Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Organic extracts of the sponge Aplysina fistularis (Pallas 1766) were tested for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus) and Gram negative bacteria (Escherichia coli, Klebsiel­ la pneumoniae and Pseudomonas aeruginosa). The minimal inhibitory concentration (MI C) and toxic activity of extract were determined. Susceptibility trials of organic fractions obtained by V LC: Hexane, EtOAc and CHCl, showed that EtOAc fraction has antibacterial activity against E. coli, while CHCl, fraction inhibited E. coli and S. aureus growth. The later refractioning of EtOAc fraction and the biodirected assays showed that fractions FI2 and F 13 of EtOAclHex and EtOAc F 14 were bioactive against Gram positive and Gram negative bacteria. Only EtOAc/MeOH Sf2 from subfractionig of EtOAc FI4 produced inhibition for E. coli and S. aureus. In Sf2 EtOAc/MeOH , MIC was moderate for S. aureus (MIC > 256 g/ml). F4 CHCI3IMeOH produced a high inhibition in S. aureus (MIC = 0.125 g/ml) and for E. coli (MIC > 16 g/ml). F10 CHCl3/MeOH showed a moderate activi­ty against S. aureus(MIC > 128 g/ml) and low activity against E. coli (MIC = 512 g/ml). F10 CHCl3/MeOH did no present toxic activity against Artemia salina. The fractious F4 CHCl3/MeOH and Sf2 EtOAc/MeOH were toxic for this organism when the concentration was higher than 100 μglml. LC50 in both cases was 548.4 and 243.4 μg/ml respectively. Secondary metabolites of medium polarity obtained from A.fistularis have a wide spec­trum of anti bacterial activity. Toxicity analysis suggests that only F10 CHCl3/MeOH has potential as an antimi­crobial agent for clinical use.

Temperature affects growth rate in aquatic organisms. This can be evaluated in short term using biochemical indexes (RNA/DNA and Protein/DNA). The effect of acclimatization temperature on the instantaneous growth and physiological condition of Perna viridis was studied in organisms collected in La Esmeralda, Sucre Slate (Venezuela) and taken to the laboratory, where groups of 100 organisms (size 3.0 - 3.5 cm, aliteroposlerior measurement) were acclimatized at 15, 20, 26 or 28°C during four weeks. Later they were kept in a 60 liters aquarium for another six weeks under the same conditions. Each week, ten organisms per group were extracted to measure concentrations of RNA, DNA (by a fluorometric method with ethidium bromide) and proteins (by a colorimetric method), in tissues (digestive gland, adductor muscle and gills). Protein concentration was greater and highly significant at 15°C for all studied tissues. The opposite was obtained with the RNA/DNA and Protein/DNA ratios: the greatest increase was observed at the highest temperature (28"C) for all tissues. At the low­ est temperature there was a tendency 10 reduce both indexes with time. Greater instantaneous growth can be expected at higher temperatures and 28"C was optimal for growth in these specimens.

We examined the spat availability the oyster Pteria colymbus at 6-8 and 19-21 m depths for 15 months (March 1993-June 1994) in Turpialito, Golfo de Cariaco, Venezuela. Spats were trapped using artificial collectors (plastic fílaments in bags, 30 x 60 mm), suspended from a long line. Each collector was replaced by a replica monthly to analyse abundance, shell dimension and mass of P colymbus. Intraweekly, the temperature, salinity, oxygen and food availability (Chlorophylla, total seston, organic and inorganic seston) were determinated. There is juvenile recruitment all year, suggesting continuous reproduction. Spat counts were higher at 6-8 m (generally 50-230 juveniles per collector) with peaks in August and December 1993 (April and June 93 at 19-21 m). The length-weigh mass relation was higher at 19-21 m, suggesting greater food availability because of lower organism density (including P. colymbus) and a greater water flux. Phytoplanktonic abundance and temperature were correlated (r2=0.38) with juvenile abundanc; this relationship and the association of juvenile abundance with higher temperature and Chlorophyll a levels, suggest that spat abundance was higher at the beginning of the water stratification period, when phytoplankton biomass is high.

The green mussel, Perna viridis, became widespread in the northern coast of Sucre State since its arrival to Venezuela in 1993. RNA/DNA and Protein/DNA ratios were used to study the effect of starvation on its instantaneous growth. The mussels were collected in La Esmeralda and Chacopata, acclimatized in the labo­ratory for four weeks and maintained for another six weeks in two groups: one fed ad libitum and another with­ out food (this later group was later fed for two additional weeks). Protein (colorimetric method), and nucleic acid concentrations (RNA and DNA, fluorometric method with ethidium bromide) were measured in adductor mus­cle, digestive gland and gills. The instantaneous growth was assessed using RNA/DNA and Protein/DNA rations. These indexes were always higher in the fed organisms. Animals from Chacopata were in better physiological condition that those from La Esmeralda during the abstinence time (six weeks). Muscle was the best tissue to determine instantaneous growth. The RNA/DNA ratio is a reliable index to determine the physiological condition and instantaneous growth of this species.

