Crustaceans, conductivity

The first study was designed to assess the suitability of various microscale bioassays and recommend an appropriate testing strategy for sediment toxicity assessment (Cote et al., 1998a,b). The recommended test batteries included seven micro-scale laboratory assays conducted on bacteria (Vibrio fischeri), cnidarians (Hydra attenuata), micro-crustaceans (Thamnocephalus platyurus), and benthic macroinvertebrates (Hyalella azteca and Chironomus riparius), and involved two phases of exposure (pore water and whole sediment). A total of 16 stations were included in the toxicity assessment scheme. 

Many marine species also possess the tyrosinase-mediated pathway to synthesize the UV-absorbing pigment melanin. Melanin occurs in a wide range of taxa including bacteria, fungi, invertebrates, and chordates. While much is known about the role of melanin in the UV protection of mammalian skin, very little research has been conducted to examine the efficiency of melanin as a UV-protective mechanism in aquatic taxa.9 It is known that melanin levels in juvenile hammerhead sharks, Sphyrna lewini, are directly correlated to solar UV exposure in the freshwater crustacean Daphnia pulex, melanin concentrations are genetically determined within populations and are correlated to UV sensitivity.50-51 The few studies that have been undertaken suggest that melanin has an important role in UV protection in aquatic environments. 

The crustacean toxicity test to assess the mortality of T. platyurus was conducted by hatching these anostraca from cysts after 20-22 h of incubation at 25°C in the same synthetic freshwater used for rotifers and at the same illumination conditions. The test solutions in five concentrations (two-fold dilutions) with three replicates of 10 animals were poured in disposable multiwell test plates (1 mL per well). After 24 h in a 25 °C incubator in the dark, the number of dead crustaceans was recorded. 

However, some evidence of a significant electrical conductance in biomaterials was already available in the 1960s. For example, significant conductance was found (Digby, 1965) in crustaceans. Indirect support also came from mechanisms involving electron flow which seemed necessary to explain phenomena in photosynthesis, in enzyme reactivity, and in the energy-producing activities in mitochondria. 

The major food producing crustaceans that are presently aquacultured are various shrimp species, crayfish and lobsters (77). Pharmacokinetic studies of drugs have been done so far only in the lobster, but studies of the pharmacokinetics and metabolism of some agricultural chemicals have been conducted in crab and crayfish species. 

The past two decades have seen enormous advances in our understanding of crustacean chemical communication. Nevertheless, our knowledge is still in its infancy when compared to insects, fish, or mammals. Most research on crustacean behavior in response to chemical stimuli has been conducted in controlled laboratory environments, where often only one stimulus context is tested. For example, the responses of numerous crustacean species to chemicals emitted by potential mates, by conspecific aggressors, or by interspecific enemies have been tested in... 

In support of these observations on alterations in neuromuscular activity, experiments were conducted on lobsters using 20E injections. Bolingbroke and Kass-Simon (2001) observed that intermolt females injected with 20E displayed increased aggressiveness relative to saline-injected controls. These experiments on the effects of ecdysteroids on crustacean behavior are especially relevant to the discussion of these hormones as possible pheromones and allelochemicals later in this chapter. 

Several large-scale mesocosm studies were conducted with esfenvalerate, the most active form of fenvalerate. These investigators demonstrated that (1) the half-time persistence of fenvalerate in the water column is about lOh (2) initial concentrations of 1.0 or 5.0p.g/L were not detectable in the water column after 2 and 4 days, respectively (3) in the first 2 days after application the water column contained the majority of the fenvalerate (4) by day 4 postapplication, the sediments and macrophytes were the major reservoirs of fenvalerate (5) fish usually contained less than 1% of the esfenvalerate at any time (6) sensitive species of some copepod and insect genera showed declines in abundance at 0.08-0.2 p,g/L and were unable to recover (7) most species of zooplankton and benthic invertebrates decreased in abundance at 0.25 xg/L and higher (8) and finally, at 1.0-5.0 xg/L, there were drastic reductions or elimination of most species of crustaceans... 

A study of the uptake and release of inorganic phosphorus by the plankton crustacean, Daphnia magna, was conducted by Rigler (1%1). Groups of the organism were immersed for various periods of time in artifically prepared water... 

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