Influence of pre-slaughtering feed restriction on muscle characteristics of farmed sea bass (Dicentrarchus labrax L.) during cold storage.

BACKGROUND: This paper deals with the consequences of dietary restriction or complete starvation before slaughtering on the biochemical and textural characteristics of sea bass muscle. RESULTS: Results showed that only severe feed restriction influenced negatively total body and individual organ weights, and these animals showed lower condition factor as well. Neither moderate feed restriction (up to 50% of the standard ration) kept for 30 days nor total starvation up to 12 days caused significant effects on fish weight and fillet yield. Muscle lipid content was lower in feed-restricted fish, although this parameter was not altered by starvation time. Differences between the two feeding strategies studied were observed in muscle textural and biochemical parameters, and the results point to an influence of the nutritional status on the post-mortem evolution of collagen and myofibrillar proteins, although firmness was not modified. CONCLUSIONS: Moderate feed restriction prior to slaughtering could be advisable in sea bass culture, given that no detrimental effects on fish quality or fish performance were noticed, whereas substantial amounts of feed can be saved.

The metabolic effects of prolonged starvation and refeeding in sturgeon and rainbow trout.

The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.

Effect of starvation and refeeding on digestive enzyme activities in sturgeon (Acipenser naccarii) and trout (Oncorhynchus mykiss).

The digestive enzyme activities were determined in Adriatic sturgeon and rainbow trout during starvation and refeeding period. Overall, the digestive enzyme activities are affected in the same sense in both species. The protease and lipase activities were decreased later than amylase activity. Even after 1 month of starvation, both species would be prepared to digest protein and lipids in an effective way. After 72 days of starvation, the digestive machinery of the sturgeon and of the trout shows an altered capacity to digest macronutrients. The capacity to digest proteins and lipids, after 60 days of refeeding, begins to become re-established in sturgeon and trout. In contrast, in this period, the capacity to digest carbohydrates remains depressed in both species.

Adaptive branchial mechanisms in the sturgeon Acipenser naccarii during acclimation to saltwater.

Variations of Na(+)/K(+)-ATPase activity and fatty-acid composition in the gills of the sturgeon Acipenser naccarii subjected to progressive acclimation to full seawater (35 ppt) were determined in relation to the hypo-osmoregulatory capacity of this species in the hyperosmotic medium. Blood samples were taken and gills arches were removed at intermediate salinity levels between 0 and 35 ppt and after 20 days at constant salinity (35 ppt). Plasma osmolality and Na(+)/K(+)-ATPase activity increased significantly with growing environmental salinity. Total saturated fatty acids (SFAs) decreased, while total polyunsaturated fatty acids (PUFAs) increased significantly with increasing salinity due mainly to changes in n-3 PUFAs (20:5n-3 and 22:6n-3). The n-3/n-6 ratio increased significantly during the acclimation process. The results show a direct relationship between salinity, increased gill Na(+)/K(+)-ATPase activity and ultrastructural changes of the gill chloride cells. Changes in the fatty-acid composition in gills of A. naccarii during progressive acclimation to full seawater suggest that variations of gill fatty acids may also have a role in osmoregulatory mechanisms.