Cyprinodon Variegatus Research Articles

Body water content over a range of ambient salinities in the sheepshead minnow

Body water content was determined on groups of Cyprinodon variegatus after sequential acclimation to ambient salinities in the range from fresh water to 100%. A multiple linear regression model applied to the data included body mass (M) of individuals and acclimation salinity (S) as independent variables, and body water content (W) as the dependent variable. The model that described the relationship was W(g) = 0·059 + 0·723 M (g)–0001 S (%). Converting values of body water content to percent of wet body mass produced a range of values from 74·5% in fresh water to 72·0% at 100%, only a 2·5% difference in body water content over this wide range of ambient salinities.

An Evaluation of the Aquatic Hazard of Cumene (Isopropyl Benzene)

Cumene manufacturers were required under a TSCA Section 4(a) test rule to evaluate the aquatic toxicity of cumene to daphnids, rainbow trout, mysid shrimp, and sheepshead minnows. Because of cumene′s high volatility (vapor pressure, 3.2 mm Hg at 20°C), all tests were conducted under flowthrough conditions using a proportional diluter system. The 96-hr LC 50s for rainbow trout, sheepshead minnow, and mysid shrimp, based on mean measured concentrations, were 4.8, 4.7, and 1.3 mg/liter, respectively. The 48-hr daphnid EC 50 was 4.0 mg/liter. Although cumene is considered moderately toxic to aquatic organisms under rigorous laboratory conditions, its volatility and biodegradability greatly reduce its hazard to the aquatic environment.

Toxicity characterization of an industrial and a municipal effluent discharging to the marine environment

Toxicity Identification Evaluation (TIE) methods have proven very useful in characterizing, identifying and confirming toxicants in environmental samples. This report describes the characterization of toxicants present in two effluents, industrial and municipal, discharged into the marine environment. A toxicity characterization consists of dividing an effluent sample into several relatively unique chemical fractions. Manipulations used to generate these fractions include aeration, filtration, chelation, oxidant reduction, reverse phase chromatography, and graduated pH adjustments. Marine toxicity tests used include mysids ( Mysidopsis bahia), fish ( Menidia beryllina and Cyprinodon variegatus), macroalga ( Champia parvula) and sea urchins ( Arbacia punctulata). Results of this TIE demonstrated that both effluents contained toxicity predominantly due to metals and organic contaminants. Ammonia toxicity in the municipal effluent was sample dependent. This study illustrates that the use of marine toxicity tests, TIE procedures and historical data can be combined to better understand the nature of toxicity discharged to the marine environment.

The effect of salinity on the acute toxicity of total and free cadmium to a Chesapeake Bay copepod and fish

The objective of this study was to determine the influence of a range of salinities (5, 15 and 25 ppt) on the acute toxicity of total and free cadmium to the sheepshead minnow ( Cyprinodon variegatus) larvae and the copepod Eurytemora affinis nauplii. Data were analysed to determine if the acute toxicity (96 h LC 50) was different among salinities for the test species. Total cadmium was measured in selected test conditions and the proportion of total cadmium as Cd 2+ (free ion or toxic form) was determined at each salinity. Ninety-six hour LC 50 values for C. variegatus were 180.3, 312.4 and 495.5 μg l −1 total cadmium at 5, 15 and 25 ppt, respectively. A significant increase in LC 50 values with salinity was most likely related to a decrease in the free ion as salinity increased. Ninety-six hour LC 50 values for E. affinis were 51.6, 213.2 and 82.9 μg l −1 total cadmium at 5, 15 and 25 ppt, respectively. A comparison of LC 50 values for the copepod between salinities showed a significant difference between 5 and 15 ppt and between 15 and 25 ppt. There was no difference in LC 50 values between 5 and 25 ppt. The physiological characteristics of E. affinis were most likely responsible for the higher tolerance at the middle salinity. Cadmium speciation in the various test salinities was dominated by association with inorganic binding ligands; organic complexation was negligible. The speciation at all salinities was dominated by CdCl + and CdCl 0 2. The free ion accounted for 20, 8 and 4.5% of the total cadmium at 5, 15 and 25 ppt, respectively. These data have important implications for estuaries such as Chesapeake Bay because the presence of the toxic form of cadmium will increase as salinity decreases.

