Fathead Minnow Eggs Research Articles

The Freshwater Oil Spill Remediation Study (FOReSt): 2018 Pilot Study at the Experimental Lakes Area, Canada

ABSTRACT (#667537) Monitored natural recovery (MNR) was assessed as a non-invasive method for limiting residual oil exposure in the aquatic environment following contained spills of Cold Lake Blend diluted bitumen (CLB) and conventional heavy crude (CHV) at the IISD-Experimental Lakes Area in Canada. Oils were applied and left in place for 72h to simulate potential spill cleanup response times. After physical removal of free surface oil, biological response and recovery (microbes, zooplankton communities, emergent insects, and benthic invertebrate) was assessed over 80d and exposure of polycyclic aromatic compounds (PACs) and their alkylated forms (aPACS) in water and sediment were characterized. Embryonic development of fathead minnow eggs exposed to water from each of the enclosures was used to determine potential impacts on fish early life stage development. There were significantly different concentrations of PACs in the enclosures treated with diluted bitumen and CHV immediately after application and attenuation differed between the two products throughout the study period. Water contained primarily 3 ring PACs and aPACs. Microbial taxa with known oil degrading capacity increased in water relative to total community abundance. Emergent insect abundance was significantly lower in both oil treated enclosures relative to reference enclosures, but fish development was not significantly impacted by oil treatments. Monitored natural recovery could be successfully applied to oil spill affected freshwater shorelines, but additional data are required to determine long term recovery trajectories.

Toxicity of dinonylnaphthalene sulfonates to Pimephales promelas and epibenthic invertebrates

Dinonylnaphthalene sulfonic acids (NSAs) are high production volume chemicals that are used primarily as additives in a wide range of industrial products (i.e., coatings, sealants, fuels, metal-extractants, paints, rubber materials). This study examined the effect of three NSA congeners on freshwater organisms: barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS). Chronic effects were characterized by exposing fertilized fathead minnow eggs to sediment-associated NSAs and measuring various developmental and growth endpoints for 21 d. No effects in hatch success and larval growth were observed when fathead minnow eggs were exposed to CaDNS and DNDS concentrations up to 246 and 798 μg/g dry weight, respectively, in spiked sediment (~2% organic carbon). However, when NSAs were associated with substrate containing no organic carbon (sand), EC50s for fathead minnow hatch success, larval growth, biomass production, and overall survival were 58.3, 18.8, 15.5, and 13.8 μg/L, respectively, for CaDNS. Acute effect characterization was also conducted in water-only exposures for the three NSA congeners using the freshwater amphipod Hyalella azteca, the pulmonate snail Planorbella pilsbryi, and larval freshwater mussels Lampsilis cardium and Lampsilis siliquoidea. The sulfonate salts (BaDNS and CaDNS) were significantly more acutely toxic to all tested invertebrates in the water-only exposures, with LC50s ranging from 0.47 to 12.1 μg/L, compared to DNDS (LC50s ≥ 98.2 μg/L). This is the first study to provide empirical data on the aquatic toxicity of three NSA congeners.

Meltwater from snow contaminated by oil sands emissions is toxic to larval fish, but not spring river water

To assess the toxicity of winter-time atmospheric deposition in the oil sands mining area of Northern Alberta, embryo-larval fathead minnow (Pimephales promelas) were exposed to snowmelt samples. Snow was collected in 2011–2014 near (<7km) oil sands open pit mining operations in the Athabasca River watershed and at sites far from (>25km) oil sands mining. Snow was shipped frozen back to the laboratory, melted, and amended with essential ions prior to testing. Fertilized fathead minnow eggs were exposed (<24h post-fertilization to 7–16days post-hatch) to a range of 25%–100% snowmelt. Snow samples far from (25–277km away) surface mining operations and upgrading facilities did not affect larval fathead minnow survival at 100%. Snow samples from sites near surface mining and refining activities (<7km) showed reduced larval minnow survival. There was some variability in the potencies of snow year-to-year from 2011 to 2014, and there were increases in deformities in minnows exposed to snow from 1 site on the Steepbank River. Although exposure to snowmelt from sites near oil sands surface mining operations caused effects in larval fish, spring melt water from these same sites in late March–May of 2010, 2013 and 2014 showed no effects on larval survival when tested at 100%. Snow was analyzed for metals, total naphthenic acid concentrations, parent PAHs and alkylated PAHs. Naphthenic acid concentrations in snow were below those known to affect fish larvae. Concentrations of metals in ion-amended snow were below published water quality guideline concentrations. Compared to other sites, the snowmelt samples collected close to mining and upgrading activities had higher concentrations of PAHs and alkylated PAHs associated with airborne deposition of fugitive dusts from mining and coke piles, and in aerosols and particles from stack emissions. CapsuleSnow collected close to oil sands surface mining sites is toxic to larval fathead minnows in the lab; however spring melt water samples from the same sites do not reduce larval fish survival.

