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Calcium regulation in sturgeon is of special interest because they are a representative of the ancient fishes possessing mainly cartilaginous skeletons and a supposedly low calcium demand. The present study aimed to characterize the effect of a chronic absence of dietary calcium and the effect of parathyroid hormone-related protein (PTHrPA) (1-34) (7) on calcium balance in juvenile sturgeon (Acipenser naccarii). At rest, sturgeon juveniles are in net positive calcium balance, since whole body calcium uptake is significantly higher than efflux and calcium accumulates in the body. To study the importance of dietary calcium, the sturgeon were kept on a calcium-free diet for 8 wk. This manipulation impaired growth as measured by failure to gain weight or increase in length and indicates that dietary calcium is important for growth in sturgeon. An increased whole body calcium uptake partially compensated dietary calcium deficiency and was associated with increased gill chloride cell number in lamellae and filaments in parallel with increased gill [Na.sup.+][K.sup.+]ATPase activity. In addition, a single injection of piscine PTHrP(1-34) significantly increased whole body calcium uptake and decreased whole body calcium efflux. Administration of PTHrP significantly increased circulating plasma calcium 4-24 h postinjection. The increase in net calcium transport and increased plasma levels of calcium is consistent with the actions of a hypercalcemic factor. It would appear that the sturgeon rely on calcium for growth and tightly regulate calcium transport. The action in calcium balance is consistent with PTHrP acting as a hypercalcemic factor in sturgeon. chloride cells; fish; growth

Examines the ecophysiological adaptation to salinity throughout the life cycle of homarid lobsters. Variation of salinity tolerance during development; Use of behavioral strategies in avoiding low-salinity areas of larval and adult lobsters; Effect of low temperature on osmoregulation level.

Discusses a study which examined the crude homogenates and plasma-membrane-enriched fractions from the epithelium of the gills of epipodites and branchiostegites of European lobsters Homarus gammarus. Materials and methods; Results; Discussion and conclusion.

Background: Microcell parasites are small intracellular protozoans mostly detected in molluscs and can be associated with mortalities. In 2010 and 2011, strong increases in mortality events were reported in different wild beds of the wedge clam Donax trunculus Linnaeus, along the Atlantic coast of France and the presence of potential pathogens, including microcells, was investigated. Methods: Clams collected in different beds showing mortality were examined by histology. Based on histological observations, confirmatory analyses were carried out, including transmission electron microscopy (TEM) and molecular characterization. Results: Histological analyses revealed the presence of small protozoans similar to microcell parasites in different tissues of Donax trunculus, particularly in muscular and connective tissues. TEM examination confirmed the intracellular localization of the protozoans. Moreover, the lack of haplosporosomes and mitochondria suggested that the observed parasites belong to the genus Mikrocytos Farley, Wolf & Elston, 1988. Mikrocytos genus-specific PCR and in situ hybridization results supported the microscopic observations. Sequence fragments of the 18S rRNA gene shared 75–83% identity with the different Mikrocytos spp. described previously, including Mikrocytos mackini Farley, Wolf & Elston, 1988 and M. boweri Abbott, Meyer, Lowe, Kim & Johnson, 2014. Phylogenetic analyses confirmed that the microcell parasites observed in Donax trunculus in France belong to the genus Mikrocytos and suggest the existence of two distinct species. Conclusions: Based on morphological, ultrastructural, molecular data and host information, the two microcell parasites detected in Donax trunculus belong to the genus Mikrocytos and are distinct from previously described members of this genus. This is the first report of Mikrocytos spp. found in France and infecting the clam Donax trunculus. Mikrocytos veneroïdes n. sp. was detected in different wild beds and Mikrocytos donaxi n. sp. was detected only in Audierne Bay. [ABSTRACT FROM AUTHOR]