Evaluating prey capture by larval mummichogs (Fundulus heteroclitus) as a potential biomarker for...

transcript

Evaluating prey capture by larval mummichogs(Fundulus heteroclitus) as a potential biomarker

for contaminants

Judith S. Weisa, Jennifer Samsona,1, Tong Zhoua,2,Joan Skurnickb, Peddrick Weisc,*

aDepartment of Biological Sciences, Rutgers University, Newark, NJ 07102, USAbDepartment of Preventive Medicine and Community Health, UMDNJ–NJ Medical School,

Newark, NJ 07101-1709, USAcDepartment of Radiology (G-621), UMDNJ- NJ Medical School, P.O. Box 1709,

Newark, NJ 07103-1709, USA

Abstract

We evaluated larval prey capture as a ‘‘behavioral biomarker’’ of contamination by exam-ining feeding behavior of larval mummichogs (Fundulus heteroclitus) from many differentsites, including a severely contaminated ‘‘Superfund’’ site, moderately contaminated sites, and

reference areas. Prey capture ability was related to sediment contaminant levels. The levels ofcontaminants at a site were highly correlated with each other, so that the impact of individualcontaminants was confounded. The number of captures of brine shrimp by mummichog lar-

vae from all sites was highly variable, but significant negative correlations of prey capturewere seen with mercury, lead, zinc, cadmium, and PCBs. As observed previously with adults,polyaromatic hydrocarbons (PAHs) did not appear to impair prey capture ability. The only

site in which prey capture rates of 8-day old larvae were severely affected was the most highlycontaminated Superfund site, Berry’s Creek, NJ. This implies that larval prey capture is not assensitive a behavioral biomarker for contamination as adult behavior studied previously.

Keywords: Behavior; Biomarker; Fundulus; Larva; Mummichog; Population; Prey capture; Sediment;

Sublethal

Marine Environmental Research 55 (2003) 27–38

www.elsevier.com/locate/marenvrev

PI I : S0141-1136(02 )00204 -0

* Corresponding author. Tel.: +1-973-972-4409; fax: +1-973-972-7489.

E-mail address: weis@umdnj.edu (P. Weis).1 Present address: National Marine Fisheries Service, Sandy Hook, NJ 07732, USA.2 Present address: Food and Drug Administration, Centre for Food Safety & Applied Nutrition, 200 C

St., Washington, DC 20204, USA.

1. Introduction

Contaminants can alter behavior, including predator–prey interactions, which canhave effects on food webs. Atchison, Henry, and Sandheinrich, (1987) reviewedeffects of metals on fish behavior and emphasized that studies should have ecologicalrelevance. Reduced feeding is a common and ecologically relevant response to con-taminants, leading to reduced energy intake. Energy budget models can predict theconsequences of such reductions at the population level (Maltby, 1999). Impairedfeeding behavior of fish in laboratory experiments has been noted in response toexposure to sublethal concentrations of various pollutants (Little, Archeski, Flerov,& Kozlovskaya, 1990; Morgan & Kiceniuk, 1990; Scherer, McNicol, & Evans,1997), and can be related to impaired growth and population declines (Weis, Smith,Zhou, Santiago-Bass, & Weis, 2001).Pollutants may impair feeding behavior by affecting the motivation to feed and/or

by reducing the ability to capture prey. Little et al. (1990) noted that the frequencyof strikes was less sensitive to certain toxicants than the actual prey capture, indi-cating that coordination was impaired. However, Brown, Johansen, Colgan, andMathers (1987) found that PCP-treated fish performed fewer feeding acts, reflectingdecreased motivation to feed. Bryan, Atchison, and Sandheinrich (1995) notedreduced strikes in Cd-exposed bluegills. Prey handling time can be increased bytoxicant exposure, and can contribute to lower feeding rates (Sandheinrich & Atch-ison, 1989). Contaminants can also alter predator avoidance by prey species (Kraus &Kraus, 1986; Lefcort, Ammann, & Eiger, 2000; Smith &Weis, 1997). By altering preycapture and predator avoidance, pollutants can cause changes in predator–preyinteractions, resulting in population changes.The mummichog, Fundulus heteroclitus, is a very abundant estuarine fish that

