length was 11.5 ± 0.51 µm (mean±SD) in control diploids and 15.3 ± 0.29 74 4 µm in cold-shock treated triploid fish (P<0.001). All fish were confirmed to be of the 75 ploidy level appropriate to their corresponding test group. 76Fish were photographed with ...