Thyroid axis disruption in juvenile brown trout (Salmo trutta) exposed to the flame retardant β-tetrabromoethylcyclohexane (β-TBECH) via the diet

Tetrabromoethylcyclohexane (TBECH) is an additive brominated flame retardant used in domestic and industrial applications. It has been detected in wildlife, and there is early evidence that it is an endocrine disruptor. Whereas other brominated flame retardants with similar physicochemical properties have been shown to disrupt the thyroid axis, no such evaluation has been conducted for TBECH. To elucidate this, juvenile brown trout (Salmo trutta) were fed either a control diet or diets containing low, medium, or high doses of β-TBECH, the isomer most frequently detected in wildlife, for 56 days (uptake phase) followed by a control diet for an additional 77 days (depuration phase). Eight fish per treatment were lethally sampled on uptake days 7, 14, 21, 35, 49, and 56 and on depuration days 7, 21, 35, 49, and 77 to assess fish condition, circulating free and total triiodothyronine and thyroxine, and thyroid epithelial cell height. Although there was no effect on condition factor, there was a significant reduction in total plasma thyroxine in the high dose group and a significant increase in mean thyroid epithelial cell height in the low, medium, and high dose groups during the uptake phase, whereas there were no differences in the depuration phase. These results indicate that β-TBECH may modulate the thyroid axis in fish at environmentally relevant concentrations.     

Repeated use of oil for frying fish. Effects of feeding the fried fish to rats

Four groups of weanling male albino rats (Wistar strain) were fed isonitrogenous diet (10% protein) identical in all respects except in the nature of the protein source, for 4 weeks. Control group (group 1) had steamed mackerel meat as the protein source, whereas groups 2, 3 and 4 had mackerel fried on the 1st, 3rd and 4th days in the same coconut oil repeatedly used for frying each day. Four groups of adult male rats weighing around 130 g were fed on the same diet for 12 weeks. Weanlings fed on fish fried on the 4th day showed significantly lower feed consumption and weight gain compared to the other three groups. All the three groups of adult rats fed on fried fish compared well with control rats in weight gain and hepatosomatic index. There was a decrease in the total lipid and cholesterol content of the liver of rats fed with fried fish in comparison with the control rats. The total lipid and cholesterol in heart and serum cholesterol levels increased significantly from control rats through group 4. The C22:6/C20:5 ratio in the heart lipid showed a very high value compared to the dietary lipids. Histopathological examination showed initial stages of cell damage in the liver and kidney of rats fed with fish fried on the 4th day. In-vitro digestibility of proteins of fried fish were lower than that of steamed fish, but the difference in this respect between proteins of fish fried on different days was not significant.     

Dietary exposure of juvenile rainbow trout (Oncorhynchus mykiss) to 1,2-bis(2,4,6-tribromophenoxy)ethane: bioaccumulation parameters, biochemical effects, and metabolism

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed in the laboratory to an environmentally relevant dose of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) via their diet for 49 days, followed by 154 days of untreated food to examine bioaccumulation parameters, potential biochemical effects, and metabolic products. There was a linear increase in the amount of BTBPE in fish during the uptake phase of the experiment, and an uptake rate constant of 0.0069 +/- 0.0012 (arithmetic mean +/- 1 x standard error) nmoles per day was calculated. The elimination of BTBPE from the fish obeyed first-order depuration kinetics (r2 = 0.6427, p < 0.001) with a calculated half-life of 54.1 +/- 8.5 days. The derived biomagnification factor of 2.3 +/- 0.9 suggests that this chemical has a high potential for biomagnification in aquatic food webs. Debrominated and hydroxylated metabolites were not detected in liver extracts and suggest that either biotransformation or storage of BTBPE-metabolites in the hepatic system of fish is minor or that our exposure time frame was too short. Similar concentrations of circulating thyroid hormones, liver deiodinase enzyme activity, and thyroid glandular histology suggest that BTBPE is not a potent thyroid axis disruptor.     

EFFECT OF FEED DIET ON AMINOPEPTIDASE ACTIVITIES FROM THE HEPATOPANCREAS OF WHITE SHRIMP (PENAEUS VANNAMEI)

