Browsing by Author "Esteves, E."
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- Age and growth of the alfonsino, Beryx splendens, from the Azores (Berycidae)Publication . Aníbal, J.; Esteves, E.; Krug, H.; Silva, H. M. daThe Alfonsino, Beryx splendens Lowe, 1834, is a demersal fish species that inhabits the continental slope (200-600 m depth) in the eastern Atlantic (Quero, 1984) and seamounts around the islands of Madeira, the Canaries and the Azores (Maul, 1986). This species can also be found in the western Atlantic, Pacific and Indian Oceans (Bushakin, 1982 in Kotlyar, 1987). It is a bycatch of the Pagellus bogaraveo artisanal fishery in the Azores. The landings increased from 3 metric tons in 1980 (< 1% of the fishery landings) to 635 metric tons in 1994 (> 67%) (Lotaçor, 1980-1995). Available information on age and growth of Alfonsino from the Atlantic has come from fisheries sources and consists mainly of length-frequency, catch curves, age frequencies and length-at-age curves (Leon & Malkov, 1979; Kotlyar, 1987; ICES, unpublished report; Assessment Committee, 1995-1996; Gauldie, 1995). The objectives of this study were to determine the age from sagittae otoliths and to conduct a preliminarily growth study of the Alfonsino from the Azores.
- Are sardine larvae caught off northern Portugal in winter starving? An approach examining nutritional conditionsPublication . Chicharo, Maria Alexandra; Esteves, E.; Santos, A. Miguel P.; Santos, Antonina dos; Peliz, A.; Re, P.Recently, winter upwelling events off western Iberia have become more frequent. This may affect the production and survival of sardines egss and larvae through increased offshore transport. By analysis of RNA: DNA ratios, we investigated the impact of winter upwelling events on the larval conditions of Sardina pilchardus larvaeas a function of oceanographic conditions and food availability. Larvae were collected on a research cruise off northern Portugal in February 2000. Environmental parameters such as wind, water temperature, salinity microzooplankton biomass and daily egg production of the calanoid copepod Calanus helgolandicus also measured. The mean RNA:DNA ratios wererelatively high, indicating that almost all larvae collected were good condition. This was in agreement with the high microzooplankton biomass and high daily egg production of the copepod C. helgolandicus recorded during the same period. No adverse effects of upwelling causing offshore transport of larvae into poor feeding areas could be demonstrated because of the presence of a stratified warm plume with consequent high food production.
- Comparison of RNA/DNA ratios obtained with two methods for nucleic acid quantification in gobiid larvaePublication . Esteves, E.; Chicharo, Alexandra; Pina, T.; Coelho, M. L.; Andrade, José PedroIn this paper, RNA and DNA contents and RNA/DNA ratios obtained with two fluorometric methods for the extraction and quantification of nucleic acids in individual estuarine gobiid larvae are compared. A total of 141 gobiid larvae, collected in the Mira and Guadiana estuaries (Portugal), were analysed. This study indicated that the nucleic acids content and RNA/DNA ratios of individual larvae varied with the procedure used. The two methods yielded similar log DNA values but different log RNA and log (RNA/DNA). The differences could be due to a number of factors related to specific steps of tested protocols. Comparison of nucleic acids contents and calibration of the two methods by regression analysis provided a reasonable basis for comparison although differences between estimates were evident.
- Critérios de qualidade a observar no pescadoPublication . Esteves, E.; Aníbal, J.A qualidade dos produtos de pesca é, em grande parte, determinada pelo respectivo grau de frescura. Pretende-se, ainda, garantir que "o produto não afectará a saúde do consumidor quando processado e/ou consumido de acordo com o uso pretendido" - segurança alimentar.
- Ecology of the early life-history stages of shad Alosa fallax fallax (Lacépède, 1803) in the River Mira, with a note on Alosa spp. larvae in the River GuadianaPublication . Esteves, E.; Andrade, José PedroAllis and Twaite shad Alosa spp. are anadromous clupeid species, which still migrate into several rivers along Portugal to spawn but are regarded as Endangered or Vulnerable (using IUCN criteria). Within the framework of a countrywide research project, this dissertation reports the work carried out (from February 1998 until July 2000) to study the biology and ecology of the early life-history stages of Twaite shad, Alosa fallax fallax, in the River Mira (with a final note on Alosa spp. in the River Guadiana). Twaite shad larvae were more abundant in the surface waters during the day whereas no diel abundance pattern was observed for embryos (i.e. yolk-sac larvae). Furthermore, eggs, embryos and larvae were only found in the upstream stations of River Mira from late-March until mid- June. As expected, no habitat selection occurs at either the egg or embryonic life stages. Conversely, shad larvae abundances were related to several environmental co-variates through a complex non-linear generalised additive model (GAM). Paired translucent and opaque rings in a regularly-recurring sequence deposited around the sagittae of A. fallax fallax were readily visible. The high proportion of sagittae used suggests the usefulness of otolith microstructural analysis to estimate age and to study growth and morality of larvae. Growth and mortality rates varied seasonally (ranging from 0.36 to 0.60 mm d -1 and from 16 to 30 % d -1 , respectively). In a typical year, larvae are in better nutritional condition (RNA/DNA ratio) during two relatively short time-periods, around mid-April and mid to late?May when water temperatures average 22 ?C and levels of prey are <80 nauplii 100 m -3 . Conversely, RNA/DNA are significantly reduced when water turbidity is higher than 2 mg DW m -3 and potential prey are readily available (>20 nauplii 100 m -3 ). The few occurrences of Alosa spp. embryos and larvae in the River Guadiana and the tributary Ribeira de Odeleite precluded sensible analysis. Future topics of research to clarify some issues or directed at unanswered questions are proposed.