The Relationship between Organic Loading and Effects on Fish Reproduction for Pulp Mill Effluents across Canada.

This study builds upon the work of a multiagency consortium tasked with determining cost-effective solutions for the effects of pulp mill effluents on fish reproduction. A laboratory fathead minnow egg production test and chemical characterization tools were used to benchmark 81 effluents from 20 mills across Canada, representing the major pulping, bleaching, and effluent treatment technologies. For Kraft and mechanical pulp mills, effluents containing less than 20 mg/L BOD5 were found to have the greatest probability of having no effects. Organic loading, expressed as the total detected solvent-extractable components by gas chromatography/mass spectrometry (GC/MS), also correlated with decreased egg laying. Exceptions were found for specific Kraft, mechanical, and sulfite mills, suggesting yet unidentified causative agents are involved. Recycled fiber mill effluents, tested for the first time, were found to have little potential for reproductive effects despite large variations in BOD5 and GC/MS profiles. Effluent treatment systems across all production types were generally efficient, achieving a combined 82-98% BOD5 removal. Further reductions of final effluent organic loadings toward the target of less than 20 mg/L are recommended and can be realized through biotreatment optimization, the reduction of organic losses associated with production upsets and selecting best available technologies that reduce organic loadings to biotreatment.

Predators Reject Yellow Perch Egg Skeins

AbstractDespite the high rate of egg mortality due to predation, few teleost fishes utilize external casings for protecting their eggs. The gelatinous egg matrix, or skein, produced by Yellow Perch Perca flavescens may provide a variety of benefits including deterring egg predators. This study explored the chemical components of the skein in addition to testing the preferences of two common egg predators, Round Goby Neogobius melanostomus and calico crayfish Orconectes immunis, when presented with three potential egg prey: Yellow Perch eggs in the skein, Yellow Perch eggs without the skein, and Fathead Minnow Pimephales promelas eggs. Preliminary analyses showed that the skein may contain a variety of potentially noxious components, including piperideine and the galactose‐specific lectin, nattectin. In preference trials, Yellow Perch eggs in the skein were often approached first; however, both predators preferred Yellow Perch eggs with the skein removed and Fathead Minnow eggs rather than Yellow Perch eggs in the skein. Further experiments demonstrated that crayfish spent less time attempting to consume Yellow Perch eggs in the skein after prior exposure to the skein (day 1: 11.0 min ± 1.3 [mean ± SE]; day 2: 7.6 min ± 1.4), reducing time spent damaging the eggs. These results indicate that the skein may help protect eggs from predation.Received July 18, 2016; accepted October 10, 2016 Published online December 12, 2016

Reproductive effects in fathead minnows (Pimphales promelas) following a 21 d exposure to 17α-ethinylestradiol.