Use of estuarine water column tests for detecting toxic conditions in ambient areas of the chesapeake bay watershed

AbstractVarious estuarine water column toxicity tests were conducted twice in nine different ambient stations in the Chesapeake Bay watershed over a 2‐year period (1991 to 1993) to determine if toxic conditions existed. The following 8‐d toxicity tests were conducted: larval sheepshead minnow (Cyprinodon variegatus) survival and growth test; larval grass shrimp (Palaemonetes pugio) survival and growth test; and a copepod (Eurytemora affinis) life‐cycle test. During the second year of testing, two 48‐h coot clam (Mulinia lateralis) tests were conducted at each station during each testing period. In 1991, the toxicity tests were conducted twice at stations in the Potomac River at Morgantown and Dahlgren, and in the Patapsco River and the Wye River at the Manor House. All of the above tests were conducted during the fall of 1992 and spring of 1993 at two stations in the Wye River, Nanticoke River, and Middle River. Inorganic contaminants, organic contaminants, and water‐quality conditions were measured concurrently during the toxicity testing of ambient water. In 1991, reduced growth of sheepshead minnow larvae was reported at both Potomac River stations during the first test. Significant mortality of either the copepod or sheepshead minnow larvae was also reported at the Wye River during both tests. Results from the 1992/93 testing generally showed minimal effects for three of the test species at all stations. Reduced normal shell development was reported for the coot clam at both Middle River stations during the fall and spring tests concurrently with concentrations of various trace metals that exceeded chronic marine water‐quality criteria.

EFFECTS OF OCTAMETHYLCYCLOTETRASILOXANE (OMCTS) ON FRESHWATER AND MARINE ORGANISMS

The toxicity of octamethylcyclotetrasiloxane (OMCTS) to representative freshwater and marine fish and invertebrates was investigated. Testing procedures followed Toxic Substance Control Act (TSCA) guidelines with chemical-specific adaptations as presented in the OMCTS Testing Consent Order (Docket OPTS-42071A). The physicochemical properties and behavior of OMCTS (i.e., high volatility, low water solubility) precluded the use of conventional experimental practices and exposure systems. Procedures and systems developed during these investigations provided a mechanism that produced exposure levels equal to the maximum achievable (i.e., “functional”) solubility of OMCTS in natural dilution waters. The toxicant delivery systems and exposure chambers were designed to minimize volatilization by elimination of the air/water interface. The flow-through systems maintained consistent exposure concentrations and adhered to U.S. Environmental Protection Agency (EPA) Guideline test performance criteria. The “functional” water solubility of OMCTS in freshwater and seawater ranged from 14 to 30 μg/L and from 6.0 to 9.0 μg/L, respectively. Functional water solubility appeared to vary slightly with test conditions and dilution water characteristics. Continuous exposures of 2 to 93 d were conducted during these investigations with daphnids (Daphnia magna), rainbow trout (Oncorhynchus mykiss), mysids (Mysidopsis bahia), and sheepshead minnow (Cyprinodon variegatus). The rainbow trout was determined to be the most sensitive species to OMCTS (14-d LC50 = 10 μg/L). At levels equal to the functional water solubility, OMCTS was not acutely toxic to D. magna, mysids, or sheepshead minnow. The survival of D. magna was reduced by 16%, relative to the control organisms, after 21-d exposures to 15 μg/L OMCTS; exposure to 7.9 μg/L OMCTS or less had no effect on daphnid survival or reproduction. No toxicity was observed at the highest concentration tested in a 93-d exposure of rainbow trout early life stages. The no-observed-effect concentration for this study was 4.4 μg/L, the same as determined in a 14-d extended acute study.

Individual and interactive effects of salinity and initial fish density on a salt marsh assemblage

We used static outdoor mesocosms (155 1) to study the effects over 60 d of 3 levels of total fish density and 3 levels of salinity (1, 5, and 32 ppt) on growth and survival of juvenile fish (silversides Menidia beryllina, hereafter referred to as Menidia; and sheepshead minnows Cyprinodon variegatus, hereafter Cyprinodon) that are common to salt marsh pools of the eastern United States. Interactions between these 2 species and rainwater killifish Lucania parva (hereafter Lucania) were also examined. There was a general decline in the rate of growth and the percentage survival with increasing fish density. Salinity and density interacted significantly such that the percentage survival of Cyprinodon was lowest in the high salinity-high density treatment compared to most other treatments. It did not appear that Cyprinodon or Menidia interacted strongly with Lucania, since growth and survival of the former 2 species were Independent of abundance of Lucania. Fish simultaneously maintalned in permeable enclosures in the field generally had similar or lower rates of growth than those in mesocosms, indicating that conditions in the mesocosms were not Inherently more stressful than conditions in natural salt marsh pools. It appears that t h ~ s fish assemblage 1s regulated in part by both a biotic (density/competition) and an abiotic factor (salinity). We conclude that, under circumstances in which conditions are severe due to high total fish density, a level of salinity that appears to be otherwise inconsequential may have important lmplicatlons for community structure by lmpactlng survlval of one species.