The study of otolith in larvae is important to determine fish age and growth, essential parameters in the study and management of fisheries resources. In this study, the formation of the hatching mark in Sardinella aurita was verified on ichthyoplankton samples collected off southern Cubagua island, Venezuela, from May 1998 to January 1999. The embryos were kept alive using a culture system until they hatched and daily a group of 10 to 30 larvae were fixed in 95% ethanol. An image analysis system was used to measure morphometric char­acteristics of larvae and sagittal otoliths. Following are mean values in newly hatched larvae: otolith hatching mark distance from nucleus 4.78 m (I.C 0.36 m, p 0.05 n= 30) increase width 1.46 m (I.C 0.17 μm, p 0.05, n= 30) and diameter 14.28 m (I.C 1.11 m, p 0.05, n = 30). The mean standard length of larvae at age O was 3.31 mm (I.C 0.08 mm, p 0.05, n= 200). The identification of the hatching mark allows the exact calculation of the number of rings in larvae from the natural environment.

Octopine dehydrogenase (Odh) was examined in several species of bivalves and gastropods and complemented with bibliographic data, to assess the controversy between neutralism and selectionism in explaining the maintenance of genetic variation in natural populations. This debate was the center of the molecular evolu­tion and population genetic research in the 1970s and 1980s, but waned thereafter, without resolution. Although DNA data have been produced, implications are not understood. We examined the polymorphims of Odh in sev­eral species of bivalves and gastropods, and the kinetic properties (apparent K,J of the different isozymes in the scallop Euvola ziczac that indicates an apparent case of overdominance of the heterozygous individuals. The question "which of the two hypothesis is correct" has shifted with time to "how much influence did each factor have in the maintenance of genetic variation".

Bauxite explotation of the Orinoco River in recent years is an important source of heavy metals discharge in the ecosystem, changing the natural biochemical flow of these elements and their concentrations in water, sediment and organisms. Iron and copper concentrations were measured in the fish Plagioscion squamo­sissimus in the Orinoco river, by sampling the fish population for three months (September-November 1998) in the main channel of the middle Orinoco (07°38'21.2" N; 66°19'10.9"W) and in Castillero lagoon (7°39'09"N; 66°09'00"W) with 2 and 4 cm mesh sizes. The internal organs of 30 fishes per month and site were stove­ dried at 80° C,pulverized and dried in disecator for 30 min to use as indicators with the acid digestion method for predicting the effect of heavy metals. We found relatively high values of iron and copper concentrations in fishes of the lagoon, and high seasonal variations in the iron concentration.

Benthic test species used in toxicity assays are the best indicators of sediment toxicity because they live in direct contact with sediments and the water column. Mercury chloride is one the most toxic metallfe salts. Its strong affinity for particles explains the high Hg content found in benthic populations. The genus Emerila is abundantly found in Venezuelan coasts and is a good bioaccumulator of pollutants, but the toxicological assays performend on this,genus ¡u-e scarce. The present experimental test reports on the distribution of mercury in the water column and sediment, using static bioassay in short term (24hr) and the ability of Emerita portoricensis lo bioconcentrate mercury under experimental conditions. Our resists suggest that the Hg transference from water to sediment is enhanced in the presence of Emerita. The kinetic uptake of Hg in Emerita portoncensisis shows a mechanism of rapid absorption reaching high metal concentrations in short exposure times.

The yield, gel strength, gelling and melting temperatures of Gracilariopsis tenuifrons agar from Guay­acán, Araya Peninsula, Sucre State, Venezuela were determined. Yield values with and without alkali treatment ranged from 23.22 to 39.57% and from 16.29 to 22.42% respectively, while gel strength with alkali treatment fluctuated betwen 699.31and 1231.69 g/cm2 and without treatment varied from 278.0 to 691.06 g/cm2. Gelling and melting temperatures were in the range reported for other agarophytes. Considering gel strength, the agar quality of G. tenuifrons was higher than in other species and its exploitation in economically feasible.

We studied the effect of slope variations on the structure of a reef community.Four sections of a reef char­acterized by different topographic slopes were studied. The sampling design was systematic,using the transections and quadrate methods to estimate the frequency, as well as total and relative coverage of the following substrata cat­egories: coral species, gorgonians, sponges, briozooans, dead coral and sand. Simultaneously the depth gradient for each section were measured. A total of 29 species of petreous corals was found. The dominant coral species was Montastrea annularis, followed by Colpophyllia natans, and Madracis mirabilis. An Importance Value Index was estimated for the different substrate categories on each section of the reef, taking into accountthe average relative coverage and the occurrence frequency. The Kendall correlation tests pointed out the existence of significative dif­ferences in the relative importance of these categories when similar zones of the studied sections were compared. The comparison between steep and intermediate slopes produced the biggest difference (82.24%, p=0.1529). Our results suggest that the slope variations within a same reef must be taken into account to establish the sampling design for the evaluation of community structure.