Abderrahmen Bouain

Zooplankton distribution in four ponds of different salinity: a seasonal study in the solar salterns of Sfax (Tunisia)

AbstractThe seasonal distribution of metazooplankton and large-sized ciliates was studied in four ponds of different salinity in the solar salterns of Sfax (Tunisia). Total zooplankton abundance varied from 1 × 103 to 4.7 × 106 ind m−3. Salinity had a negative effect on the abundance of copepods and rotifers which were absent in the pond with the highest salt concentration (180‰) in which the number of taxa was low and Artemia or the ciliate Fabrea largely dominated the zooplankton community. Temperature and the presence of Dunaliella salina as prey appeared as key factors in controlling the abundance of Artemia, while organic detritus appeared as important in the diet of Fabrea. Change in zooplankton species composition along the hypersaline gradient (40–90‰) was primarily related to salinity. However, our data suggest the importance of both the abundance and composition of food in the spatial and temporal variations of some zooplankton species.

Abundance and biomass of prokaryotic and eukaryotic microorganisms coupled with environmental factors in an arid multi-pond solar saltern (Sfax, Tunisia)

The distribution of abundance and biomass of prokaryotes, flagellates, ciliates and phytoplankton, were studied in five ponds of increasing salinity in the Sfax solar saltern (Tunisia) coupled with environmental factors. The results showed that abundance of eukaryotic microorganisms decreased with increasing salinity of the ponds whereas prokaryotes (heterotrophic bacteria and Archaea) were abundant in the hyper-saline ponds. Phototrophic picoplankton was found in a large range of salinity values (70 and 200‰). Phototrophic non-flagellated nanoplankton which dominated in the first sampled pond was substituted by phototrophic flagellated nanoplankton in the other ponds. Heterotrophic nanoplankton dominated in the crystallizer pond but its quantitative importance declined in the less saline ponds. Diatoms and dinoflagellates were the major contributors to phytoplankton abundance in the first ponds (>90% of total abundance). Ciliated protozoa were found in all the ponds except in the crystallizer in which prokaryotes proliferated. Oligotrichida and Heterotrichida were the most abundant ciliate groups. Overall, species richness decreased with salinity gradient. We propose a simplified diagram of the Sfax salterns food web showing the dominant role of the microbial loop along the salinity gradient.

Copepod community structure related to environmental factors from a summer cruise in the Gulf of Gabès (Tunisia, eastern Mediterranean Sea)

We studied the summer spatial distribution of the copepod community in both the neritic and oceanic areas of the Gulf of Gabes (Tunisia, eastern Mediterranean Sea) coupled with environmental factors. Copepods were the most abundant zooplankton throughout the sampling period, contributing 7 8% of the total zooplankton. A total of 14 copepod families were identified in all stations, with an overwhelming abundance of Acartiidae and Oithonidae ( 39 .0 5 and 39 . 09 % of total abundance, respectively). Abundance of Acartia clausi and chlorophyll-a concentrations were negatively correlated with salinity, suggesting that this species probably escaped the high coastal salinity ( 3 8 psu). Significant correlation determined between A. clausi and tintinnids at 5 0 m isobaths indicates that these planktonic ciliates probably served as a substantial food link towards higher trophic levels of this area. Conversely, Oithona nana which was well adapted to high chlorophyll-a concentrations and high salinity along the coast, showed significant correlations with Dictyochophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae, suggesting that this small copepod was capable of feeding on a wide selection of phytoplankton preys.

Rearing of Fabrea salina Henneguy (Ciliophora, Heterotrichida) with three unicellular feeds

The growth rate of the ciliate Fabrea salina was studied in batch cultures in the presence of three feeds, tested separately from each other: the Prymnesiophyceae, Isochrysis galbana obtained from pure culture, the Chlorophyceae Dunaliella salina, and the commercially available yeast Saccharomyces cerevisiae. F. salina, and D. salina were harvested below the surface from the first evaporation pond and the crystallizer pond, respectively in multi-pond salterns (Sfax, Tunisia). The highest density of Fabrea was recorded with I. galbana (26 ind ml(-1)). However, the greatest length (243 microm) was recorded with Fabrea fed with D. salina. The lowest density, length and biovolume values were recorded with Fabrea fed with S. cerevisiae. The ANOVA test showed that density (F=18, d.f.=57), length (F=33, d.f.=57), and biovolume (F=19, d.f.=57) of Fabrea fed with yeast were significantly different (p<0.001) from those when Fabrea was fed with D. salina and I. galbana. The ciliate Fabrea encountered in the Sfax saltern (Tunisia) might be a valuable food source for Tunisian marine fish hatcheries.

Age, growth and reproduction of Raja miraletus (Linnaeus, 1758) (Chondrichthyes: Rajidae) of the Gulf of Gabès (Tunisia, Central Mediterranean Sea)

Abstract Age and growth of the brown ray, Raja miraletus, was estimated from ring counts on vertebral sections from 95 females (13.5–56.0 cm total length (TL)) and 85 males (13.5–58.0 cm TL) collected from the Gulf of Gabès (Central Mediterranean, Tunisia) during 2007. Marginal increment and edge analyses suggest annual band pair formation. The oldest female and male brown rays were 9 and 7 years old, respectively. Von Bertalanffy growth parameters are L8 = 69.20 cm TL, k=0.18 year–1 and t 0=–0.11 years for females, and L8 = 67 cm TL, k=0.22 year–1 and t 0=–1.01 years for males. Longevity estimates were 19.25 and 15.75 years for females and males, respectively. Based on life history parameters, natural mortality estimation M was in the range 0.37–0.47 for females and 0.60–0.61 for males. Males were found to mature between 28 and 43 cm TL and L50% was estimated at 34.31 cm TL (21.91 cm DW). Females mature between 33 and 48 cm TL and reached L50% at 41.8 cm (27.10 cm DW). Age at sexual maturity (A50%) was estimated at 2.7 years for males and 4.41 years for females. Females and males have an annual reproductive cycle. Mating occurred mostly through spring and summer.