consumes primarily crustaceans and annelids as adults, and feeds on the marshsurface at high tide. Previous studies (reviewed in Weis & Weis, 1989b) demon-strated differences between mummichog populations from clean reference areas andfish in contaminated areas, notably Piles Creek (PC), a polluted tributary of theArthur Kill in Linden NJ. Surrounded by industrial sites, a sewage treatment plant,a power plant and a major highway, the sediments and biota of this creek have ele-vated concentrations of many contaminants including mercury (Eckenfelder Inc.,1991; Khan & Weis, 1993). The PC fish have a reduced growth and shorter lifespan(Toppin, Hcber, Weis, & Weis, 1987) compared with those from cleaner sites ineastern Long Island NY (LI) and Tuckerton NJ (TK). This species has a very lim-ited home range (Lotrich, 1975) and would be expected to remain in the same systemthroughout its life.The reduced growth of PC fish is associated with reduced prey capture ability. The

PC adults were poor predators compared with those from TK (Smith & Weis, 1997),and PC fish, being generally ‘‘slow’’, had lower spontaneous activity and were alsomore vulnerable to predation by blue crabs than TK conspecifics (Smith & Weis,1997). The poor predation by PC adults was correlated with elevated brain mercury.When TK fish were maintained in an aquarium with PC sediments and water andfed PC grass shrimp, their prey capture ability declined in 1 month to that of PC

28 J.S. Weis et al. /Marine Environmental Research 55 (2003) 27–38

fish, and their brain mercury concentrations increased to that of the PC fish. WhenPC adults were maintained in clean water for 2 months, there was only a slightimprovement in their prey capture ability, and brain mercury (Hg) did not decrease(Smith & Weis, 1997). This correlation of behavior with brain Hg does not neces-sarily mean that Hg causes the altered behavior; other contaminants may also con-tribute, since there are many contaminants at PC. In polluted aquatic systems, it isgenerally difficult to establish causal relationships between particular contaminantsand effects, because of the multitude of interacting environmental factors.Larval stages of fish are especially sensitive to contaminants (Weis & Weis, 1989a),

but there have been relatively few studies on contaminant effects on their behavior.Neurological development during embryonic life can be affected by contaminants,and can have effects on behavior after hatching (Samson, Goodridge, Olobatuyi, &Weis, 2001; Weis & Weis, 1995a,b). As fish larvae have a limited ability to withstandstarvation, effective prey capture is essential for their survival. Reduced feedingbehavior may reduce growth and prolong larval development, which may in turnincrease predation risk and decrease survival. Embryonic exposure to methylmer-cury had effects on larval prey capture in mummichogs (Weis & Weis, 1995a),although these effects were transitory if larvae were raised in clean water (Zhou,Scali, & Weis, 2001). Comparing PC and reference larvae shortly after hatching, PClarvae were better at prey capture and predator avoidance than reference larvae, butlater they became poorer at both (Zhou & Weis, 1999).‘‘Biomarkers’’ are responses measured in organisms that can provide information

about exposures to contaminants or sublethal effects resulting from such exposures.Most biomarkers, such as metallothioneins, cytochrome P-450, and heat shockproteins are at the biochemical or cellular level of biological organization; thus theirlinks to population level effects are difficult to establish. If altered behavior shouldprove to be a useful biomarker, its links to population level effects are much moreapparent and direct. Considering prey capture as a ‘‘behavioral biomarker’’ of con-taminant effects, we previously examined feeding behavior of adult mummichogsfrom many different sites, including some severely contaminated ones as well asreference areas, and correlated the prey capture ability with sediment contaminantlevels (Weis, Samson, Zhou, Skurnick, &Weis, 2001b). We were able to obtain larvaefrom most of these populations. The primary exposure of these larvae would havebeen through the mother rather than directly from the environment. In this paper,we report the relationships of larval prey capture ability with site contamination.

