Fathead Minnow Larval Survival Research Articles

Effects of low, subchronic exposure of 2,4-Dichlorophenoxyacetic acid (2,4-D) and commercial 2,4-D formulations on early life stages of fathead minnows (Pimephales promelas).

Aquatic herbicides are commonly used to control a wide variety of algae and plants, but they also have the potential to contaminate and affect nontarget organisms. However, the impacts of low-level 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide exposure on larval fish are not well understood. We conducted a series of experiments to determine the effects of low concentrations (0.05, 0.50, and 2.00 ppm) of 2 commercial 2,4-D amine salt herbicide formulations (Weedestroy® AM40 [WAM40] and DMA® 4 IVM [DMA4]) and pure 2,4-D on the development and survival of fathead minnows (Pimephales promelas) at various life cycle stages. Larval survival (30 d post hatch [dph]) was decreased following exposure of eggs and larvae to pure 2,4-D (0.50 ppm; p ≤ 0.001), as well as to WAM40 (0.50 and 2.00 ppm; p ≤ 0.001, p ≤ 0.001) and DMA4 (0.50 and 2.00 ppm; p ≤ 0.001, p ≤ 0.001). The results also narrowed the critical window of exposure for effects on survival to the period between fertilization and 14 dph. Development was not negatively altered by any of the compounds tested, although the commercial formulations increased larval total length and mass at 2.00 ppm. Altogether, the results indicate that the use of 2,4-D herbicides for weed control in aquatic ecosystems at current recommended concentrations (<2 ppm whole lake; <4 ppm spot treatment) could present risks to fathead minnow larval survival. Environ Toxicol Chem 2018;37:2550-2559. © 2018 SETAC.

Mode of sexual differentiation and its influence on the relative sensitivity of the fathead minnow and zebrafish in the fish sexual development test

Exogenous treatment of fish with natural sex hormones and their mimics has been shown to influence gonadal differentiation resulting in biased phenotypic sex-ratios. This has lead to the development of the Fish Sexual Development Test (FSDT) as a method for the detection of endocrine active chemicals. Proposed test organisms include the medaka, zebrafish (ZF) and stickleback, although the guideline also allows for inclusion of species such as the fathead minnow (FHM), provided the test duration allows for sufficient sexual differentiation. However, although the processes underlying sexual differentiation are known to differ for each of these species, it is not known how, or if, these differences would influence the results of the FSDT. In the experiments reported here, responses of the ZF and FHM to prochloraz, a sterol biosynthesis inhibitor and androgen antagonist, were characterized and compared. Exposure to 320 μg/L of prochloraz, from embryo until 60 (ZF) or 95–125 (FHM) days post hatch inhibited somatic growth of both species, but while a negative impact on ZF larval survival was observed (LOEC 32 μg/L) there was no evidence for an effect on FHM larval survival. Prochloraz influenced sexual differentiation in both species by decreasing the proportion of females (LOEC 100 μg/L (ZF), 320 μg/L (FHM)) and delaying completion of sexual differentiation; manifest as an increased incidence of ovotestis in the ZF (LOEC 100 μg/L) and as an increased number of fish with undifferentiated gonads in the FHM (LOEC 320 μg/L). However, while exposure to 320 μg/L prochloraz delayed maturation of the differentiated FHM testis, there was no such effect in the ZF. These results demonstrate that the different strategy of sexual differentiation in the ZF and FHM influences the profile of responses of their gonads to the masculinising effects of prochloraz, but does not affect their overall sensitivity.

A simplified procedure for conducting small scale short‐term embryo toxicity tests with salmonids

A method for conducting short-term (7 day) embryo toxicity tests with rainbow trout is described. The test uses an easily recognizable endpoint that incorporates fertilization success, embryo mortality, and morphogenesis. Method validation included 26 tests on pulp and paper mill effluents and 10 tests with the reference toxicant sodium dodecyl sulphate. The results demonstrate that the method is sensitive and reproducible. Sensitivity, as measured by the minimum statistically significant response, averaged 15.5% of the control performance. Control embryo viability averaged 90% over 36 tests, indicating that the test procedures are robust with low probability of failure. Reference toxicant test results suggested that the short-term embryo toxicity tests were appreciably more sensitive than 96 h acute tests with juvenile rainbow trout and 7 day fathead minnow larval survival and growth tests. This test offers the potential for conducting routine toxicity tests where cold water salmonids are the species of interest and it is desirable to use a more sensitive measure of effects than a 96 h LC50 acute toxicity test with juvenile fish. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 301–307, 1999

