226Ra activity concentration in the mullet (Mugilidae) species Mugil cephalus whole individuals, and some organs (gills, gastrointestinal system, fins, muscle and bones), was measured by the γ-coincidence
spectrometer PRIPYAT-2M. 226Ra transfer parameters [concentration factors (CFs)] from seawater, sediment and mud with detritus to fish tissues, and annual
intake by humans consuming this fish species, have been estimated. Minimum detected radium activity concentration in whole
M. cephalus individuals was found to be 0.89 ± 0.42 to 3.09 ± 0.41 Bq kg−1, with arithmetic mean of 1.65 ± 0.39 Bq kg−1. An average concentration in muscles is found to be 2.28 ± 0.84 Bq kg−1, in gills—5.02 ± 1.85 Bq kg−1, in gastrointestinal system—12.88 ± 1.71 Bq kg−1, and in bones—14.72 ± 3.75 Bq kg−1. No one fins showed radium activity above minimum detectable one. Annual intake of 226Ra by human consumers of this fish species is estimated to provide an effective dose of 0.006 mSv year−1. CFs for 226Ra indicating transfer from seawater to whole individuals ranged from 8.9 to 30.9, and those indicating transfer from the
sediment and mud with detritus—from 0.11 to 0.39 and from 0.08 to 0.3, respectively. The seawater to bones CFs varied from
97.9 to 197.3, to gastrointestinal system—from 59 to 178.8, to gills—from 22.5 to 68.3, to muscles—from 17 to 30.8.
Authors:A.F.S. Garcia, A.M. Garcia, S.R. Vollrath, F. Schneck, C.F.M. Silva, Í.J. Marchetti, and J.P. Vieira
Food partitioning among coexisting species in different habitats remains an important research topic in trophic ecology. In this work, we combined carbon and nitrogen stable isotope ratios and stomach content analyses to investigate differences in diet and niche overlap of two congeneric juvenile mullet species (Mugil curema and Mugil liza) coexisting in a marine surf-zone and an estuarine zone in southern Brazil (29oS). These habitats have contrasting levels of food availability, especially in terms of prey diversity, with higher microalgae diversity in the estuary than in the marine surf-zone. In these contrasting conditions, we predicted that both mullet species will have (a) higher niche overlap and smaller niche breadth at the marine surf-zone due to the common exploration of highly abundant surf-zone diatoms and (b) lower niche overlap and higher niche breadth inside the estuary due to selective feeding on more diverse food resources. Isotope niche areas (measured as standard ellipse areas) were higher in the estuary (6.10 and 6.18) than in the marine surf-zone (3.68 and 3.37) for both M. curema and M. liza, respectively. We observed an overlap of 52% in isotopic niches of both species in the marine surf-zone and none in the estuary. We also found contrasting patterns in the diet composition between species according to the habitat. At the marine surfzone, diatoms of the classes Bacillariophyceae and Coscinodiscophyceae dominated (> 99%) the food content of both mullet species. In contrast, green algae, cyanobacteria, dinoflagellates and flagellates comprised the diet of both species in the estuary. These results could be explained by spatial differences in food availability (especially regarding diversity of microalgae) between both habitats. At the marine site, both species explored the most abundant microalgae available (mostly the surf-zone diatom Asterionellopsis cf. guyunusae and fragments of Coscinodiscus), whereas in the estuary both species shifted their diets to explore the greater diversity of microalgae resources. Overall, our findings revealed that niche partitioning theory could not fully predict changes in breadth and overlap of food niches of estuarine dependent fish species with complex life cycles encompassing marine to estuarine systems with contrasting food availabilities.
232Th activities in the South Adriatic Sea-water, surface sediment, mud with detritus, seagrass (Posidonia oceanica) samples, and the mullet (Mugilidae) species Mugil cephalus, as well as soil and sand from the Montenegrin Coast, were measured using the six-crystal spectrometer PRIPYAT-2M, which
has relatively high detection efficiency and a good sensitivity, and allows a short acquisition time, and measuring samples
of any shape, without preliminary preparation and calibration measurements for different sample geometries. An average 232Th activity concentration in surface soil layer is found to be 40.33 Bq kg−1, while in sand—4.7 Bq kg−1. The absorbed dose rate in air due to 232Th gamma radiation from surface soil layer ranged from 11.76 to 63.39 nGy h−1, with a mean of 24.06 nGy h−1. Corresponding average annual effective dose rate has been found to be 0.03 mSv y−1. The absorbed dose rates due to the thorium gamma radiation in air at 1 m above sand surface on the Montenegrin beaches have
been found to be from 0.41 to 9.08 nGy h−1, while annual effective dose rates ranged from 0.0005 to 0.011 mSv y−1. 232Th activity concentration in seawater ranged from 0.06 to 0.22 Bq L−1, as in the mullet (Mugil cephalus) whole individuals from 0.63 to 1.67 Bq kg−1. Annual intake of 232Th by human consumers of this fish species has been estimated to provide an effective dose of about 0.003 mSv y−1.
Authors:Á. Staszny, Enikő Havas, R. Kovács, B. Urbányi, G. Paulovits, Dóra Bencsik, Á. Ferincz, T. Müller, A. Specziár, Katalin Bakos, and Zs. Csenki
, A. L., Cowx, I. G., O’Higgins, P. (2007) Geometric morphometric analysis of fish scales for identifying genera, species, and local populations within Mugilidae . Can. J. Fish Aquat. Sci. 64, 1091–1100.
Authors:N. Nikolic, J.-L. Baglinière, C. Rigaud, C. Gardes, M. L. Masquilier, and C. Taverny
, Acipenseridae, Osmeridae, Clupeidae or Mugilidae, have been exploited by fishing at variable intensity in relation to the spatial and temporal evolution of stocks, the techniques used and the tastes of “consumers” (McDowall 1988 ). Harvest has strongly