2. Materials and methods

Adult fish were collected using Gee’s minnow traps, and sediments were collectedat the following sites:

� Sandy Hook NJ (SH): the entrance to Raritan Bay;� Newark Bay NJ (NB): highly contaminated urban estuary in northern NJ;

J.S. Weis et al. /Marine Environmental Research 55 (2003) 27–38 29

� Piles Creek NJ (PC): highly industrialized creek off the Arthur Kill in LindenNJ;

� Vince Lombardi Rest Stop NJ (VL): in northern part of the contaminatedHackensack Meadowlands, adjacent to the NJ Turnpike;

� Union Beach NJ (UB): along the southern end of Raritan Bay;� Berry’s Creek NJ (BC): Hg Superfund site in the Hackensack Meadowlands;� Bullhead Bay NY, (BB): relatively clean site in Southampton NY, previouslyused as a reference site, though near a golf course;

� East Hampton NY (EH): cleaner reference site in Long Island NY; and� Tuckerton NJ (TK): cleaner reference site in southern NJ.

2.1. Contaminants

2.1.1. SedimentsSediment samples of the top 5 cm in shallow subtidal areas from each of the sites,

two replicates per site, were collected in nitric acid-washed polycarbonate jars andstored at 4 �C until analysis. They were dried, weighed, and extracted with 3:1 nitricacid/perchloric acid reagents (‘‘for trace metal analysis’’) at 70 �C for 24 h. Theextracts were analyzed for total cadmium, lead, copper and zinc by atomic absorptionspectrophotometry (AA) by flame absorption in a Perkin-Elmer model 603 instru-ment. For total mercury analyses, cold vapor AA methods of Hatch and Ott (1968)were used: 4:1 H2SO4/HNO3 extraction, KMnO4 oxidation overnight, NH2OH.HCland SnCl2 reduction, measurement in a Bacharach MAS-50D instrument.Quality assurance for the metal analyses involved simultaneous analyses of

National Institute of Standards and Technology (NIST) standard reference materialSRM 1645 (Estuarine Sediment) for sediment analysis as well as method blanks. Onereference material and one blank was included with each of 12 samples. Acceptabilityof data for a run required the reference data to be within the 95% confidence limit;this requirement was usually met. Acid-washed glassware, deionized/distilled water,and reagents ‘‘for trace metal analysis’’ were used throughout. In addition to thedata we collected, we utilized existing sediment data on organic contaminants [PCBsand polyaromatic hydrocarbons (PAHs)], collected at or near these sites by otherinvestigations, such as the EMAP (Environmental Monitoring and AssessmentProgram) of EPA (Adams, O’Connor, & Weisberg, 1998; Eckenfelder, Inc., 1991).Adult livers were also analyzed for metals and these data are reported in Weis,Samson et al. (2001).

2.2. Larval prey capture

Eggs and milt were stripped from multiple ripe females and males into petri dishesand were fertilized in the field in site water. They were brought back to the labora-tory where successfully fertilized eggs were subsequently washed and transferred to8.5-cm finger bowls with 50 ml artificial sea water (15 ppt, Instant Ocean1 sea salts)at 22 �C. Three replicate dishes were used for each population. Water was changed

every 2 days. To ensure daily synchronous hatching, the developed embryos fromday 14 onward were exposed to air for about 1 h and then re-immersed in water.Hatched larvae were also kept in finger bowls with 50 ml sea water at a density ofone larva per 5 ml solution.At hatching, larvae were kept in clean filtered sea water and fed brine shrimp

