Fish predators

Performing Experiments. To test their hypothesis and prediction, the researchers captured several predator fish species and conducted the tests shown in Figure 1.8. The fish were presented with solitary sea butterflies, which they took into their mouths but promptly spit back out. The fish readily ate uncoupled amphipods but spit out any amphipod coupled with a sea butterfly. 

Reflect on Findings. These are the results expected if the sea butterfly was secreting some sort of chemical deterrent. The same results would be obtained, however, if the predator fish simply didn t like the feel of the sea butterfly in its mouth. The results of this simple test were therefore ambiguous. 

Performing Experiments. The researchers made one set of food pellets containing both fish meal and sea butterfly extract (the experimental pellets). For their control test, they made a physically identical set containing only fish meal (the control pellets). As shown in Figure 1.9, the predator fish readily ate the control pellets but not the experimental ones. The results strongly supported the chemical deterrent hypothesis. 

Make Observations. Further processing of the sea-butterfly extract yielded five major chemical compounds, only one of which deterred predator fish from eating the pellets. Chemical analysis of this compound revealed it to be the previously unknown molecule shown in Figure 1.10, which they named pteroenone. 

The predator fish (a) ate the control pellets but (b) rejected the experimental pellets, which contained sea-butterfly extract. 

There have been a few large-scale field studies of PCBs in the food webs of the lakes. These include two EPA mass balance studies, the Green Bay Mass Balance Study and the Lake Michigan Mass Balance Study. The field data collected for these studies was used to calibrate the complex contaminant models, which were developed as the primary goal of the studies. The ultimate objective of these mass balance studies was to predict concentrations of PBTs in top predator fish from only knowing the external loadings of the PBTs. Thus the models linked food web models to fate and transport, hydro-logic, and nutrient models. To calibrate the food web models, an extensive collection of all major trophic levels over both space and time was done and analyzed for PCBs and other selected analytes. 

Fig. 5 Spatial distribution of PCNs in sediment [118-120], predator fish [149], and air [63, 76,126] in the Great Lakes region. Bars represent maximum sediment concentrations (tri-octaCNs, ngg-1 dw), maximum fish concentrations (tri-octaCNs, ngg-1 ww), and mean air concentrations (tetra-octaCNs, pgnr3)...

There have been numerous measurements of PBDEs in fishes from the Great Lakes, and these data are summarized in Table 6. The concentrations range from 1000-3000 ng/g lipid for top predator fishes (such as trout and salmon) sampled recently down to 1-10 ng/g lipid for fish sampled in 1980. Taken as a whole, there is a strong relationship of concentration with time (see Fig. 5, note the logarithmic concentration scale), and this relationship holds... 

Fish and Wildlife. A survey of 2,3,7,8-TCDD contamination in benthic (bottom feeding) and predator fish from major U.S. watersheds was conducted for the EPA National Dioxin Study (Kuehl et al. 1989). It was observed that 17 of 90 (19%) samples collected at sites statistically selected by the EPA had detectable levels of 2,3,7,8-TCDD, whereas 95 of 305 (31%) samples from sites chosen by EPA regional laboratories had detectable levels (detection limits 0.5-2 ppt on a wet weight basis). Of the 112 sites where 2,3,7,8-TCDD was detected, 74 samples (67%) were below 5 ppt, 34 samples (32%) were between 5 and 25 ppt, and 4 samples (1%) were above 25 ppt. A subset of samples collected at sites near the discharges from pulp/paper manufacturing facilities (n=28) had a higher frequency of... 

Larvae of amphibions flee and hide in response to waterborne chemicals from predators (Kats et al. 1988 Kats 1988 Petranka et al. 1987). Run water through a flow-through system of four consecutive tanks from a water tank to a tank with predator fish, to a tank with tadpoles, and finally to a water tank. For the control experiment, there are no fish in the second tank. Observe and measure the spatial distribution and the shelter-seeking by the tadpoles under three conditions in the second tank is no fish a predatory fish and nonpredatory fish. 

Amouroux D., Donard O. F., Krupp E., Pecheyran C., Besson T., and Fitzgerald W. F. (2003) Isotopic fractionation of mercury species in top predators fishes (tuna and whale) from world ocean preliminary results. In Abstracts ofASLO Aquatic Sciences Meeting, Salt Lake City, UT, USA, 8—14 February. 