Food and feeding habits of Caranx crysos from the Gulf of Gabès (Tunisia)

The diet of blue runner Caranx crysos (Carangidae) in the Gulf of Gabes (Tunisia, Mediterranean) is described from analysis of stomach contents (N = 1668 fish). The majority of samples were obtained from commercial purse seine and gill-net catches. The index of vacuity (%VI) was relatively high (58.7%) and differed significantly across months. Blue runner is an opportunistic predator that consumes mostly pelagic organisms, with benthic prey representing only a small proportion of the diet. The diet was quantified using the frequency of occurrence (%F), numerical abundance (%N), weight (%W) and the index of relative importance (IRI and %IRI) for each prey taxa. The most important prey categories were teleosts (%IRI = 83.4) and crustaceans (%IRI = 16.6), with molluscs only observed occasionally (%IRI < 0.1). Fish were also the dominant food items in both terms of weight (89.60%) and frequency of occurrence (82.44%). In terms of numerical abundance, crustaceans were the most abundant prey (78.07%). Ontogenetic and seasonal differences in the diet were observed, although there was no difference between the diets of males and females.

Age, growth, sexual maturity and reproduction of the thornback ray, Raja clavata (L.), of the Gulf of Gabès (south-central Mediterranean Sea)

Abstract The thornback ray Raja clavata is one of the most abundant bycatch species of trawl fishing in the waters of the Gulf of Gabès, but little is known about its life history in this area. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. The age of individuals was estimated by counting growth bands on central vertebral sections. Marginal increment and edge analysis supported the hypothesis of annual deposition of growth bands, with the opaque band formed during autumn. The parameters estimated from von Bertalanffy and Gompertz growth functions showed differences between sexes. The oldest thornback ray female was aged 15 years (104 cm TL), whereas the oldest male was 12 years (89 cm TL). Variations in the gonadosomatic and hepatosomatic indices of both sexes and the presence of vitellogenic activity in mature females during the year indicated that the species cannot be considered to be a continuous spawner. Males were found to mature between 55 and 75 cm TL, whereas females matured between 72.4 and 85 cm TL. The TL at which 50% of the population reached maturity was 67.44 and 81.42 cm for males and females, respectively. Males and female thornback rays mature, respectively, at approximately 5.3 and 7 years old.

Comparison of the effects of four cooking methods on fatty acid profiles and nutritional composition of red mullet (Mullus barbatus) muscle

This study was performed to examine the effects of different cooking methods (frying, steaming, oven cooking, and microwave cooking) on proximate chemical composition, mineral contents, and fatty acids profiles of red mullet (Mullus barbatus) fillets. The frying process caused a significant increase in fat content (from 13.37±0.04 to 34.44±0.20 g/100 g d.w.) and reduced the proportion of the palmitic acid of 50.73% and saturated fatty acids of 56.9%. While, the proportion of polyunsaturated fatty acids (PUFA) increased from 4.04% of total fatty acids for raw fillet to 49.17% of total fatty acids for fried fillets. The steamed, oven-cooked, and microwave-cooked fillets showed the best proportion of fat content, PUFA, and ω-6/ω-3 ratio as compared with fried red mullet fillets. Na, Mg, and Zn contents of cooked fish fillets significantly decreased.

Biology of little tunny Euthynnus alletteratus in the Gulf of Gabes, Southern Tunisia (Central Mediterranean Sea)

Se describen algunos parametros biologicos de la bacoreta Euthynnus alletteratus en el Golfo de Gabes (sur de Tunez), tales como la proporcion de sexos, el Indice Gonado-Somatico (IGS), el Indice Hepato-Somatico (IHS), la longitud de primera madurez sexual, y la relacion longitud-peso. Se analizo un total de 397 specimenes (244 hembras y 153 machos) entre los 36,7 y 97,8 cm de longitud, con un promedio 52,29 ± 5,87 cm. Las muestras se recolectaron mensualmente, entre enero de 2008 y diciembre de 2009. El 61% de los ejemplares fueron hembras. El periodo de desove se extiende de junio a septiembre, calculado a partir de los altos valores de IGS. Las relaciones longitud-peso revelaron que la bacoreta presenta una alometria negativa. La longitud promedio de primera madurez de las muestras tomadas en el Golfo de Gabes fue de 44,8 cm de longitud de horquilla para las hembras y 42,8 cm para los machos.

Status of cetaceans in Tunisia through analysis of stranding data from 1937 to 2009

Abstract A survey of cetaceans stranded along the Tunisian coastline (2004–2009) and a review of the literature allowed us to record a total number of 132 stranding events from 1937 to 2009. They included two species of balaenopteridae, one species of physeteridae and five species of delphinidae. The common bottlenose dolphin Tursiops truncatus (Montagu, 1821) and the fin whale Balaenoptera physalus (Linnaeus, 1758) were the main stranded species in 83 and 21 stranding cases, respectively, representing 78.78% of all records. Stranding events occurred all the year round, with the highest frequency in spring (21.68%) and summer (50.60%) for the common bottlenose dolphin and in winter for the fin whale (50%). The common bottlenose dolphin was more vulnerable to human and fisheries interaction while the fin whale was more prone to be trapped in shallow waters.