Piscivorous fish

Prey fish are here defined as small, usually short-lived, finfish. In North American fresh waters, many are members of the cyprinid (minnow), percid (perch), and centrarchid (sunfish) families. Prey fish are widely distributed, common, and important in the transfer of MeHg to higher trophic levels, such as piscivorous fish and many fish-eating birds. MeHg concentrations in prey fish of uniform age are less... 

Criterion Importance of criterion Periphyton Phytoplankton Zooplankton Benthic invertebrates Prey fish Piscivorous fish... 

For piscivorous fish, we recommend that axial muscle without skin be sampled and analyzed to avoid the additional variation that would result from differing proportions of skin and axial muscle tissue among samples. Concentrations of mercury are less in skin than in axial muscle, and the inclusion of skin in a filet can reduce the concentration of total mercury or MeHg in the sample by 5 to 12 percent (Glass etal. 1998 Serdaretal. 2001). 

In minnows, taste is not sufficient for predator recognition. Anosmic fathead minnows, P. pmmelas, did not show the flight reaction to the odor of northern pike, Esox lucius (Chivers and Smith, 1993). Naive European minnows, Phoxinus phoxinus, do not exhibit a fright reaction when first exposed to a predator odor, such as that of pike, E. lucius. They develop a conditioned fright response only after experiencing the predator odor in dangerous circumstances, such as when accompanied by schreckstoff (alarm pheromone) of conspecifics. Responses to the odor of non-piscivorous fishes such as tilapia, Tilapia mariae, can also be conditioned in this fashion but the responses are much weaker (Magurran, 1989). 

Ecological key(stone) species are species that play a major role in ecosystem performance, productivity, stability, and resilience. These species may also play an important role in ecosystem function (see below) and include 1) species that are critical determinants in trophic cascades, such as piscivorous fish and large herbivores and 2) species that are ecological engineers, that is, those that have a large influence on the physical properties of habitats such as rooted submerged macrophytes and beavers... 

Trophic level studies Indicated a decrease in Pu concentration with increase in trophic level (57). The CF values for benthic organisms and bottom feeding fishes were significantly higher than for piscivorous fish or for planktivorous fish ( v 1000 and 270 vs 4 and 20, respectively). Concentration factors derived from studies in a wide variety of freshwater and marine ecosystems are shown in Fig. 5. Invertebrates and algae exhibit higher CF values (10° - lO4) than fishes (0.0 - 50). The differences in CF values probably reflect differences in the source and chemical form of Pu at the various study sites. 

Increased algal growth, a decrease in piscivorous fish and a temporary increase in benthic and forage fish to the point where oxygen depletion results in overall decline and a decline in hypolimnetic oxygen concentrations in eutrophic lakes. 

In general, however, piscivorous fish show lower contents than non predatory fish depending on the species of adult fish selected and compared. 

Two general food webs can be conceptualized (i) a benthic sediment community which includes macroinvertebrates and (ii) a community that resides primarily in the water column, which includes phytoplankton and zooplankton as well as planktivo-rous and piscivorous fishes. For mercury species to accumulate within members of these food webs, they must be bioavailable and retained within the tissues. 

Diet, piscivorous fishes <100.0 p,g total mercury/kg fresh weight (FW) whole prey fish ... 

Brooks and Seegert (1977) suggested that indirect effects of exposure of fish to residual chlorine might increase mortality due to predation they observed that fish became lethargic when exposed to elevated levels of chlorine and thereby increased their vulnerability to piscivorous fish. 

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