Predatory fish

Another contaminant of concern for the Delta is Se. Selenium occurs in high concentrations in the soils of the western San Joaquin Valley associated with salts that have accumulated in this region [10]. Selenium is recycled through agricultural retom flows to the river and transported to the Delta and San Francisco Bay. The Se is transformed into a more bioavailable form by microbial communities and aquatic plants. The Se is passed through the foodweb with particular concern for bottomfeeding migratory waterfowl and predatory fishes. The hydrodynamics of water from the San Joaquin River is an important consideration in the intensity and distribution of Se contamination within the Delta. 

Johnston TA, Leggett WC, Bodaly RA, Swanson HK. 2003. Temporal changes in mercury bioaccumulation by predatory fishes of boreal lakes following the invasion of an exotic forage fish. Environ Toxicol Chem 22 2057-2062. 

A repetition of in situ experiments with the yellowhead wrasse, partially in response to the above criticisms, again showed that fish developed a learned aversion to otherwise palatable food that had been adulterated with 15P-PGA2 [99], This was presumably due to the emetic properties of PGA2. It was pointed out that methyl esters of prostaglandins are also known to possess emetic properties [104], and reasoned that if the 15-acetoxy ester inhibits the emetic properties of PGA2, then it is likely to be quickly lost because of its known lability, especially in the presence of coral esterase. Further, the acidic environment in the stomachs of predatory fish would promote hydrolysis of these labile esters. 

Based on the above investigations, it appears likely that prostaglandins in P. homomalla function to inhibit feeding by predatory fish. However, determination of the mechanism of their release and the degree of esterification in the ecologically active substance await further investigation. 

Health advisories have been issued near Lawrence, Kansas, based on chlordane levels in edible fish tissues. In fish from the Kansas River, Kansas, in 1986, chlordanes were detected more frequently and at higher levels than other contaminants measured (Arruda et al. 1987). More than 80% of the sites sampled in Kansas had detectable chlordanes in fish at more than 50% of these sites, levels exceeded 0.1 mg/kg fresh weight — a guideline for the protection of predatory fish. At three urban sites in Kansas, concentrations of chlordanes in fish have approached or exceeded... 

One amphipod that lives as plankton in the frigid antarctic is a creature called Hyperiella dilatata. This little creature is about 2 millimeters long and has the ill-fated distinction of being a favorite food for several common plankton-eating antarctic fishes. Unlike some of its relatives, Hyperiella has no spines or other physical features that might discourage predatory fish, nor does it possess any compounds suitable for chemical defense. 

Predatory fish may also be affected by alarm pheromones (Section 7.2) of the prey, both directly and indirectly. The alarm odor may act as defense compoimd that inhibits predator attack or reduces capture rate by inducing predator avoidance in school members of the prey species. 

Aposematically colored, the yellow-bellied sea snake, Pehmis platurus (Hydrophiidae), of the eastern Pacific has venom and is distasteful. It has no known aquatic predators, although remains were found in murray eels and sharks. Predatory fish such as snappers refuse the snake. They reject its meat even when hidden in palatable squid. Predatory fish of the Atlantic ocean, however, ate the sea snake in experiments, and died after 1 of 12 meals (Rubinoff and Kropach, 1970). 

Petranka, J. W., Kats, L. B., and Sih, A. (1987). Predator-prey interactions among fish and larval amphibians use of chemical cues to detect predatory fish. Animal Behaviour 35, 420-425. 

In McClintock and Baker s initial experiment, a predatory fish (a) rejected the sea butterfly, (b) ate the free-swimming amphipod, and (c) rejected the amphipod coupled with a sea butterfly. 

Wilson DM, Puyana M, Fenical W, Pawlik JR (1999) Chemical Defense of the Caribbean Reef Sponge Axinella corrugata Against Predatory Fishes. J Chem Ecol 25 2811... 

Many hydrophobic organic contaminants pose a threat to human health because they bioaccumulate to high concentrations in predatory fish that are eaten by people. From a human health standpoint, there is little concern of... 

Phytoplankton I Zooplankton Fish eggs and larvae Soft-bottom benthos Hard-bottom benthos Bottom fish Predatory fish Plant life Wetlands and estuaries Amphibians/reptiles Mammals Birds Water quality Human health... 

In nature, fish apparently acquire polyunsaturated lipids in one of two ways. The first of them conforms with the concept of Saigent and Henderson (1980), Watanabe (1982) and Henderson et al. (1985), that some species of fish do not need to synthesize long-chain polyenoic acids, since they occur in phytoplankton, which are eaten by zooplankton which in turn are food for fish. Takahashi et al. (1985) described the situation as unsaturated fatty acids being transferred from plant organisms to phytoplankton-eating fish to predatory fish. 

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