- Effects of alterations in fresh water supply on the abundance and distribution of Engraulis encrasicolus in the Guadiana estuary and adjacent coastal areas of south PortugalPublication . Chícharo, Luís; Chicharo, Alexandra; Esteves, E.; Andrade, José Pedro; Morais, P.A reduction of inflow to the Guadiana River on the border between Portugal and Spain may directly contribute to the degradation of fish habitats. Changes are expected to the spawning behaviour of Engraulis encrasicolus adults, to the migration patterns of larvae in the estuary, and to the catches of fisheries in the lower part of the river and adjacent coastal areas. Spawning of E. encrasicolus occurs in the lower part of the estuary and in the adjacent coastal areas. However, high abundances of larvae have been registered in the middle and upper parts of the estuary, the most productive region of the estuary, that with the estuarine turbidity maximum (ETM). In a year of normal inflow, such as the hydrologic year 1987-1988, some retention of larvae occured in this area. However, in an abnormal hydrologic year with a low inflow (1999-2000), and with an increase in freshwater inflow during the spring months, a disturbance to the migration pattern seems to have affected the survival of larvae in the estuary. High river flow, probably associated with an increased input of nutrients, appears to have important und positive effect on adult numbers, because anchovy fishery catches in the adjacent coastal area increased under these conditions.
- Effects of chilled storage on quality of vacuum packed meagre filletsPublication . Genç, Ísmail Yüksel; Esteves, E.; Aníbal, J.; Diler, AbdullahThe aim of this study was to experimentally assess several quality indices of meagre Argyrosomus regius (Asso, 1801) fillets packed in air (AP) and vacuum (VP) stored chilled (+4 C) for up to 13 days. Considering our experimental data on concentration of bacterial counts, shelf-life is estimated at ca. 6 days for AP fillets and an additional 3–5 days for VP meagre fillets. Total volatile basic nitrogen (TVB-N) and trimethylamine (TMA-N) did not reach the regulated limits (25–35 mg/100 g chilled fish). The models implemented in the software Seafood Spoilage and Safety Predictor predicted a relatively shorter shelf-life of 4.8–6.9 days for fish stored in air at +4 C when compared to AP and VP fillets. Empirical data and the models implemented in the software were used to predict the shelf-life of fillets if packaged under different modified atmospheres (MAP). Chilled, MAP fillets are likely to have a longer shelf-life than AP or VP samples if equilibrium CO2 concentration is substantially high.
- Effects of chilled storage, vacuum and modified atmosphere packaging on quality of meagre, Argyrosomus regius (Asso, 1801) fillets: a combined experimental and predictive approachPublication . Genç, I.; Esteves, E.; Aníbal, J.; Diler, A.Meagre, Argyrossomus regius (Asso, 1801), is a highly valuable commercial fish that has good marketing potential due to its size and shape.
- Effects of different thawing methods on the quality of meagre filletsPublication . Genç, Ísmail Yüksel; Esteves, E.; Aníbal, J.; Diler, AbdullahThe aim of this study was to determine the effect of different thawing methods (air, refrigerator, water and microwave) on physical, chemical and microbiological quality of meagre fillets which were frozen and stored at -20°C for 21 days. The samples were compared for colour changes, pH, total volatile basic nitrogen (TVB-N), hardness, adhesiveness, total viable count (TVC), total psychrophilic count (TPC) and hydrogen-sulphide producing bacteria (H2S). In terms of hardness, refrigerator thawed samples exhibited a harder texture compared to other ones. Taking into account all parameters studied, refrigerator thawing was found to be more suitable for the frozen meagre fillets.
- Effects of spoilage on nitrogen and carbon stable isotopes signatures of the clam Ruditapes decussatusPublication . Aníbal, J.; Veiga-Pires, C.; Esteves, E.Fish and seafood products are highly susceptible to post-mortem spoilage due to autolytic reactions at start, then microbiological activity and eventually oxidative reactions. Chemical and microbiological parameters are usually used to assess quality and make decisions for protecting public health, but they lack precision in defining which spoilage pathway is occurring at each moment. The objective of this work was to assess the effects of spoilage reactions on nitrogen and carbon stable isotopes in the grooved carpet shell clam, Ruditapes decussatus, and compare them to biochemical indicators of seafood deterioration, in order to better understand the relations between the different spoilage pathways during commercial storage conditions. Clams were kept in a refrigerator at 5 ºC, to simulate normal commercial storage conditions, and sampled in the beginning of the experiment, and after eight, ten and twelve days. Moisture, condition index, percentage edibility, total volatile basic nitrogen (TVB-N), pH, nitrogen and carbon percentages and stable isotopes were determined for each sampling moment. Stable isotope analyses were performed using a Costech Elemental Analyzer (ECS 4010) coupled to a ThermoFinnigan Delta V Advantage. Stable isotopes analysis, especially for nitrogen, proved to be a good tool for the study of clam deterioration. Nitrogen stable isotopes results showed a relation with other spoilage indicators, such as pH and TVB-N, and allowed identifying spoilage specific pathways, such as amino acids decarboxylation and production of volatile nitrogen compounds.
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