Myxosporean parasites of the genus Kudoa meglitsch, 1947 from some Gulf of Mexico fishes: Description of two new species and notes on their ultrastructure

Summary Species of the genus Kudoa infecting muscles are described from 7 fish hosts collected in salt and brackish waters along coastal Mississippi in the northern Gulf of Mexico. Two of 5 recorded species are regarded as new species. Kudoa shkae n. sp. from trunk muscles of Arius felis has rather rounded spores, average 7.5 urn in side view, which are formed within large polysporic plasmodia. The plasmodium boundary forms button-shaped projections abutting on intact sarcoplasm. K. leiostomi n. sp. from trunk muscles of Leiostomus xanthurus has spores quadrate in the apical view, averaging 9.1 μm in width; it also forms a large polysporic plasmodium. In spores of both species, the sporoplasm is represented by the cell doublet composed of an enveloped and an enveloping cell. Other unidentified species of Kudoa infected other fishes: one infected Cyprinodon variegatus, Fundulus grandis, and F. chrysotus; one infected Gambusia affinis; and one infected Menidia beryllina.

The fishes of northern and central Veracruz, Mexico

The northern and central part of Veracruz, Mexico, as herein delimited, is inhabited by 121 species of fish, in 83 genera and 47 families. Four species and 3 families are Nearctic, 28 species and 6 families are Neotropical, and 1 species is circumtropical. Ecologically, 8 species and 4 families are primary, 25 species and 6 families are secondary, 30 families are peripheral, and 7 families are marine, many of them marine accidentals. A mountainous area near Punta del Morro almost reaches the sea, and acts as a filter for primary and secondary species. Its importance had not been described in detail. From the north, the following species range to Punta del Morro or less:astyanax mexicanus, Dionda ipni, Ictalurus cf.furcatus, I. cf.punctatus, Lucania parva, Cyprinodon variegatus, Gambusia affinis, G. vittata, Heterandria sp.,Poecilia formosa, P. latipinna, Xiphophorus birchmani, X. variatus, Cichlasoma cyanoguttatum, C. labridens andC. sp.. From the south, the species that approach or reach Punta del Morro are:Astyanax aeneus, Hyphessobrycon compressus, Rhamdia guatemalensis, R. laticauda, Rivulus cf.robustus, Belonesox belizanus, Poeciliopsis gracilis, Xiphophorus andersi, X. maculatus, andOphisternon aenigmaticum. Eight species including one peripheral are present on both sides and constitute short penetrations across the barrier. At least nine species represent introductions, purposeful or accidental.

Influence of Salinity on Atrazine Toxicity to a Chesapeake Bay Copepod (Eurytemora affinis) and Fish (Cyprinodon variegatus)

The objective of this study was to determine the influence of a range of salinities (5%., 15%., and 25%.) on the acute toxicity of atrazine to nauplii of the copepodEurytemora affinis and larvae of the sheepshead minnow,Cyprinodon variegatus. Ninety-six-hour LC50 values for the copepod were 0.5 mg 1−1, 2.6 mg 1−1, and 13.2 mg 1−1 at salimities of 5%., 15%. and 25%. respectively. A comparison of LC50 values between adjacent salinities showed a statistical difference between 15%. and 25%. but not between 5%. and 15%.. Atrazine was more toxic toE. affinis at the lowest salinity. The 96-h LC50s for the sheepshead minnow were 16.2 mg 1−1, 2.3 mg 1−1, and 2.0 mg 1−1 at salinities of 5%., 15%., and 25%., respectively. There was a statistical difference between LC50 values at 5%. and 15%. but not between 15%. and 25%.. In contrast toE. affinis results, atrazine was more toxic toC. variegatus at the highest salinity. The toxicity data from these species suggest that development of estuarine water quality criteria is warranted.

Concerted evolution at the population level: pupfish HindIII satellite DNA sequences.