(Artemia salina) nauplii daily after the initial prey capture test. [Brine shrimp are nota normal part of the diet, but are easily cultured and of the appropriate size forfeeding early larvae. They are a modest challenge for catching, since not every strikeentails capture, and the number of strikes per capture increases after lab exposure tomethylmercury (Zhou et al., 2001). Normally at testing age the larvae eat anythingsmall that moves.] They were tested for prey capture at three days (when feedingbegins) and again at 8 days post-hatch. The test consisted of placing five brineshrimp nauplii in 3 mm deep artificial seawater in a small glass dish, then adding onelarva. The time of each capture was recorded over 5 min. At least 30 larvae fromeach population, from the different replicate dishes were tested, and different indi-viduals were tested on days 3 and 8. The number tested for each population are asfollows: SH—60, NB—31, TK—60, PC—60, VL—60, BC—50, UB—60, EH—30,and BB—30.

2.3. Statistical analysis

Predation behavior was summarized by site as mean number of captures per trial.The observed distributions of contaminant levels in sediment were plotted, andbivariate linear and Spearman rank correlations among contaminants and predationbehaviors were computed. Correlations among sediment contaminants were expres-sed as Pearson linear correlation coefficients, with one measurement per site. Whenindicated by preliminary plots, contaminant measurements were transformed to alog scale; a log value one-half the next smallest value was imputed to zero values.The number of captures was treated as a Poisson variate. Analysis of variance(ANOVA) was performed to compare sites, after square root transformation ofcaptures, to normalize and stabilize the variance of the Poisson variate. Tukey’sadjustment for multiple comparisons was used. The association of contaminantswith captures was analyzed by Poisson regression using the GENMOD SAS proce-dure, with estimates and P-values adjusted for overdispersion (greater within-sitevariability in responses than a simple Poisson variable.) Generalized coefficients ofdetermination (rG) were used to express the degree of correlation between capturesand contaminants, following Nagelkerke’s procedure (SAS Institute, 1997) andincorporating multiple observations per site. Multivariate models were explored toexplain capture behavior in terms of joint effects of contaminants. However,these models did not produce useful explanatory combinations, and thus theresults are not presented. Statistical analyses were performed using Statistix1

and SAS software packages. The level of significance was 0.05. Correlationspresented as sets of contaminants (five metals, two organics) were considered sig-nificant if P<0.01 (approximate adjustment for experiment-wise error by Sidak’smethod).

3. Results

3.1. Contaminants in sediment

The levels of Hg, Cu, Pb, Zn, and Cd in the sediments are presented in Table 1.The table also includes the Long, MacDonald, Smith, and Calder (1995) ERL(effects range—low) and ERM (effects range—medium) values, for reference. Theseranges represent sediment levels of particular contaminants that would be expectedto have either low or moderate effects on benthic organisms (Long et al., 1995). Thelevels of contaminants at a site were highly correlated with each other, so that theimpact of individual contaminants was confounded, regardless of how the beha-vioral outcomes were modeled. It can be seen that the sites considered contaminatedhave a suite of contaminants. Even some of the sites considered clean (BB and TK)exceed the ERL values for some metals. Only EH does not have contaminant levelsexceeding the ERL values. The highest value of Hg by far is in BC, the Hg-Super-fund site. The next highest concentration is at PC, which is an order of magnitudehigher than all the remaining sites. The lowest values are seen at EH, which is anorder of magnitude lower than the next group, which includes BB, SH, and UB. Thehighest sites for Cu concentrations are BC, NB, and PC, all highly contaminated,while the lowest concentrations are seen at BB, EH, and TK, the cleanest sites. NBhas the highest Pb levels, followed by BC and SH. The lowest concentrations areseen at EH and TK. The highest levels of Zn are seen in BC, followed by NB andPC, and lowest at EH. Cadmium levels are highest at BC and lowest at EH, SH andUB. In the contaminated sites, many metals are elevated. The ER—M is exceededfor all five metals at BC. The ER—M is exceeded for three metals at NB and PC,

