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/natural, 15/19 degreesC, 17/19 degreesC (natural T averaging 15 degreesC and raising gradually). Muscle cellularity was measured at different larval stages for each T regime. During the vitelline phase, muscle growth was mainly 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 opening, 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 yolk-sac reabsorption, hypertrophy and hyperplasia increased in both populations. In these sta-es (20-55 days), both parameters were greater at 19 <degrees>C (P < 0.05). Metamorphosis finished earlier at 19 <degrees>C. At this stage, Atl. larvae reared at 19 degreesC showed higher value of total myotomal area than at natural T, while in Med. sea bass, larvae reared at 19 degreesC showed a lower size of the myotome than at 17 degreesC/natural. In larvae from both populations reared at natural T, incubating T had a positive effect at the end of metamorphosis, thus the total myotomal area were higher at 17 degreesC/natural than at 15 degreesC/natural. Following metamorphosis, 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 differences can be apparently associated with their respective genetic background. (C) 2001 Elsevier Science B.V. All rights reserved.