Abstract
During their 3–4 first years of life, triploid sea bass Dicentrarchus labrax grew in a similar fashion to diploids in fork length but more slowly than diploids ( P 1 kg) sea bass. The condition factor was reduced in both ploidies during the spawning season which took place in winter when the temperature was low. These observations suggest that any growth advantage in triploids, which were functionally sterile, may be offset by unfavourable environmental conditions. Thus, the potential gain of triploid fish, because they do not direct energy to gonadal growth, could not overcome the effects of low temperature on somatic growth, which coincided with the spawning season. This suggests that the low growth of this species during winter is more a consequence of low temperature than of the energetic cost associated with reproduction. On the other hand, the lower hepatosomatic index in triploid females in contrast to diploid females might be indicative of the lack of gonadal oestradiol‐mediated hepatic synthesis of vitellogenin. Also, erythrocyte and haematocrit measurements showed an increased nuclear and cellular volume in triploids, but with similar cell numbers to those of diploids, respectively.