A simplified procedure for conducting small scale short-term embryo toxicity tests with salmonids

A method for conducting short-term (7 day) embryo toxicity tests with rainbow trout is described. The test uses an easily recognizable endpoint that incorporates fertilization success, embryo mortality, and morphogenesis. Method validation included 26 tests on pulp and paper mill effluents and 10 tests with the reference toxicant sodium dodecyl sulphate. The results demonstrate that the method is sensitive and reproducible. Sensitivity, as measured by the minimum statistically significant response, averaged 15.5% of the control performance. Control embryo viability averaged 90% over 36 tests, indicating that the test procedures are robust with low probability of failure. Reference toxicant test results suggested that the short-term embryo toxicity tests were appreciably more sensitive than 96 h acute tests with juvenile rainbow trout and 7 day fathead minnow larval survival and growth tests. This test offers the potential for conducting routine toxicity tests where cold water salmonids are the species of interest and it is desirable to use a more sensitive measure of effects than a 96 h LC50 acute toxicity test with juvenile fish. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 301–307, 1999

Effects of organism allocation on toxicity test results

AbstractThe purpose of this study was to investigate the effect of nonrandom allocation of organisms to treatments in aquatic toxicity tests on lethal concentration estimates. Random allocation of organisms is prescribed to avoid the introduction of systematic bias in these tests; however, completely random assignment is usually impractical. A source of systematic bias in a nonrandom allocation scheme is the potential inverse relationship between organism hardiness and the order in which organisms are captured for assigning to treatment (i.e., less hardy and hence more sensitive individuals are captured first). A Monte Carlo simulation experiment was performed to examine such an inverse relationship for a variety of random allocation schemes, focusing on the mortality endpoint in the fathead minnow larval survival and growth toxicity test. Results of the computer simulation experiment indicated that nonrandom allocation of organisms can produce significant bias in estimates of lethal concentration values. Any attempt at randomization resulted in approximately unbiased estimates of lethal concentration values; however, variance of the estimates increased as allocation schemes deviated from the completely random allocation. This study illustrates the importance of proper training of laboratory personnel to implement some form of random organism allocation. Furthermore, many partial random allocation schemes (i.e., those allocating more than one organism at a time) may still yield unbiased estimates of potency endpoints.

EFFECTS OF ORGANISM ALLOCATION ON TOXICITY TEST RESULTS

The purpose of this study was to investigate the effect of nonrandom allocation of organisms to treatments in aquatic toxicity tests on lethal concentration estimates. Random allocation of organisms is prescribed to avoid the introduction of systematic bias in these tests; however, completely random assignment is usually impractical. A source of systematic bias in a nonrandom allocation scheme is the potential inverse relationship between organism hardiness and the order in which organisms are captured for assigning to treatment (i.e., less hardy and hence more sensitive individuals are captured first). A Monte Carlo simulation experiment was performed to examine such an inverse relationship for a variety of random allocation schemes, focusing on the mortality endpoint in the fathead minnow larval survival and growth toxicity test. Results of the computer simulation experiment indicated that nonrandom allocation of organisms can produce significant bias in estimates of lethal concentration values. Any attempt at randomization resulted in approximately unbiased estimates of lethal concentration values; however, variance of the estimates increased as allocation schemes deviated from the completely random allocation. This study illustrates the importance of proper training of laboratory personnel to implement some form of random organism allocation. Furthermore, many partial random allocation schemes (i.e., those allocating more than one organism at a time) may still yield unbiased estimates of potency endpoints.

Review of Whole-Organism Bioassays: Soil, Freshwater Sediment, and Freshwater Assessment in Canada

