The influence of season on the gonad index and biochemical composition of the sea urchin Paracentrotus lividus from the Golf of Tunis.

Seasonal variation in the gonad weight and biochemical composition of the sea urchin Paracentrotus lividus from the Golf of Tunis (Tunisia) were studied between September 2003 and August 2004. The highest gonad indices occurred in March (16.71%). The spawning period occurred between April and July and resulted in a fall in gonad indices to low level (7.12 ± 0.12%). Protein constituted the main component of the gonad, and lipid and carbohydrate were found at appreciable amounts. Consistent with the gonad cycle, sea urchin biochemical components showed clear seasonal variation with a significant decrease during the spawning period. The polyunsaturated fatty acid (PUFA) group was found at high level (40% of the total fatty acids). Of the PUFA group, eicosapentaenoic (C20:5 n - 3) and eicosatetraenoic (C20:4 n - 3) were the most abundant gonadal lipids. The level of PUFA was significantly affected by temperature variation showing an increase during the cold months and a decrease in the hot months.

Tissue parameters of the sea urchin (Paracentrotus lividus): the effects of magnesium and transport stress.

The present study investigates some biochemical and biological variables in sea urchins (Paracentrotus lividus) that were stressed in the course of collection, transportation and laboratory conditioning and the effect thereon of pre-treatment with a test compound; magnesium chloride (MgC12). Handling and transportation for 5h resulted in significantly decreased gonadal indices due to unplanned spawning. The pre-treatment of sea urchins with 5 mmol 1(-1) MgCl2 reduced unplanned spawning during all of the experiments. Protein content and humidity were significantly higher (p < 0.05) in sea urchins treated with Mg than in the control group, these differences between groups were maintained throughout the experimental period. The analyses of gonad mineral compounds (Na+, K=, P, Ca2+ and Mg2+) showed a significantly higher (p < 0.05) Na+ and K+ tissue contents in the Mg-treated group than the control group throughout the conditioning period. Phosphorus with initial similar levels in both groups, however, showed a significantly higher gonad level (p < 0.05) in the Mg-treated group towards the end of the experiment (> 9 days).

Lipids and fatty acids composition in the tissues and by-products of two Tunisian shrimp species from the north and south regions.

Total lipid and fatty acid composition was determined in the muscle and by-products (heads, shells and tails) of Penaeus kerathurus and Metapenaeus monoceros caught off the North and South coasts of Tunisia. Shrimp total lipid levels in by-products ranged between 2 to 3.15% (p < 0.05) and were higher than fat tissue levels in both groups. No significant difference was found between tissue and by-product lipid contents of M.monoceros from both regions. However, significantly higher lipid content was found in P.kerathurus from the South than the North area. The percentage of polyunsaturated fatty acids were important in the tissues and by-products of both species from both regions. Thus, polyunsaturated fatty acids constitute the major fraction followed by saturated fatty acids and monounsaturated. The main fatty acids in both shrimp species muscle and by-products were C16:0, C20:5n-3, C22:6n-3, C18:1n-9, C18:0, C16:1, C20:4 and C18:1n-7.

Nitrogen effects on proteins, chlorophylls and fatty acids during the growth of Arthrospira platensis.

Spirulina platensis (=Arthrospira platensis) is a tunisian strain which has been isolated for the first time in Oued Essed (Sousse, Sidi Bou Ali). Biomass evolution, proteins, chlorophylls and fatty acids composition of this alga were monitored by varying nitrogen concentrations in the culture medium. Nitrogen stress was provoked by adding sodium nitrate (NaNO3) in the culture medium with concentrations varying from 0 to 5 g/l. Results obtained showed that nitrogen depletion increased total proteins and total chlorophylls. The addition of NaNO3 (5g/l) led to an increase of total fatty acids amounts and modify fatty acids composition. Optimal quantities of palmitic, gamma -linolenic and oleic acids were obtained with NaNO3 free-cultures. Thus, the tunisian strain has valuable biological substances, worthy to determine the optimal conditions for its propagation.

Chlorophylls, proteins and fatty acids amounts of arthrospira platensis growing under saline conditions.

Spirulina platensis (Arthrospira platensis) is a Tunisian strain isolated for the first time, in Tunisia, in Oued Essed (Sidi Bou Ali, in Sousse region). Evolution of biomass, proteins, chlorophylls and fatty acids (FA) has been followed during Spirulina growth. Experiments were carried out by varying sodium chloride concentrations in the culture medium in a range from 1 g L(-1) (natural environment) to 60 g L(-1). Results analysis showed an increase in chlorophyll amounts at 15 g L(-1) NaCl in 10 days old cultures but a decrease at high NaCl concentrations. Optimal proteins amounts was observed at 15 g L(-1) NaCl in young cultures (5 and 10 days). FA composition was modified by NaCl and depended on culture age. Cultures exposed to high salinity concentrations showed not only a decrease in growth rate but also a loss in total fatty acids TFA quantities. Samples cultured over 15 days at 30 g L(-1) NaCl rendered optimal quantities of lipids and gamma-linolenic acid.