Prey 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... 

Mercuiy concentrations in prey fish are useful indicators of relative MeHg levels in food webs snpporting the prodnction of sport fish and wildlife, information relevant to the pnblic and the policy community. There is a sizable scientific literature on MeHg in prey fish, bnt they have been monitored less extensively than sport fish. Effects of removal sampling on target populations would be insignificant in all but the very smallest lakes. 

In summaiy, prey fish are present in most surface waters, require moderate sampling effort, are important in the trophic transfer of MeHg in aquatic food webs, and probably indicate annual changes in exposure to MeHg. Given these attributes. 

Example of a Prey-Fish Indicator Yellow Perch Analyses of total mercnry in whole bodies or axial muscle tissue of age-1 yellow perch have provided a useful measure of MeHg concentrations in food webs of many North American lakes. This widely distributed species inhabits lakes and reservoirs across mnch of the north-central, northeastern, and eastern United States and across the central and eastern provinces of Canada (Scott and Crossman 1973 Becker 1983). An ecologically similar congeneric species, the Eurasian perch Perea fluvi-atilis), is distribnted across much of Europe and northern Asia (Thorpe 1977). 

Criterion Importance of criterion Periphyton Phytoplankton Zooplankton invertebrates Prey fish fish L> 0... 

The second factor is the temporal variation in concentrations in different ecosystem compartments. For example, sediments and prey fish exhibit less temporal variation in mercuiy concentration than do air or water, and thus statistically valid estimates of their status can be collected with less frequent monitoring (e.g., annual sampling for prey fish vs. daily or hourly sampling for atmospheric concentrations of mercury). 

Northern pike (Esox lucius), an esocidae species, is considered one of the most widely distributed freshwater fish [57]. It is a piscivorous species, consisting its diet on common carp (Cyprinus carpio) and roach Rutilus rutilus). Nevertheless, in the absence of prey fish, invertebrate feeding could be important for this species [58, 59]. 

Monteiro, L.R., V. Costa, R.W. Furness, and R.S. Santos. 1996. Mercury concentrations in prey fish indicate enhanced bioaccumulation in mesopelagic environments. Mar. Ecol. Prog. Ser. 141 21-25. 

Prey fish may mask their own odors. Some marine fish avoid predation by covering their body odors. Some parrot fish (Scaridae) sleep in a mucus cocoon. It is believed that this covers up its scent and protects it from predation. Table 12.1 summarizes some chemical predator-prey relationships in marine fish. 

Table 12.4 Respones of prey fish to predator chemicals...

Fish avoid more vigorously the odor of predators that have fed on members of their species than that of those on different diets. For example, young Arctic chart avoid water from brown trout fed on Arctic chart and are less wary of that from pellet-fed trout (Hirvonen et ah, 2000). Prey fish also reduce their predator inspection behavior vis-a-vis predators that have eaten members of their own species. For instance, finescale dace, Phoxinus neogaeus, dash toward predators such as yellow perch, Percaflavescens, and withdraw. Dace inspect perch models less often if the model is accompanied by water from perch that had eaten dace than if accompanied hy water from perch on a swordtail, Xiphophorus hdleri, diet. Dace produce alarm pheromone, while swordtails do not. The Central American swordtails do not cooccur with finescale dace (Brown etal, 2001). 

Prey fish (pnmpkinseed and common shiner) responses to odors from predatory fish (rock and smallmonth bass)... 

Chivers DP, Zhao XO, Ferrari MCO (2007) Linking morphological and behavioural defenses Prey fish detect the morphology of conspecifics in the odour signature of their predators. Ethology 113 733-739... 

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. 

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

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