Whole organism bioassays for the assessment of soil, freshwater sediment, and freshwater quality were evaluated for their application in the assessment and remediation of contaminated sites in Canada under the National Contaminated Sites Remediation Program. Using 3 essential and 12 desirable methodological criteria, bioassays were categorized as currently usable, prototype, or under development. Based on further considerations related to bioassay application, a battery of usable screening and definitive tests was recommended (with suggestions for augmentation) for each medium. Of the 18 bioassays reviewed for soil quality assessment, 6 were usable, 5 were prototypes, and 7 were under development. Battery screening and definitive tests included 14-day Eisenia andrei survival, 120-hr lettuce and radish seedling emergence, and 72-hr Selenastrum capricornutum growth inhibition. Augmentation with the following bioassays was recommended: soil/freshwater bacterial growth, arthropod reproduction, earthworm reproduction, and reproduction of other soil-dependent organisms. Of the 9 bioassays reviewed for freshwater sediment quality assessment, 1 was usable, 2 were prototypes, and 6 were under development. Three bioassays in the latter two groups were considered usable with the imminent completion of research underway. Screening tests selected included 10-day Chironomus tentans survival, 10-day Hyalella Aztec survival, 10-day Hexagenia spp. survival, and 72-hr S. capricornutum growth inhibition. Definitive tests included screening tests, substituting 28-day H. azteca sexual maturation for 10-day survival. Augmentation with the following bioassays was recommended: sediment/freshwater bacterial test, 28-day Tubifex tubifex reproduction, and rooted aquatic plant growth. Of the 25 bioassays considered for freshwater quality assessment, 8 were usable, 7 were prototypes, and 10 were under development. Screening tests selected included 72-hr S. capricornutum growth inhibition; 48-hr Daphnia sp. survival, and 5- and 15-min Photobacterium phosphoreum bioluminescence. Definitive tests included first screening test, 7-day Ceriodaphnia dubia, 7-day fathead minnow larval survival, or 96-hr rainbow trout survival. Augmentation with the following bioassays was recommended: Brachionus calyciflorus 24-hr survival, 48-hr reproduction; freshwater bacterial growth; and aquatic vascular plant growth.

Variability in the performance of the seven-day fathead minnow (pimephales promelas) larval survival and growth test: An intra- and interlaboratory study

The U.S. Environmental Protection Agency (EPA) has developed a “Seven-Day Fathead Minnow Larval Survival and Growth Test” for measuring the toxicity of effluents. This study evaluated the ease and performance and the intra- and interlaboratory variability of this 7-d test using two reference toxicants (sodium pentachlorophenate and potassium dichromate), two refinery effluents, and one low-volume internal waste stream from an electric power plant. Ten different laboratories representing academia, private industry, contractors, the state EPA, and the U.S. EPA participated in this study. The reference toxicants were tested twice during two separate test periods, and each effluent and waste stream was tested once. Using EPA's criteria for a successful test, 90% of the 140 planned tests were completed as valid tests. The intralaboratory variability of the survival (LC50) and growth (IC50) results for tests conducted concurrently (spatial variability), expressed as the coefficient of variation (C.V.), ranged between 5.9 and 15.6% and between 9.1 and 26.1%, respectively. The intralaboratory variability of the survival (LC50) and growth (IC50) results for tests conducted at two different times (temporal variability), expressed as C.V., ranged between 14.5 and 25.3% and between 17.6 and 22.7%, respectively. The interlaboratory variability of the survival (LC50) and growth (IC50) results, expressed as C.V., ranged between 24.1 and 43.7% and between 22.4 and 88.0%, respectively. Overall, the variability of the 7-d fathead minnow test was similar to the variability observed with other toxicity tests and with analytical chemistry measurements of environmental samples.

Evaluation and comparison of two short-term fathead minnow tests for estimating chronic toxicity

The purpose of this study was to evaluate and compare the fathead minnow larval survival and growth test (larval test) and the fathead minnow embryo-larval survival and teratogenicity test (embryo-larval test). These tests were developed for use by the U.S. Environmental Protection Agency regional and state programs and the National Pollutant Discharge Elimination System permittees to estimate the chronic toxicity of effluents and receiving waters. Five larval tests with the reference toxicant, sodium pentachlorophenate, gave a mean subchronic value of 253 μg 1 −1 with a relative standard deviation of 39%. The mean LC 50, LC 10 and LC 1 values and their relative standard deviation for the embryo-larval test were 313 ± 6.4%, 224 ± 18% and 172 ± 27% μg 1 −1, respectively. The mean subchronic value for six larval tests with the reference toxicant, sodium dodecylsulfate was 6.0 mg 1 −1 with a relative standard deviation of 23%. The mean LC 50, LC 10 and LC 1 values for the embryo-larval test were 5.8 ± 2.6% 4.2 ± 5.9% and 3.3 ± 9.4% mg −1, respectively. Both types of test methods had a high-low ratio of no observable effect concentration values of 2, the reciprocal of the dilution factor. The mean subchronic value for four larval tests with linear alkylbenzene sulfonate was 2.1 mg 1 −1 and the subchronic values ranged from 1.7 to 3.4 mg 1 −1. Side-by-side tests were conducted with three effluents and hexavalent chromium. The larval test was more sensitive to two of the effluents and hexavalent chromium. The low test concentration of the third effluent caused an adverse effect in both tests.