A. García-Alcázar

Digestive enzymatic profile of Dentex dentex and response to different dietary formulations

Digestive physiology of on-growing common dentex (Dentex dentex), including protease, amylase and lipase activity in stomach, pyloric caeca, anterior and posterior intestine, was evaluated. The influence of dietary macronutrient balance on these digestive processes was also assessed. Four experimental diets with different protein:lipid:carbohydrate ratios (43/16/28; 43/24/4; 38/19/28 and 38/24/13) were formulated. The highest activity for acid proteases was located in the stomach at pH 1.5. Alkaline proteolytic activities showed the highest values in the pyloric caeca and posterior intestine at pH 8.5-9.0. Dentex showed substantial amylase activity in the pyloric caeca and posterior intestine. Lipase activity was higher in the pyloric caeca, anterior and posterior intestine and was not detected in the stomach. Feed composition influenced alkaline protease activity in the anterior and posterior intestine and was higher for the diet with less protein and more carbohydrates. Enhanced amylase activity was observed in the pyloric caeca and posterior intestine in those groups fed on higher carbohydrate and lower lipid level diets. High dietary carbohydrate levels produced the highest lipase activity but this only occurred in the anterior intestine. We can conclude that the digestive tract of dentex adapts well to protein digestion and possesses a high potential for digesting the other dietary macronutrients, too. Dietary carbohydrate content seems to induce changes in protease, amylase and lipase activity.

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 °C/natural, 17 °C/natural, 15/19 °C, 17/19 °C (natural T averaging 15 °C 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 °C) 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 °C 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 stages (20–55 days), both parameters were greater at 19 °C (P<0.05). Metamorphosis finished earlier at 19 °C. At this stage, Atl. larvae reared at 19 °C showed higher value of total myotomal area than at natural T, while in Med. sea bass, larvae reared at 19 °C showed a lower size of the myotome than at 17 °C/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 °C/natural than at 15 °C/natural. Following metamorphosis, all groups showed a rapid growth, but higher at 19 °C (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.

Muscle Cellularity at Cranial and Caudal Levels of the Trunk Musculature of Commercial Size Sea Bass, Dicentrarchus labrax (Linnaeus, 1758)

In eight specimens of Atlantic sea bass of commercial size (≅350 g) muscle cellularity was studied at two selected sampling levels of the trunk axial musculature: caudal (anal opening) and cranial (fourth radius of the dorsal fin). The following parameters were quantified at both sampling levels: white muscle cross‐sectional area, white muscle fibre diameter (900–1200 fibres), muscle fibre number and muscle fibre density. Results showed a higher total cross‐sectional area at cranial than at caudal level (P < 0.05), what is related with their different gross morphology. However, the white muscle fibre size distribution, as well as the muscle fibre number and density did not show significant differences between them. This study contributes to typify muscle fibre sampling in sea bass of commercial size what is of great interest for morphometric studies where white muscle cellularity is commonly correlated with textural or organoleptic parameters.

Early muscle injuries in a standard reared stock of sea bass Dicentrarchus labrax, (L.)

Abstract An early myopathy affecting the myotomes of a stock of sea bass is described. By electron microscopical examination different degrees of muscle lesions were first detected in recently hatched larvae. Muscle fibres underwent a degenerative process, that according to the gravity of the lesions and age of the fish was sequenced in four stages. Necrotic muscle fibres were abundant in the myotomes of post-larvae (more than 60 days). Although this degenerative myopathy is non-specific, the importance lies in its progressive sequence. Vitamin E-selenium deficiency and uncontrolled peroxidation of the lipid content in the feed is thought to be the cause of the problem. The possible implication of the myopathy in the appearance of a high percentage of lordosis in the same stock of sea bass is discussed.