17α-ethinylestradiol (EE2) is a synthetic estrogen that is an active ingredient in oral contraception and hormone replacement therapy. Surveys of wastewater treatment plant effluents and surface waters throughout the world have reported EE2 concentrations in the ng/L range, and these low levels can cause significant reproductive effects in fish. This study tested the effects of three environmentally relevant EE2 concentrations: 0.47, 1.54 and 3.92 ng/L using a 21 d short-term reproductive assay to investigate the effects of EE2 on fathead minnow (Pimephales promelas) reproduction. The two highest EE2 concentrations tested in this study caused significant liver gene expression and induction of vitellogenin plasma protein in male fathead minnows. Exposure to 3.92 ng EE2/L increased the production of plasma vitellogenin in the females. Plasma estradiol concentrations were significantly reduced in females exposed to 1.54 and 3.92 ng EE2/L. All three tested concentrations significantly reduced fathead minnow egg production after a 21 d exposure to EE2. The results of this study indicate that the previously reported no observed adverse effect concentration (NOAEC) for EE2 on fathead minnow egg production (1.0 ng/L) may be too high. Because all three treatments resulted in significantly reduced egg production, the lowest observed adverse effect concentration (LOAEC) for EE2 on fathead minnow egg production is 0.47 ng EE2/L. This research estimates a NOAEC for fathead minnow reproduction at 0.24 ng EE2/L following a 21 d exposure. Additionally, induction of vitellogenin is a sensitive indicator of estrogen exposure but does not appear to be predictive of fathead minnow egg production.

Selecting Optimal Eggs and Embryonic Developmental Stages of Fathead Minnow (Pimephales promelas) for Early Life-Stage Toxicity Tests

Aquaculture research has indicated that fish embryo hatching success and larval survival can sometimes be predicted by embryo characteristics, such as blastomere cleavage patterns. An analogous strategy of individual assessment of spawned eggs could also be used to improve the quality of toxicity tests using early life-stages of fish where control-group survival determines experimental validity. Here we explored whether a simple method of assessing fathead minnow eggs and embryos for abnormalities could predict hatch success, and larval size at hatch, as indicators of embryo larval quality. Embryos were classified according to both their developmental stage and the presence of any abnormalities: uneven blastomere cleavage, atypical embryo size or shape, and the presence of inclusions in the yolk. Clutch size and fertilization rate did not predict embryo larval quality. Fewer abnormalities in embryos with ≤32 cells correlated with longer larvae at hatch. Normal embryos were more likely to hatch successfully than abnormal embryos of the same clutch, but because abnormality rates were generally low, much of the variation in hatch success could not be attributed to visible embryo malformations. Blastomere symmetry may be a useful selection criterion in embryos <3 h postfertilization. Where toxicant exposures early in embryonic development are not required or possible, hatch success could be increased by using older embryos that have survived gastrulation. Purposeful selection of embryos with at least two blastomeres, blastomere symmetry, and few inclusions can improve control survival and improve the quality of any generated (sub)lethality data. In our laboratory, application of the egg-selection criteria significantly improved control group hatch success increasing it from a mean of 84.4 to 94.2%.

Influence of elevated alkalinity and natural organic matter (NOM) on tissue-specific metal accumulation and reproductive performance in fathead minnows during chronic, multi-trophic exposures to a metal mine effluent

Metal bioavailability in aquatic organisms is known to be influenced by various water chemistry parameters. The present study examined the influence of alkalinity and natural organic matter (NOM) on tissue-specific metal accumulation and reproductive performance of fathead minnows (Pimephales promelas) during environmentally relevant chronic exposures to a metal mine effluent (MME). Sodium bicarbonate (NaHCO3) or NOM (as commercial humic acid) were added to a Canadian MME [45 percent process water effluent (PWE)] in order to evaluate whether increases in alkalinity (3–4 fold) or NOM (~1.5–3mg/L dissolved organic carbon) would reduce metal accumulation and mitigate reproductive toxicity in fathead minnows during a 21-day multi-trophic exposure. Eleven metals (barium, boron, cobalt, copper, lithium, manganese, molybdenum, nickel, rubidium, selenium, and strontium) were elevated in the 45 percent PWE relative to the reference water. Exposure to the unmodified 45 percent PWE resulted in a decrease of fathead minnow egg production (~300 fewer eggs/pair) relative to the unmodified reference water, over the 21-day exposure period. Water chemistry modifications produced a modest decrease in free ion activity of some metals (as shown by MINTEQ, Version 3) in the 45 percent PWE exposure water, but did not alter the metal burden in the treatment-matched larval Chironomus dilutus (the food source of fish during exposure). The tissue-specific metal accumulation increased in fish exposed to the 45 percent PWE relative to the reference water, irrespective of water chemistry modifications, and the tissue metal concentrations were found to be similar between fish in the unmodified and modified 45 percent PWE (higher alkalinity or NOM) treatments. Interestingly however, increased alkalinity and NOM markedly improved fish egg production both in the reference water (~500 and ~590 additional eggs/pair, respectively) and 45 percent PWE treatments (~570 and ~260 additional eggs/pair, respectively), although fecundity over 21 day exposure consistently remained lower in the 45 percent PWE treatment groups relative to the treatment-matched reference groups. Collectively, these findings suggest that metal accumulation caused by chronic 45 percent PWE exposure cannot solely explain the reproductive toxicity in fish, and decrease in food availability (decrease in C. dilutus abundance in 45 percent PWE exposures) might have played a role. In addition, it appears that NaHCO3 or humic acid mitigated reproductive toxicity in fish exposed to 45 percent PWE by their direct beneficial effects on the physiological status of fish.