The canonical monomers (approximately 170 bp) of an abundant (1.9 x 10(6) copies per diploid genome) satellite DNA sequence family in the genome of Cyprinodon variegatus, a "pupfish" that ranges along the Atlantic coast from Cape Cod to central Mexico, are divergent in base sequence in 10 of 12 samples collected from natural populations. The divergence involves substitutions, deletions, and insertions, is marked in scope (mean pairwise sequence similarity = 61.6%; range = 35-95.9%), is largely confined to the 3' half of the monomer, and is not correlated with the distance among collecting sites. Repetitive cloning and direct genomic sequencing experiments failed to detect intrapopulation and intraindividual variation, suggesting high levels of sequence homogeneity within populations. The satellite sequence has therefore undergone "concerted evolution," at the level of the local population. Concerted evolution has previously almost always been discussed in terms of the divergence of species or higher taxa; its intraspecific occurrence apparently has not been reported previously. The generality of the observation is difficult to evaluate, for although satellite DNAs from a large number of organisms have been studied in detail, there appear to be little or no other data on their sequence variation in natural populations. The relationship (if any) between concerted, population level, satellite DNA divergence and the extent of gene flow/genetic isolation among conspecific natural populations remains to be established.

Hepatocellular Neoplasm in a Wild-Caught Sheepshead Minnow (Cyprinodon variegatus) from the Northern Gulf of Mexico

The sheepshead minnow, Cyprinodon variegatus, is a widely distributed small fish species that inhabits estuaries and inshore waters from New England to northern South America. This species has been used extensively in aquatic environmental toxicity and carcinogenicity tests (Couch et al., 1981; Courtney and Couch, 1984). Hepatic neoplasms have been induced in the sheepshead minnow by exposure to several known chemical carcinogens including diethylnitrosamine (Couch and Courtney, 1987), methylazoxymethanolacetate (Hawkins etal., 1985), and dimethylbenz(a)anthracene (Hawkins et al., 1991). Because of its widespread distribution, limited home range, and proven sensitivity tocarcinogens, the sheepshead minnow appears to be a good candidate to serve as an in situ monitor of environmental carcinogens and other toxicants in coastal waters, especially those of the Gulf of Mexico and Caribbean Sea. To establish background information on the histopathological lesions in sheepshead minnows taken from the wild, we collected and examined specimens from an offshore site presumed to be free of chemical contamination. The present report concerns a hepatic neoplastic lesion, diagnosed as a hepatocellular adenoma, found in a wild sheepshead minnow. Neoplasms from wild sheepshead minnows or spontaneous neoplasms from laboratory specimens previously have not been reported.

Acute toxicity of 4‐nitrophenol, 2,4‐dinitrophenol, terbufos and trichlorfon to grass shrimp (Palaemonetes spp.) and sheepshead minnows (Cyprinodon variegatus) as affected by salinity and temperature

AbstractThe toxicities of two industrial chemicals (4‐nitrophenol and 2,4‐dinitrophenol) and two organophosphate insecticides (terbufos and trichlorfon) to juvenile grass shrimp (Palaemonetes spp.) and sheepshead minnows (Cyprinodon variega‐tus) were determined by static, 96‐h toxicity tests in a factorial design with 12 combinations of salinity and temperature (15, 20, 25, 30 ppt × 17, 22, 27°C). Concentrations of the toxicants, including bioconcentration, were determined as appropriate by gas or liquid chromatography and the use of 14C‐labeled compounds. The 96‐h LC50s for 4‐nitrophenol ranged from 12 to 31 mg/L and for 2,4‐dinitrophenol from 13 to 50 mg/L. Toxicity decreased as salinity increased for 4‐nitrophenol and both test organisms. Toxicity decreased as salinity increased for 2,4‐dinitrophenol and sheepshead minnows, but toxicity to grass shrimp increased as salinity increased. Toxicity decreased with increased temperature for grass shrimp exposed to 2,4‐dinitrophenol and sheepshead minnows exposed to 4‐nitrophenol, increased with temperature for sheepshead minnows exposed to 2,4‐dinitrophenol, and no change was observed for grass shrimp exposed to 4‐nitrophenol. Bioconcentration of phenols in both test organisms increased as concentration increased. The 96‐h LC50s for terbufos ranged from 3.4 to 6.6 μg/L and for trichlorfon from 6.3 to 19,300 μg/L. Terbufos and trichlorfon toxicity to grass shrimp and sheepshead minnows increased with increased temperature. BCFs for terbufos were greater in sheepshead minnows than grass shrimp, but were reversed for trichlorfon.