Table 1

Metal concentrations measured in the sediments (mg g�1, mean�standard deviation) from the various

Site Hg Cu Pb Zn Cd Total PCBs Total PAHs

BB 0.01�0.005 47.5�6.3* 134 �1.4 189�114* 2.4�0.56* 0.003 0.44

BC 206�7.7** 347 �29.7** 273�9.2** 1693�113** 18.6�0.7** 0.7** 12.8*

EH 0.006�0.002 31.5�0.7 24.5�2.9 66�5.6 1.2�0.14 0 0.08

NB 0.46�0.23* 634�277** 1020�836** 851�308** 5.5�2.3* 0.63** 27.4*

PC 6.3�1.0** 485�46.7** 107�20.8* 525�67.1** 7.1�2.1 0.69** 22.8*

SH 0.02�0.005 113�84* 285�147** 181�79* 1.6�1.3 0.006 0.63

TK 0.19�0.02* 43.8�7.6* 73.2�8.0* 141�13.4 2.1�1.2 0.25** 6.0*

UB 0.03�0.005 112�8.5* 150�12.7* 284�2.8* 1.7�2.4* 0.11* 17.1*

VL 0.36�0.17* 144�37* 221�104** 337�47.4* 3.4�0.1 No data 62**

ER–L 0.15 34 46.7 150 1.2 0.023 4.02

ER–M 0.71 270 218 410 9.6 0.18 44.79

Selected organic contaminants in sediments (mg g�1), taken from EPA data. The ER—L and ER—M

values (Long et al., 1995) for PCB, polychlorinated biphenyls; PAH, polynuclear aromatic hydrocarbons

are included at the bottom of the table for reference. Data with * exceed the ER—L, those with ** exceed

the ER—M.

while the ER—L is exceeded for the other two (NB) or one of the other two metalsmeasured (PC). Pearson correlation coefficients revealed strong correlations amongthe metals. Hg was correlated with Cd (r=0.83, P=0.002), and with Zn (r=0.75,P=0.008); Cu correlated with Pb (r=0.78, P=0.002) and Zn (r=0.68, P=0.002),on the log scale.Data on organics (total PCBs and total PAHs in sediment taken from other

sources) (Adams et al., 1998; Eckenfelder, Inc., 1991) are also shown. The sitesconsidered clean did not exceed ER–L values for these organic contaminants, whileBC, NB, PC, SH, and UB exceed the ER–M for PCBs. This reflects the generalcontamination in the NY/NJ harbor estuary. No site exceeded the ER-M for PAH,but NB, PC and VL had quite high concentrations.

3.2. Larval prey captures

Mean number of captures differed significantly among sites (ANOVA,F8, 438=13.37). On day 3, the lowest mean number caught in 5 min (0.62�1.03) wasby TK larvae (N=60), whereas the highest captures were by larvae from UB(3.06�1.70; N=60), VL (2.77�2.04; N=60), BB (2.53�1.81; N=30), EH(2.40�1.98; N=30), and NB (2.39�1.94; N=30; Fig. 1). The TK larvae capturedsignificantly fewer brine shrimp than those from any other site except SH (N=57).The UB, VL, BB, and EH larvae all caught significantly more than SH larvae. TheUB captures exceeded PC (N=60) and BC (N=50) captures, and VL capturesexceeded PC captures. However, the low capture by TK larvae on day 3 may reflecta slower development time than the northern NJ populations (Weis & Weis 1989b).

Fig. 1. Captures of Artemia nauplii in 5 min by mummichog larvae from each study site: &, 3-day old

larvae; &, 8-day old larvae. See Section 3.2 for statistical analysis.