Fathead minnow (Pimephales promelas) embryo to adult exposure to decamethylcyclopentasiloxane (D5)

The cyclic siloxane decamethylcyclopentasiloxane (D5) is a high production volume chemical which has recently been assessed under the Canadian Chemicals Management Plan (CMP). Cyclic volatile methyl siloxanes (cVMS) are one of the challenge substances in the CMP batches. To provide toxicity and growth information on a species of relevance to the Canadian environment, we assessed D5 in a fathead minnow (Pimephales promelas) embryo to young adult assay. The test was 65d in length, and exposed fathead minnow eggs to juveniles until near maturity (60d post-hatch). The D5 concentrations in flow-through fish exposure aquaria were about one-third of nominal D5 concentrations. Fathead minnows were exposed to 0.25, 0.82, 1.7, 3.6, and 8.7μgL−1 D5. During the exposure of fathead minnows to D5 there were few effects seen. Egg hatching and larval fish survival and growth were normal. Juvenile fish survival and growth were good in all environmentally-relevant concentrations of D5, and were similar to control fish. The two highest D5 concentrations (8.7μgL−1 and 3.6μgL−1, mean measured D5) increased the condition factors of fathead minnows compared to water control and DMSO control fish. Although there were few effects of D5 in our fathead minnow study, the compound was taken up and stored in fish bodies over the 65-d exposure. The bioconcentration factor for D5 in fathead minnows was 4450, for the lowest environmentally-relevant D5 exposure water concentrations, and 4920 for all D5 exposure concentrations tested.

Effect of Spawning Substrate Area to Male Ratio on Fathead Minnow Egg Production

AbstractA commercially feasible indoor hatching system for fathead minnow Pimephales promelas requires an efficient egg collection process that maximizes egg numbers while minimizing spawning substrate. Four ratios of substrate area to the number of male fathead minnow were compared by stocking approximately 40 males and 80 females into each of sixteen 3.3‐m2 outdoor pools to determine the volume of eggs that could be collected every 2–3 d. No differences in mean egg volume were found among the three lowest ratios of substrate area to the number of males (85, 170, and 255 cm2), and egg volume did not differ between the lowest (85 cm2) and highest (340 cm2) ratios, indicating that 85 cm2 of spawning substrate per male was sufficient. On average, less than one‐third of the males were nesting at any one time. These results strongly suggest that lower spawning substrate area : male ratios should be tested to further refine this new hatchery method.

Effects of progesterone on reproduction and embryonic development in the fathead minnow (Pimephales promelas)

High concentrations (375 ng/L) of the steroid hormone progesterone (P4) were measured in snowmelt runoff associated with large livestock-feeding operations in Wisconsin. To gain insight into the potential endocrine-disrupting effects of P4 in fish, experiments were conducted to evaluate the effects of short-term exposure to environmentally relevant concentrations of P4 on reproduction and embryonic development in the fathead minnow (Pimephales promelas). For the reproduction assay, groups of reproductively mature fish were exposed for 21 d to nominal concentrations of 0, 10, 100, and 1,000 ng/L P4 in a flow-through system, and various key reproductive endpoints (e.g., egg number, fertilization success) were quantified throughout the exposure period. The embryonic development assay consisted of incubating fathead minnow eggs in static culture to quantify the effects of P4 on early development and hatching success. Progesterone caused dose-dependent decreases in fecundity and fertility and significantly reduced gonadosomatic index and vitellogenin gene expression in females. There were no effects of P4 on early embryonic development or hatching success. Progesterone may be a significant endocrine-disrupting chemical in fish.