Most of the discrimination between inorganic and methylmercury thus occurs during trophic transfer, while the major enrichment factor is between water and the phytoplankton. This also has been reported for the diatom Thalassiosura weissflogii in a marine food chain (Mason et al. 1996). Methylmercury was accumulated in the cell cytoplasm, and its assimilation by copepods was 4 times more efficient than the assimilation of inorganic mercury. Bioaccumulation has been demonstrated for predator fish in both freshwater and marine systems and in marine mammals (see Section 5.4.4). Bioaccumulation of methylmercury in aquatic food chains is of interest, because it is generally the most important source of nonoccupational human exposure to this compound (EPA 1984b WHO 1990, 1991). 

Fig. 15.1. Relative frequency of predator fish selachian at the market of Fiume during and after WWI (data from Kot (2001)).

A deficiency in iodine causes goiter even in fish (thyroid hyperplasia, increased mortality) (Anonymous 1983). Polychlorinated biphenyls caused severe endemic goiter in predator fish in the Great Lake (USA) waters (Matovinovic and Trowbridge 1980). 

The accumulation of nnacceptable concentrations of mercury in fish occurs largely as a result of bioaccumulation of methyl mercnry np the food chain to the top predator fish, which are the most desired species. Methyl mercnry forms largely in the anaerobic sediments of water bodies and then moves up through several trophic levels. 

The Lotka - Volterra equations deal with the response of a biological population that is oscillating. Volterra observed that in some years the adriatic fishermen came back with a lot of fishes in their nets, and in some years there was a lack of fishes. Volterra attributed this that the fishes are predominately not the prey of the fishermen, but of other fishes. He concluded that the variations in the amount of prey fishes arise from the fact that the big (predator) fishes eat the small fishes. Therefore, the population of the big fishes is growing, but simultaneously the amount of small fishes is decreasing. 

Studies related to the occurrence of Hg in tissues of teleost fish are abundant, and geographic areas where levels of this metal in muscle exceed regulations for human consumers include Italy, Spain, Taiwan, Florida, and Oregon (Eisler 2010). It is notable that elevated concentrations of Hg do exist in top predator fish like marlins. Elevated Hg levels in muscle tissue were reported in the blue marlin Makaira nigricans 10.5 pg g- wet wt) collected from the northern Gulf of Mexico (Cai et al. 2007) and in the black marlin Makaira indica) from NE Australia (Mackay et al. 1975). 

In Mexico, as in other developing countries, there is a need to study the toxicological effect of mercury and others pollutants (Ydfiez et al. 2002). The main research areas that need attention as regards the effects of Hg on humans include (a) patterns of human consumption of predator fish species and Hg levels in the edible portion of these fish (b) levels of Hg in people occupationally exposed to this element (personnel who formulate dental amalgams, miners, workers in chloralkali plants, etc.) and (c) concentration of Hg in skin-lightening creams manufactured in Mexico. 

Fig. 9.4. The new mixed model for metals in lakes. Load (or dose) parameters are related to the input of metals to the lake (direct load and load from the catchment), the metal amount in the lake water is distributed into dissolved and particulate phases by the partition coefficient (Kd). Sedimentation is net sedimentation per unit of time (the calculation unit is set to 1 year for Hg and 1 month for Cs). The sensitivity parameters influence biouptake of metals from water to phytoplankton (but they may also be used in other contexts, e.g., to influence the Kd-values, as illustrated by the dotted line, or the rate of sedimentation). The biological or ecosystem variables include pelagic and benthic uptake, bioaccumulation and retention time in the five compartments (lake water, active sediments, phytoplankton, prey and predator fish). The ejfect parameter is the concentration of the metal in predatory fish (used for human consumption). One panel gives the calculation of concentrations, another the driving parameters (model variables should, preferably, not be altered for different lakes, while environmental variables must be altered for each lake). The arrows between these two panels illustrate the phytoplankton biomass submodel...

Sensitivity tests have been carried out to identify the most important model variables for calculations of the concentration of Hg and Cs in predator fish, and to illustrate how the model works. 

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