By day 8 after hatching, all groups caught far more brine shrimp than at day 3,and the sites differed significantly in the mean number of captures (ANOVA,F8, 465=12.82, P<0.0001), with a range from 4.68�0.71(SD) at PC to 2.33�1.67 atBC. Most of the other groups caught an average of >4 nauplii (out of 5 present).Multiple comparisons by Tukey’s method showed that BC’s mean number of cap-tures was significantly smaller than the mean at all other sites except SH, where themean was smaller than the five sites with the highest capture rates. The mean numberof captures at the site with the third lowest capture rate, NB, was significantlysmaller than the mean at PC.

3.3. Relations of contaminants with larval behavior

Concentration of Hg in sediment was negatively correlated with 8-day old larvalcaptures (rG=�0.35). Lead in sediment was also inversely correlated with 8-day oldlarval captures (rG=�0.17) as was Zn (rG=�0.31), Cd (rG=�0.28), and PCBs(rG=�0.13). All of these correlations were statistically significant except for PCBs.The PAHs concentration in sediment was positively correlated with 3-day old larvalcaptures (rG=0.11) but not significantly. These relationships are also shown inTable 2. In general, these statistical correlations were modest and there is a widevariation in the data.

4. Discussion

In general, significant negative correlations were seen for many individual con-taminants in sediments and the prey capture rate of the 8-day old larvae. Since manyof the contaminants co-vary, the responses reflect general overall contaminantloading, rather than responses to individual contaminants. Earlier we found thatadult prey capture behavior showed a good association with general contamination,(Weis, Samson et al., 2001), in that high capture rates were seen in all the cleanest

Table 2

Correlations between behavioral biomarkers and contaminants in sediment; rG=generalized correlation

coefficient for discrete data. Italic data are significant to the 0.05 level

Sediment contaminants Larval captures

rG/P value rG/P value

Age 3 days Age 8 days

Hg 0.03/0.7 �0.35/<0.001

Pb 0.10/0.14 �0.17/0.0055

Cu 0.02/0.83 �0.06/0.34

Zn 0.04/0.60 �0.31/<0.001

Cd �0.03/0.67 �0.28/<0.001

PCBs 0.01/0.95 �0.13/0.032

PAHs 0.15/0.056 0.04/0.52

sites, and poor capture rates were seen in the highly contaminated sites. Sincecontaminants co-varied, it was not possible to relate the behavioral changes to anyspecific contaminant. One contaminant that did not correlate with adult prey cap-ture ability was PAHs. This lack of association of PAHs and impaired behavior wasalso seen in the present study with larvae. However, compared to adult prey capture,larval prey capture behavior appears to be much less useful as a biomarker. It mightbe more sensitive if field-caught larvae were used; these would have developed asembryos in close association with the contaminated sediments and would have beenexposed to the water after hatching.For the 3-day old lab-raised larvae, the lowest rate of prey capture was seen for

TK, one of the most pristine sites, and a high rate was seen at PC, a highly con-taminated site. Captures by 8-day old larvae were somewhat more useful, with thelowest rate being at BC, the most contaminated site. High capture rates were seenfor larvae from BB, TK, and EH, the cleanest sites. However, high capture rateswere also seen in PC larvae. This population has previously been shown to haveembryonic tolerance to some of the contaminants at the site (Weis, Weis, Heber, &Vaidya, 1981), which may partially explain this observation.Adult mummichogs are nektonic and are affected indirectly (primarily via food),