Salinity and temperature effects on chronic toxicity of 2,4‐dinitrophenol and 4‐nitrophenol to sheepshead minnows (Cyprinodon variegatus)

AbstractToxicity tests (28‐d early‐life‐stage) were conducted to determine the effects of nine combinations of salinity (15, 20, 25 ppt) and temperature (22, 27, 32°C) on the toxicity of 2,4‐dinitrophenol (2,4‐DNP) and 4‐nitrophenol (4‐NP) to sheepshead minnows (Cyprinodon variegatus). The highest tested concentration having no observed effect (NOEC) on mortality and growth was derived weekly. The NOECs at test termination indicated that the survival and growth of fish exposed to 2,4‐dinitrophenol were not significantly affected by salinity, temperature, or the salinity temperature interaction. However, 28‐d NOECs of fish surviving from 4‐nitrophenol exposures were significantly affected by temperature, but the highest value exceeded the lowest by only a factor of two. The overall data suggest that variations of salinity and temperature do not change the NOEC; only the exposure time required to attain the same NOEC is altered.

Toxicity of cadmium, hexavalent chromium and copper to marine fish larvae ( Cyprinodon variegatus) and copepods ( Tisbe battagliai)

For comparative purposes, the toxicity of cadmium, hexavalent chromium and copper to marine fish larvae ( Cyprinodon variegatus) and copepods ( Tisbe battagliai) has been evaluated. Toxicity to fish larvae was measured in terms of survival and growth over 7 days, whilst toxicity to copepods was assessed in terms of survival and reproduction after 8 days exposure. For fish larvae, 96 h LC 50 values (based on mean measured concentrations of total metal ion) were 1.23 mg Cd/litre, 31.6 mg Cr 6+/litre and >0.22 mg Cu/litre. Subchronic values (SChVs) for larval fish survival and growth after 7 days were 0.75 mg Cd/litre, 24.0 mg Cr 6+/litre and 0.16 mg Cu/litre. For copepod nauplii and adults, 96 h LC 50 values were as follows: 0.46 mg Cd/litre and 0.34 mg Cd/litre, respectively; 1.60 Cr 6+/litre, and 5.9 mg Cr 6+/litre respectively; and 0.064 mg Cu/litre and 0.088 mg Cu/litre, respectively. SChVs for naupliar survival and adult survival or reproduction after 8 days were 0.024 mg Cd/litre, 0.42 mg Cr 6+/litre and 0.008 mg Cu/litre.

Short-term Persistence and Stability of Barrier Island Fish Assemblages

The semi-permanent pools along the south shore of a Gulf of Mexico barrier island provide a natural setting in which to investigate short-term faunal stability and persistence. All pools were located south of the primary dune line and may be formed when sand bars join with the beach, or when storms fill depressions. The pools offer a physiologically harsh environment, but overall support a fish fauna of 39 species which is dominated numerically by Cyprinodon variegatus, Gambusia holbrooki and Poecilia latipinna. Persistence of the overall fish assemblage was only moderate (0·61) and seasonal stability of the pool assemblages was variable, with five assemblages showing concordance and four non-concordance. Pools with stable assemblages could not be differentiated from those with non-stable assemblages on the basis of physicochemical characteristics. However, pools with greater faunal stability were those colonized by marsh inhabiting species, while pools dominated by colonizers from the nearby surf zone tended to be more variable. Many surf zone species apparently cannot tolerate the physiological demands of the pools and soon go locally extinct. Thus, assemblage stability is largely determined by the vagaries of colonization and the relative age at which a pool is sampled.

Plasma Osmotic Regulation and Routine Metabolism in the Eustis Pupfish, Cyprinodon variegatus hubbsi (Teleostei: Cyprinodontidae)

We assessed the influence of salinity on plasma osmotic regulation and routine metabolism in the freshwater Eustis pupfish Cyprinodon variegatus hubbsi and compared these results to published data for the widely distributed, euryhaline sheepshead minnow C. v. variegatus. The Eustis pupfish was able to tolerate salinities twice that of normal seawater. Plasma osmotic concentration increased with increasing salinity. In freshwater, Eustis pupfish maintained plasma osmotic concentrations lower than sheepshead minnow. However, this pattern reversed with increasing salinity. Routine metabolism did not differ between the Eustis pupfish and sheepshead minnow when the effect of body mass was statistically removed. The Eustis pupfish, although long isolated in fresh waters, has retained the physiological plasticity generally characteristic of the cyprinodontoids.

