Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Lipid and fatty acid composition of wild Almaco Jack Seriola rivoliana at two maturation stagesPublication . Fernandes, Igor; Nogueira, Natacha; Faria, Graça; Fernandes, Tomásia; Faria, Marisa; Cordeiro, NereidaAlmaco jack (Seriola rivoliana) is an emergent marine finfish that presents high market value. In order to study the feasibility of the exploitation of this marine resource for human consumption the evaluation of the nutritional characteristics of this species has attracted the attention of the scientific community. The lipid characteristics and fatty acid composition were evaluated in muscle, liver and gonad tissues of wild Almaco jack from Atlantic Ocean at two different maturation stages. According to results, the lipid content was found higher at pre-spawning stage (21.78 - 36.17%) and highest proportion being exhibited in the liver. Palmitic acid was predominant among the saturated fatty acids (35.42 - 47.80%) and oleic acid was detected as the main monounsaturated acid (25.26 - 36.55%). Higher amounts of ω3 polyunsaturated fatty acids (PUFAs) were identified in gonads of resting females, of which more than 84% was accounted by docosahexaenoic acid (12.62%). Muscle and liver of resting females presented the highest ω3/ω6 ratios. The Hypocholesterolemic/Hypercholesterolemic index was higher in gonads of both maturation stages (0.97 and 1.05). The results showed that wild Almaco jack at resting stage were a better source of oleic acid and ω3 PUFAs and that liver and gonads present good nutritional by-products.
- Age and growth of the blue jack mackerel, Trachurus picturatus Bowdich, 1825 (Pisces: Teleostei) off Madeira archipelagoPublication . Vasconcelos, Joana; Alves, Adriana; Gouveia, Elisabete; Faria, GraçaBetween 1984 and 1986, 630 pairs of sagitta otoliths were collected to determine the age and growth of the blue jack mackerel, Trachurus picturatus from Madeiran waters. The oldest specimen in this study was nine years old and the largest was 46 cm of total length (TL). The parameters of the von Bertalanffy growth curve were estimated for the whole period studied for all fish (L∞=42.32 cm, k=0.161 year-1, t0= -2.563 year; r2=0.743) for males (L∞=39.57 cm, k=0.194 year-1, t0=-2.282 year; r2=0.722) and for females (L∞=49.78 cm, k=0.114 year-1, t0=-3.052 year; r2 = 0.747). There was no significant differences in mean lengths (t–test, p>0,05) and in the von Bertalanffy growth curves (F test, p>0,05) between sexes. The validity of otolith readings for estimating age and growth was supported by results from backcalculation method. No significant differences were found in the Bertalanffy growth curves between direct reading of otoliths and backcalculation. Growth parameters estimated from backcalculated sizes-at-age were: for both sexes, L∞=48.28 cm, k=0.135 year-1, t0=-2.898 year and r2=0.999; for males, L∞=44.79 cm, k=0.143 year-1, t0=-3.207 year, r2=0.999; and females, L∞=44.63 cm, k=0.163 year-1, t0=-2.430 year, r2=0.999. The relationship between length and weight was calculated for all fish (Wt=0.00764Lt3.05746; r2=0.951), for males (Wt=0.01271Lt2.90807; r2=0.915) and for females (Wt=0.00604Lt3.12613; r2=0.948).
- First observations of hermaphroditism in the patellid limpet Patella piperata Gould, 1846Publication . Sousa, Ricardo; Henriques, Paulo; Vasconcelos, Joana; Faria, Graça; Riera, Rodrigo; Pinto, Ana Rita; Delgado, João; Hawkins, Stephen J.Hermaphroditism is thought to be an advantageous strategy common in marine molluscs that exhibit simultaneous, sequential or alternating hermaphroditism. Several species of patellid limpets have previously been shown to be protandrous hermaphrodites. The present study aimed to confirm whether this phenomenon occurs in Patella piperata. Transitional forms of simultaneous protandrous hermaphroditism were found in intermediate size classes of P. piperata, in Madeira (North-eastern Atlantic). Sequential hermaphroditism was confirmed after histological analysis. The overall sex-ratio was biased towards females but approached similar proportions in the larger size classes. Analysis of size at sex change showed that at a shell length of 36 mm 50% of the population probably have changed sex. The results reported confirm the occurrence of sequential hermaphroditism. These findings are of utmost importance to the understanding of the reproductive biology of this species with direct effect on management and conservation of this traditionally harvested limpet.
- Stock assessment of the blue jack mackerel, Trachurus picturatus, in the North-eastern AtlanticPublication . Vasconcelos, Joana; Sousa, Ricardo; Riera, Rodrigo; Delgado, João; Faria, Graça; Serrano Gordo, LeonelA total of 49,151 blue jack mackerel, Trachurus picturatus, (Bowdich) was collected in Madeira Island (North-eastern Atlantic) between 2002 and 2016 to evaluate pos sible influence of fishing on landings and reproductive parameters. A decreasing trend in the length composition was observed over the study period and length at first maturity decreased by 2.78 cm TL. Maximum yield per recruit decreased from 2002 to 2016 but the corresponding fishing mortality was constant (Fmax = 0.4/ year). Considering the fishing mortality level in 2016, it is evident that the stock may be exploited beyond its sustainability limit. Amendments of the purse-seine fishing regulations and implementation of measures to reduce fishing effort are suggested.
- Atlantic chub mackerel (Scomber colias) spawning season, size and age at first maturity in Madeira watersPublication . Vasconcelos, Joana; Afonso-Dias, Manuel; Faria, GraçaThe pelagic chub mackerel, Scomber colias Gmelin, 1789 is one of the most important fishery resources in the Madeira Archipelago. S. colias is caught by a small and coastal purse-seine fleet that traditionally operates around the islands. Monthly samples of chub mackerel were taken from commercial landings, between January 2002 and December 2005. Sex and maturity were assigned by visually inspecting the gonads of 1998 males (17.4-46.0 cm total length, TL; 0-5 yr) and 2108 females (18.0-41.2 cm TL; 0-4 yr) using a five-stages macroscopic maturity scale; 99 specimens with undetermined sex (13.0-26.8 cm TL; 0 yr) were also sampled. The analysis of monthly gonadosomatic indices and maturity stages proportions showed that gonad development started slowly in July-August and in creased in October-December, for males and females. Spawning took place between Janu ary-April peaking in February-March. Maturity ogives were fitted to the observed propor tions of mature males and females by using non-linear methods, to estimate size and age at first maturity: 22.12 cm TL at 1.05 yr for males and 21.55 cm TL at 0.82 yr for females.