Life-Cycle Exposure of Fathead Minnows to a Mixture of Six Common Pharmaceuticals and Triclosan

Fathead minnows were exposed for a life cycle to environmentally relevant concentrations of a mixture of six common pharmaceuticals and one personal care product (nominal concentrations: 1,000, 300, 100, 30, or 10 ng/L). Mean measured concentrations of each chemical in the highest fish exposure aquaria were: naproxen 793 ng/L, gemfibrozil 662 ng/L, diclofenac 331 ng/L, ibuprophen 217 ng/L, triclosan 115 ng/L, salicylic acid 67 ng/L, and acetaminophen (chemical analysis inconclusive, nominal 1000 ng/L). Fish exposed for a life cycle even to the highest concentrations of the six pharmaceuticals and personal care product (PPCP) mixture showed no significant changes in growth and development compared to control. Length, weights, condition factors, liver weights, and gonad weights of PPCP-exposed fish were similar to water and solvent controls (0.000005% ethanol v/v). There were no marked effects of PPCP mixture exposure on external sex characteristics of the fish or on egg production. The only parameter that appeared to be affected was percent larval deformities in F1, which showed a significant increase in the 100- and 300-ng/L (nominal) PPCP mixture. Larvae from control fish had 4.7% (water controls) and 3.4% (solvent controls) deformities, compared to 9.3% in the 100-ng/L (nominal) PPCP mixture and 9.2% deformities in the 300-ng/L (nominal) PPCP mixture. Chronic exposure to environmentally relevant concentrations of seven PPCP most often detected in Canadian municipal wastewater effluents (MWWE) did not appear to affect fathead minnow survival, growth, or egg production, although it produced quantitative increases in deformities in the F1 generation.

Effects of water hardness on skeletal development and growth in juvenile fathead minnows

Skeletal growth in vertebrates is partially controlled by the availability of minerals. The correlation between aqueous calcium content and fish skeletal growth (“ossification”) is especially important as calcium absorption from water is an essential route to acquire this mineral. In this study, we test the hypothesis that a calcium-abundant aquatic environment will expedite larval skeletal development in fathead minnows beyond the skeletal development in a low-calcium environment. Fathead minnows were chosen for this study as they are a widely used toxicological model organism with well established rearing protocols. We divided three batches each of fathead minnow eggs from a colony supplied with calcium-abundant water (Ca = 65 ± 1.5 mg/L as CaCO 3; hardness > 175 mg/L) and one with a low, yet adequate calcium content (Ca = 15 ± 0.11 mg/L as CaCO 3; hardness < 50 mg/L) to rear fish. Half of each egg batch was exchanged between laboratories and fish were then reared to 60 days post-hatch under similar conditions. At 60 days, juveniles were sacrificed, cleared and stained. Ossification patterns for cranial (jaw) and caudal (fin) structures were quantified using NIH Image ( http://rsb.info.nih.gov/nih-image/). Fish reared in calcium-abundant water had significantly increased survival but lower whole body mass when compared to their conspecifics in low-calcium water. Cranial ossification patterns did not vary. Caudal fin ossification was statistically significant, but slightly and surprisingly enhanced in juveniles reared in low-calcium water. All observed differences were independent of the origin of fish and imply differences in fish growth among cultures maintained under similar rearing conditions for the purpose of this study. Results of this investigation have implications for the rearing of model organisms for toxicological studies and need to be amended by physiological explorations.

