Temperature effects on muscle growth in two populations (Atlantic and Mediterranean) of sea bass, Dicentrarchus labrax L.

Two genetically different populations of sea bass, Dicentrarchus labrax L., Atlantic (Atl.) and Mediterranean (Med.), were subjected to the following incubation/cultivation temperatures (T): 15 degreesC/natural, 17 degreesC/n atural, 15/19 degreesC, 17/19 degreesC (natural T averaging 15 degreesC and raising gradually). Muscle cellularity was measured at different larval st ages for each T regime. During the vitelline phase, muscle growth was mainl y due to muscle fibre hypertrophy. In Med. larvae, higher incubation T (17 degreesC) increased the area of white and red fibres at hatching, while in Atl. larvae there was no significant T effect at this stage. At mouth openi ng, the area of white fibres increased at 19 degreesC in Atl. larvae (P < 0 .05), but in Med. larvae it was similar for all temperatures. Following yol k-sac reabsorption, hypertrophy and hyperplasia increased in both populatio ns. In these sta-es (20-55 days), both parameters were greater at 19 <degre es>C (P < 0.05). Metamorphosis finished earlier at 19 <degrees>C. At this s tage, Atl. larvae reared at 19 degreesC showed higher value of total myotom al area than at natural T, while in Med. sea bass, larvae reared at 19 degr eesC showed a lower size of the myotome than at 17 degreesC/natural. In lar vae from both populations reared at natural T, incubating T had a positive effect at the end of metamorphosis, thus the total myotomal area were highe r at 17 degreesC/natural than at 15 degreesC/natural. Following metamorphos is, all groups showed a rapid growth, but higher at 19 degreesC (P < 0.05). The results indicate that muscle cellularity was clearly influenced by T, and that both populations had different levels of response. These differenc es can be apparently associated with their respective genetic background. ( C) 2001 Elsevier Science B.V. All rights reserved.