rather than directly, by sediment contaminants, although they can ingest sediments.Larval fish can be exposed to contaminants directly from the water. However, theycan also be affected by contaminants to which they were exposed during embryonicdevelopment (Weis & Weis, 1995a), which can have delayed effects seen afterhatching. They can be affected by contaminants transferred maternally via the yolk.Contaminants in the female’s liver may be put into the yolk as a method ofdepuration, potentially affecting the next generation. High levels of contaminanttransfer and effects on embryos have been shown primarily for organic con-taminants (Binder & Lech, 1984; Smith & Cole, 1973; Walker et al., 1994). Orga-nochlorines, for example, are often found in equal concentrations in eggs as inmaternal tissue (Fisk & Johnson, 1998; Miller, 1993). For metals, however, there isgenerally a lower transfer to eggs, and there is often not a good correlation betweencontaminants in the female’s liver and in her eggs (Johnston, Bodaly, Latif, Fudge,& Strange, 2001; Toppin et al., 1987). Zhou, Weis, and Weis (1998) found that PCand TK mummichog larvae raised in clean water did not differ in Hg content. Incontrast, Hammerschmidt, Wiener, Frazier, and Rada (1999) found that themethylmercury content of eggs from yellow perch from lakes with varying levels ofmercury was strongly correlated with the maternal level. Similarly, Latif, Bodaly,Johnston, and Fudge (2001) found a correlation between maternal and egg Hg inwalleye from contaminated and relatively pristine lakes. Hatching success andembryonic heart rate were correlated with waterborne Hg but not with egg Hg, andlarval deformities were not correlated with Hg either in the eggs or the water. Ana-lysis of liver metals in adult fish from our sites (Weis, Samson et al., 2001) indicatedthat BC adults had average levels of Cu, Pb, and Zn, but, along with PC adults, veryhigh levels of Hg.Behavioral effects of embryonic exposure to methylmercury tended to be transient

if the larvae were subsequently raised in clean water (Weis & Weis, 1995a,b; Zhou et

al., 2001), as in this study. So, one would expect effects of prior exposure to be seenin newly hatched larvae, which have not yet had much time to depurate. However,impairment of prey capture of 3-day old larvae did not correlate well with site con-taminants.Prey capture success as a behavioral biomarker is ecologically relevant, and in

adult mummichogs, correlates well to the overall contamination level and to the fishdiet in the field (Weis, Samson et al., 2001). Unlike larvae, adults have a longer timeto accumulate contaminants in their tissues that could lead to impaired behavior.The larvae in this study were exposed only via maternal transfer, since they wereraised in clean water in the laboratory. Effective prey capture is even more essentialfor larvae than for older mummichogs, since larvae are more carnivorous and mustcapture prey to survive, while older fish eat a more varied diet including algae anddetritus (Kneib & Stiven, 1978). Inadequate nutrition during larval life can result inmortality due to starvation. If larval prey capture were very sensitive to con-taminants, we probably would not have found populations surviving at the pollutedsites. In fact, the one site at which the population appeared to be quite small wasBC, which is the most highly contaminated study site and in which larval prey cap-ture was clearly impaired.For the larvae in this study, behavioral responses (in terms of prey capture ability)

were relatively insensitive to site contamination. For 8-day larvae, the only site thatcould be clearly separated from the others and in which the fish were clearlyimpacted is BC, which is a grossly contaminated Superfund site. It is possible thatresponses to lower concentrations of contaminants might have been seen if we hadcollected the larvae from the field, so that they would have been exposed to thecontaminants during embryonic development, rather than raising them in cleanwater in the laboratory. However, Zhou et al. (2001) raised PC embryos in bothclean water and a simulated PC environment (water and sediments), and found nosignificant difference in larval behavior. It is also possible that other unmeasuredcontaminants might be confounding our results.Leamon, Schultz, and Crivello (2000) evaluated four health indices in mummi-

chogs from five uncontaminated sites, and found great variability in mean values. Itwas not clear what factors were responsible for the variation. They concluded thatsuch health indices in such an inherently variable species may not be useful candi-dates as biomarkers.In summary, we have found that prey capture behavior of larval mummichogs

from previously exposed parents was negatively correlated with many environmentalcontaminants, but was a relatively insensitive biomarker, since it was significantlyimpaired only in fish from the most highly contaminated site.

Acknowledgements

We thank Ted Proctor, Celine Santiago-Bass, and Esther Hager for technicalassistance. This work was supported by a grant from the USGS Division of WaterResources Research, number 1434HQ-96-JR-02686.

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Evaluating prey capture by larval mummichogs (Fundulus heteroclitus) as a potential biomarker for...

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