Oxygen Flux As an Indicator of Physiological Stress in Fathead Minnow (Pimephales promelas) Embryos: A Real-Time Biomonitoring System of Water Quality

The detection of harmful chemicals and biological agents in real time is a critical need for protecting freshwater ecosystems. We studied the real-time effects of five environmental contaminants with differing modes of action (atrazine, cadmium chloride, pentachlorophenol, malathion, and potassium cyanide) on respiratory oxygen consumption in 2-day postfertilization fathead minnow (Pimephales promelas) eggs. Our objective was to assess the sensitivity of fathead minnow eggs using the self-referencing micro-optrode technique to detect instantaneous changes in oxygen consumption after brief exposures to low concentrations of contaminants. Oxygen consumption data indicated that the technique is indeed sensitive enough to reliably detect physiological alterations induced by four of the five contaminants. After 2 h of exposure, we identified significant increases in oxygen consumption upon exposure to pentachlorophenol (100 and 1000 microg/L), cadmium chloride (0.0002 and 0.002 microg/L), and atrazine (150 microg/L). In contrast, we observed a significant decrease in oxygen flux after exposuresto potassium cyanide (44 and 66 microg/L) and atrazine (1500 microg/L). No effects were detected after exposures to malathion (200 and 340 microg/L). Our work is the first step in development of a new technique for physiologically coupled biomonitoring as a sensitive and reliable tool for the detection of environmental toxicants.

Life-cycle exposure of fathead minnows (Pimephales promelas) to an ethinylestradiol concentration below 1 ng/L reduces egg fertilization success and demasculinizes males

Forty-eight hours after fertilization, fathead minnow (Pimephales promelas) eggs were exposed to the synthetic estrogen 17alpha-ethinylestradiol (EE2) at nominal concentrations of 0.32 and 0.96 ng/L and measured concentrations of 3.5, 9.6, and 23 ng/L. The fish were observed through the larval, juvenile, and adult stages. Growth, secondary sex characteristics, the liver somatic index, the gonadosomatic index, and fecundity were examined after several lengths of exposure. No significant changes were seen in fry or juvenile growth from 8 to 30 days posthatch (dph). An increase in the ovipositor index (a female secondary sex characteristic) was the most sensitive early response at 60 dph and was seen in fish exposed to EE2 concentrations > or = 3.5 ng/L. Continuation of the EE2 exposure until 150 dph, through maturation and reproduction, allowed measurement of two sensitive end points: decreased egg fertilization and sex ratio (skewed toward females), both of which were significantly affected at the lowest EE2 concentration tested, 0.32 ng/L. The next most sensitive end point was demasculinization (decreased male secondary sex characteristic index) of males exposed to an EE2 concentration of 0.96 ng/L. The effects of low concentrations of EE2 (0.32 and 0.96 ng/L) were manifested in male fish (decreased male sex characteristics and reduced egg fertilization success), whereas female fish showed no changes in the gonadosomatic index. Exposure to higher EE2 concentrations negatively affected females, as shown by a reduced gonadosomatic index at 150 dph in fish exposed to > or =3.5 ng/L EE2. Although there were some end points that showed changes at 60 dph, the reproductive end points and external sex characteristics measured in mature fish at 150 dph were more sensitive, with response thresholds of EE2 ranging from 0.32 to 0.96 ng/L. The concentrations of EE2 that negatively affected fathead minnows were similar to or lower than those detected in many municipal wastewater effluents. In conclusion, life-cycle exposure of fathead minnows proved to be a very sensitive bioassay, and responses were seen at concentrations of less than 1 ng/L, which are environmentally relevant concentrations of EE2.

The effects of crayfish predation on phenotypic and life-history variation in fathead minnows

Ecological theory predicts that the timing of the transition between life-history stages should vary with the costs and benefits associated with each stage. For example, the timing of hatching or metamorphosis may vary with the predation risk in each stage. Predator-induced changes in hatching time are well documented in some taxa but have not been reported in fishes. We provide the first empirical evidence that a species of fish can alter its hatching time in response to predator cues. We showed that fathead minnows, Pimephales promelas Rafinesque, 1820, exposed to chemical cues from virile crayfish, Orconectes virilis (Hagen, 1870), foraging on minnow embryos hatch sooner than those exposed to a blank control. Moreover, in the presence of cues from virile crayfish feeding on minnow embryos, the hatchlings exhibited a change in morphology because they had significantly shorter total lengths. There was a significant positive correlation between hatchling size and length of the developmental period, except in the high predation threat treatment. By hatching earlier, the fathead minnows escaped predation from virile crayfish that were actively foraging on fathead minnow eggs. Hatching at a smaller size, however, may make the fry more vulnerable to other predators.

