M. D. Ayala

Early temperature effects on muscle growth dynamics and histochemical profile of muscle fibres of sea bass Dicentrarchus labrax L., during larval and juvenile stages

Recently, it has been found that the thermal experience during the earliest phases of development could determine the larval and postlarval growth characteristics of teleosts. In order to investigate the effects of the early temperature regime on the advanced stages of growth of sea bass, Dicentrarchus labrax L., this species was reared during the vitelline phase at two temperatures: natural temperature (i15 jC) and 17.7F0.1 jC, and then larvae transferred to common temperature (natural temperature). Muscle growth was studied by morphometric and histochemical techniques (mATPase and NADH-TR). Body length and body mass were also measured. During the vitelline phase, muscle growth was similar in both experimental groups, but at 25 days, both hypertrophy and hyperplasia of white muscle fibres were greater in the prewarmed group (p<0.05). At the end of metamorphosis (80 days) and at 120 days, the average diameter of white muscle fibres, as well as the body length, were greater in the prewarmed group (p<0.05), but the number of white fibres did not differ significantly between groups. The morphological mosaic of white muscle fibres was observed at the end of metamorphosis, and the histochemical mosaic appeared gradually since the early postlarval stages. Thus, at 120 days, some specimens in both experimental groups showed three or four different mATPase staining white fibres: low (L), moderate (M), high (H) and/or very high (vH), whereas in other specimens, only L or M mATPase activity fibres were observed. Early T influenced the histochemical maturity of the

Temperature effect on muscle growth of the axial musculature of the sea bass (Dicentrarchus labrax L.)

In order to determine the temperature effect on the axial muscle growth of sea bass, a stock of larvae was subjected to the following incubation and cultivation temperatures, respectively: 15°C/ambient, 15/17°C, 17°C/ambient and 17/17°C. In all groups the cross‐sectional area of white and red muscles and the number and average area of the white and red muscle fibres were quantified. Results showed that the embryonic period, pre‐larval phase and the end of metamorphosis were accelerated at higher temperatures. During the endogenous feeding period, muscle growth took place by fibrillar hypertrophy, and was not influenced by the temperature. Thereafter (external feeding) muscular hyperplasia began, and growth of all the muscular parameters was favoured by the effect of high incubation and cultivation temperatures, with the latter having higher influence. High incubation temperature had an slight effect on muscle growth and body length, which was only observed from 15 days. Metamorphosis finished at 3 ± 0.4 cm in all the larvae, but this length was earlier reached at higher temperatures. At 120 days, the largest growth was obtained in the larvae maintained at a higher temperature.

Red muscle development of gilthead sea bream Sparus aurata (L.): structural and ultrastructural morphometry.

The transverse red and white muscle area, the superficial red muscle fibres area and their percentages of mitochondria (%mit), myofibrils (%myof) and sarcoplasm (%sarc) were determined in the Mediterranean teleost gilthead sea bream, Sparus aurata (L.). Fish aged from hatching to 78 days were studied. The proportional growth of the red and white muscles was higher for the red muscle in the first half of the larval stage (1–35 days). Then the opposite relationship was observed. The hypertrophic growth of the superficial muscle fibres was continuous except in the first week after hatching. The percentage of mitochondria and percentage of myofibrils showed a significant change just after the half of the larval stage. Whereas the %mit of the superficial muscle fibres was higher than %myof from the first week after hatching to 35 days (average 66.64 %), then the %mit decreased significantly and at 73–78 days both parameters were close to an average value of 50 %. The meaning of these morphological changes is discussed in relation to the functional role of the red muscle of larvae and the onset of the gills respiration.

Posthatch development of the axial musculature of the common dentex Dentex dentex, L (Teleostei)

The common dentex is a promising candidate for Mediterranean aquaculture. The present work is aimed at describing the development of the axial musculature from hatching to postlarval life. Transmission electron microscopy, histochemical (NADH-TR and mATPase) and immunohistochemical techniques (S-58 and TUNEL) have been used. At hatching superficial red and deep white muscles can be distinguished. Presumptive dermomyotome (external) cells are initially located over the superficial red muscle but shortly (2 days) tend to concentrate towards the epaxial and hipaxial limits of the myotome. Then, these cells enter the myotome and spread around and within the white muscle thus being apparently responsible for the stratified hyperplasia of the myotome. Mosaic hyperplasia is activated during the second half of the larval period and initially relies on differentiation of a population of atypical premyoblastic cells (APC). APC are mononuclear cells with euchromatic nuclei, cytoplasms full of thin longitudinally projected tubules, occasional mitochondria and scattered ribosomes. By the end of the larval period these cells tend to disappear, partly due to apoptosis, but postlarval mosaic hyperplasia continues by differentiation of presumptive myosatellite cells. APC are an unexpected and singular finding of this study which deserves more research, so as to further characterize their ancestry, developmental programme and fate. In addition to the white and superficial red muscle fibres, intermediate (pink) and tonic fibres appear during larval metamorphosis. Later, during the early postlarval life, a new type of slow twitch red muscle fibre is differentiated (red adult type).

Effect of thermal treatment on muscle tissue structure and ultrastructure of wild and farmed sea bass, Dicentrarchus labrax L

The present work studies the muscle tissue structure and ultrastructure in two populations: wild and farmed sea bass, Dicentrarchus labrax L., in both raw and cooked states. Results found in fresh raw muscle tissue ultrastructure of wild sea bass showed some typical early post-mortem alterations: fibre-to-fibre detachment, detachment of myofibrils to endomysium and swelling of mitochondria and sarcoplasmic reticulum, mainly. In cooked samples of wild and farmed groups, sarcolemma and endomysium were disrupted and coagulated in most of the zones. Myofibrils were detached from sarcolemma–endomysium. Electron-dense aggregates were observed in both subsarcolemmal and interstitial spaces. These granular aggregates also appeared close to sarcolemma and endomysium, like an electron-dense chain. The interstitial material was quantified in both groups, and it was more abundant in farmed than in wild specimens. The size of the cooked fibres was better preserved in wild than in farmed sea bass, which evidences a higher thermal resistance of muscle tissue in wild specimens.