Energy content and chemical defense of the articulate brachiopod Liothyrella uva (Jackson, 1912) from the Antarctic Peninsula

Energy levels ( x ̄ ± 1 SD) of whole soft body tissues and shells of the antarctic brachiopod Liothyrella uva (Jackson, 1912) were 9.0 ± 1.0 and 1.1 ± 0.4· kJ· g −1 dry wt, respectively. The majority of the energy in the soft body tissues was attributable to NaOH-soluble protein (17.4% dry wt) and in the shell to lipid (2.6% dry wt). An intact individual with a shell length of 3.4 cm and a wet and dry wt of 5.8 and 2.9 g, respectively, contained a total of 9.6 kJ. As dense populations of L. uva occur in the Southern Ocean, this species represents a considerable potential energy resource for predators, including sea stars and fish (ca 10 3kJ·m −2 in some areas). Total crude extracts of whole brachiopod soft tissues caused significant retraction of sensory tube-feet in 6 species of sympatric sea stars. Control assays employing whole crude extracts of the fresh soft tissues of the antarctic limpet Nacella concinna (Strebel, 1908) or seawater alone did not elicit significant sustained tube-foot retraction. Bioactivity was diminished in frozen extracts of brachiopod soft tissues exposed to the sensory tube-feet of the sea star Odontaster validus (Koehler, 1906), but was not diminished in the tube-foot retraction response of the sea star Neosmilaster georgianus (Studer, 1885). Lyophilized brachiopod soft tissues ground into a fine powder and embedded at a concentration of 2% (wt:vol) in agar pellets containing 5% krill caused significant feeding deterrence in an allopatric fish (the sheepshead minnow Cyprinidon variegatus Lacepede 1803). These findings suggest that, similar to temperate zone and tropical brachiopods, body tissues of this antarctic brachiopod are unpalatable to potential predators.

Morphological and Physiological Consequences of Parasites Encysted in the Bulbus Arteriosus of an Estuarine Fish, the Sheepshead Minnow, Cyprinodon variegatus

The contribution of parasites to host population regulation is undefinable without knowledge of parasite effects on individual host performance and survival. Effects are best determined by examining performance of differentially parasitized hosts under the varying environmental conditions that characterize the host's habitat. The sheepshead minnow, Cyprinodon variegatus, an estuarine fish, is heavily parasitized in the bulbus arteriosus by the heterophyid trematode Ascocotyle pachycystis in semi-enclosed shallow bodies of water in northwestern Florida. Laboratory experiments were conducted to examine the morphological and physiological effects of parasitization of these fish. Differentially parasitized fish were compared for differences in ventricle weight and swimming performance. Parasitized fish ventricles were hypertrophied due to mechanical blockage of normal blood flow by metacercariae in the bulbus. Swimming performance generally was reduced by the presence of parasites, which had their most significant negative effect at cold temperatures and low dissolved oxygen levels.

Humic acid effects on uptake of hexachlorobenzene and hexachlorobiphenyl by sheepshead minnows in static sediment/water systems

AbstractThe effect of humic acid on accumulation of hexachlorobenzene (HCB) and hexachlorobiphenyl (HCBP) by sheepshead minnows (Cyprinodon variegatus) from two separate experiments is presented. In the first experiment, static sediment/water exposure chambers were used to determine the effect of dissolved organic carbon (DOC), in the form of terrestrial humic acid (HA), on partitioning of HCB among sediment, water, and sheepshead minnows. Sediments from three geographically different locations were used to test the effect of added HA (0, 3, and 30 mg/L) on accumulation in fish of sediment‐bound HCB. Total organic carbon levels in sediment and water and residues of HCB (14C‐labeled and unlabeled) in sediment, water, and whole‐body tissue were measured. Fish/sediment ratios or accumulation relative to sediment (ARS) indicated that addition of HA did not reduce accumulation of sediment‐bound toxicants. ARS ranged from 7.5 ± 4 without added HA to 9.3 ± 4 with 30 mg/L added HA, but were not statistically different. In a second experiment using HCBP with 0 and 30 mg/L HA and sediment from one location, HCBP concentration in water averaged 0.29 μg/L in non‐HA tanks, and 0.91 μg/L in the HA tanks, but both ARS ratios averaged 5.4. In conclusion, we believe that these tests indicate that HA does not significantly alter bioavailability of toxicants that are in equilibrium with sediment and water.