Collection, Removal, and Quantification of Eggs Produced by Rosy Red Fathead Minnows in Outdoor Pools

AbstractEggs produced by rosy red fathead minnows Pimephales promelas held at four densities in 12 outdoor pools were collected and removed from substrate and had their numbers estimated. Adult fish were stocked at a sex ratio of 4:1 (females: males) and at densities of 5.1, 15.3, 25.4, or 35.6 fish/m2. Sodium sulfite (1.5–2.0%) was used to detach fathead minnow eggs from the spawning substrate. Egg numbers were estimated volumetrically based on an average (±SD) of 578 ± 34 eggs per milliliter. Mean daily egg numbers generally increased with fish density, and production ranged from 2,587 ± 2,999 to 9,595 ± 2,423 eggs/kg of broodfish. Averaging all treatments together for the 16‐d period, over 6,000 eggs/d were collected per kilogram of broodfish. Based on this estimate, 500 kg of broodfish in a 1‐ha pond would produce an average of 3 million eggs each day. Assuming an 80% hatching rate, this number of eggs would result in enough fry to stock a 0.5–1.0‐ha pond. The results imply that an intensive production method consisting of harvesting eggs from ponds, indoor hatching, and subsequent fry stocking (as is now practiced for other baitfish species) could be feasible for fathead minnows.

Fathead Minnow Lifecycle Tests for Detection of Endocrine-Disrupting Substances in Effluents

Abstract The goal of this study was to assess the responses of fathead minnows (FHM) exposed to known endocrine-disrupting substances (EDS) in our labs. As well, we wanted to examine the applicability and sensitivity of the full lifecycle FHM test for use on-site, exposing fish to a complex environmentally relevant Canadian effluent. Fathead minnows exposed from the egg stage to ethinylestradiol (EE2, 0-32 ng/L) or methyltestosterone (MT, 0-3200 ng/L) had decreased growth (length, weight) at high concentrations. Development of secondary sex characteristics was a sensitive indicator of exposure to androgen and estrogen. Fish exposed to MT showed premature male sex characteristics such as nuptial tubercles by 30 days post-hatch (dph). These changes were more dramatic in older fish (at 60 and 90 dph), which showed premature male sex characteristics at very low MT concentrations (100 ng/L). Fish exposed to 3.2 ng/L EE2 had premature development of ovipositors at 60 dph. As well, exposure to very high MT concentrations (1000 and 3200 ng/L) caused development of ovipositors after 60 days (but not at 20 and 30 dph), presumably due to aromatization of MT to methylestradiol (as suggested by other researchers). The fathead minnow lifecycle assay, tested with a known estrogen and androgen, proved to be useful for detection of EDS-related changes caused by a real-life effluent mixture. Lifecycle exposures of fathead minnow eggs to bleached sulphite mill effluent (BSME) showed changes in secondary sex characteristics and growth. In contrast to EE2 and MT, fish exposed to BSME had increased growth. Changes in secondary sex characteristics of fish were seen in both male and female minnows exposed to BSME, but there was an overall shift towards increasing numbers of female fish (based on external sex). The full lifecycle assay provides a definitive test for reproductive/EDS effects, and it appears that some of the most sensitive endpoints we studied were the premature development of secondary sex characteristics.

An inexpensive fathead minnow egg incubation and toxicant exposure system

AbstractWe report on an inexpensive, easily constructed system for hatching fathead minnow eggs and maintaining hatched larvae for growth and survivorship studies. Data are presented to illustrate the use of the system for toxicant exposures. This system has applications for both field and laboratory studies.

AN INEXPENSIVE FATHEAD MINNOW EGG INCUBATION AND TOXICANT EXPOSURE SYSTEM

AN INEXPENSIVE FATHEAD MINNOW EGG INCUBATION AND TOXICANT EXPOSURE SYSTEM