Flounder with partial intestine osmoregulate in seawater

Summer flounder (Paralichthys dentatus) that survived flounder infectious necrotizing enteritis (FINE) provided an unusual model for testing the role of the intestine in maintaining salt and water balance. The survivors lost 67% of the posterior-most intestine. The remaining stump of the anterior intestine healed and became a blind pouch. We sampled the fish three months after the epizootic ended, demonstrating that these fish survive with only a portion of their intestine. We hypothesized that salt and water balance would be disturbed in the survivors of FINE. However, plasma osmolality and concentrations of Na+, Cl-, and K+ were the same in intact flounder and those with only an intestinal stump. No compensatory changes in gill Na+, K+-ATPase activity were detected. The fish with intestinal stumps continued to feed, but their body weight was only 41% that of intact fish. Summer flounder can maintain salt and water homeostasis, but fail to thrive, using only one-third of their intestine

A versatile and sensitive tritium-based radioassay for measuring hydrogenase activity in aquatic sediments

Abstract We present a method for the measurement of hydrogenase (H 2 ase) activity in aquatic sediments. The assay is based on the H 2 ase-mediated isotopic exchange between dissolved molecular hydrogen (H 2 ) and water. A slurry of sediment material is incubated with a tritiated hydrogen (HT) headspace in a glass syringe on a rotary shaker. The method includes a procedure for preparing HT from radiolabeled sodium borohydride, which is a useful alternative to purchasing HT directly. A method for measuring HT specific activity based on liquid scintillation counting is also presented. Validation tests were run using live and frozen cultures of Clostridium pasteurianum and Desulfovibrio vulgaris, and freshly collected marine sediments. Adherence to Michaelis-Menten kinetics was demonstrated. An interassay coefficient of variation of 15% was determined using frozen C. pasteurianum cultures as reference material. Serial dilutions of cultures and sediments showed that measured H 2 ase activity scales with cell concentration, and indicate that the method can detect C. pasteurianum cell concentrations of between 300 and 3000 cells/ ml. This technique allows measurement of H 2 ase activity in a variety of environmental samples, and will be particularly useful in the study of deep marine sediments with low microbial activity

Oocyte development in summer flounder: Seasonal changes and steroid correlates

Seven ovarian stages are described in summer flounder Paralichthys dentatus. In the prespawning season plasma oestradiol levels increased in maturing fish with lipidogenic oocytes and gonadosomatic index increased in fish undergoing vitellogenesis. Atretic oocytes present in the postspawning season indicated which individuals may have spawned. The pattern of oocyte development is similar to that of other flatfishes and some teleosts. The summer flounder was unusual in having a long lipid uptake phase (oocyte diameter up to 301 μm) prior to any indication of vitellogenin (yolk protein) uptake. This information will be useful in the construction of an updated maturity schedule for the wild population. (C) 2000 the Fisheries Society of the British Isles

Vibrio harveyi: a significant pathogen of marine vertebrates and invertebrates

Vibrio harveyi, which now includes Vibrio carchariae as a junior synonym, is a serious pathogen of marine fish and invertebrates, particularly penaeid shrimp. In fish, the diseases include vasculitis, gastro-enteritis and eye lesions. With shrimp, the pathogen is associated with luminous vibriosis and Bolitas negricans. Yet, the pathogenicity mechanisms are imprecisely understood, with likely mechanisms involving the ability to attach and form biofilms, quorum sensing, various extracellular products including proteases and haemolysins, lipopolysaccharide, and interaction with bacteriophage and bacteriocin-like substances