White shrimp (Penaeus vannamei) were fed one of seven diets for 30 days. Diets contained 85% of a reference ration and 15% of either anchovy, tuna waste meal, deboned fish meal, langostilla crab meal, soybean meal, menhaden meal A, or menhaden B as a protein replacer. At the end of the feeding trial, animals were sacrificed and 10 aminopeptidase activities of the hepatopancreas tissue were assayed. The hepatopancreas tissues contained Arg-, Leu-, His-, Ile-, Lys-, Met-, Thr- and Val-aminopeptidase activities but no activity was detected for Phe-aminopeptidase. Leu-aminopeptidase activity was inhibited by Zn⁺² and Mg⁺² salts and activity was also inhibited when more than 0.2 mg of hepatopancreas extract protein was included in the assay. Principal component analysis was used to determine whether diet had an influence on hepatopancreas
aminopeptidase activities. The aminopeptidase activities were greater for animals fed a diet containing menhaden fish meal B. This was principally the result of the higher levels of Met-, Val-, Pro-, Lys-, and Leu-aminopeptidase activities in animals fed menhaden fish meal. Menhaden fish meal B had a lower nutritional quality for shrimp than the other protein replacers. Seven of the 10 essential amino acids for shrimp were present at less than 100% of the recommended values. On the other hand, shrimp fed soybean meal replacer contained lower amounts of aminopeptidase activity, notably Gly- and Met-aminopeptidase activities, and the meal was of excellent quality having only one limiting amino acid. The results indicate that the shrimp diet can influence proteolytic activity of the hepatopancreas tissue. This is significant to the seafood technologist since previous studies showed that hepatopancreas proteases can leach into the meat postmortem and cause tissue softening.     

Effect of starvation and diet on the gel forming ability of tilapia (Oreochromis niloticus)

To elucidate the factors affecting the variation in the gel forming ability of fish muscle within a species, the effect of starvation and diet on the proximate composition and gelling property of tilapia muscle was examined. Starvation resulted in a decrease in protein and lipid contents coupled with an increase in water content. Protein depletion, mainly in the myofibrillar fraction, in the starved fish caused a lowering of the gel forming ability of their muscle. The myosin-degrading activity at 65°C was not affected by starvation for 56 days. Tilapia (Oreochromis niloticus L) fed on either fishmeal or krillmeal did not differ in their proximate composition. Phytoplankton-fed fish had a slightly higher lipid content and had the greatest gel forming ability. There was no significant difference in the gel strength between the fish fed fishmeal and the fish fed krill or 58 days. Compared with the phytoplankton, however, prolonged feeding of fishmeal seemed to increase the myosin-degrading activity of the muscle.     

Thyrotoxicity of sodium arsenate, sodium perchlorate, and their mixture in zebrafish Danio rerio

Both perchlorate and arsenate are environmental contaminants. Perchlorate is a definitive thyroid disruptor, and arsenic may disrupt thyroid homeostasis via multiple pathways. To evaluate the effects of sodium perchlorate and sodium arsenate on thyroid function and possible interactions between them, zebrafish (Danio rerio) were exposed to sodium perchlorate (10 and 100 mg/L), sodium arsenate (1 and 10 mg/L), and the mixture sodium perchlorate + sodium arsenate (10 + 1 and 100 + 10 mg/ L) for up to 90 days. At day 10, 30, 60, and 90, fish were sampled and analyzed forthyroid histopathological end points including follicular cell height, follicle size, colloid size, colloid depletion, hyperplasia, and angiogenesis. Effects on epithelial cell height (hypertrophy) were seen as early as 10 days after exposure. Perchlorate induced changes in all parameters staring at 30 days of exposure. Prolonged perchlorate exposure induced angiogenesis, a relatively new marker of thyroid disruption. Sodium arsenate was less effective than sodium perchlorate in causing thyroid histopathologies, but transient responses were seen for hypertrophy, hyperplasia, and colloid depletion (% colloid). This is the first report of arsenate-induced effects on thyroid histopathology. However, because statistically significant effects were not consistently seen in all end points, evidence for arsenate as a thyroid disruptor remains equivocal. In general, the sensitivity of the following histopathological indicators for indicating thyroid perturbations is, in descending order: follicular cell height > percent of colloid area/follicle area > colloid area/follicular cell height > hyperplasia > angiogenesis > colloid area >follicle area = fish growth.     

Perchlorate affects thyroid function in eastern mosquitofish (Gambusia holbrooki) at environmentally relevant concentrations

The purpose of this study was to determine the effects of perchlorate on thyroid function in mosquitofish. Adult mosquitofish were exposed to 0, 0.1, 1, 10, 100, and 1000 mg/L sodium perchlorate for 2, 10, and 30 d. Whole body thyroxin (T4) content and histological assessment of thyroid follicles (e.g., follicular epithelial height, hyperplasia, hypertrophy, and colloid depletion) were used to gauge alterations in thyroid function. Follicular epithelial cell height, hyperplasia, and hypertrophy increased with increasing perchlorate concentration, especially in fish exposed for 30 d, and these effects were statistically significantly different from control at concentrations as low as 0.1 mg/L (nominal concentration). The percent occurrence of follicles with depleted colloid decreased with increasing perchlorate concentration, which is contrary to what is expected with thyroid inhibition. There also was a decrease in whole body T4 concentration in fish exposed to perchlorate for 30 d, but clear dose-response relationships were less evident for whole body T4 than for histopathological endpoints. In conclusion, thyroid histopathology provides a sensitive biomarker for thyroid endocrine disruption at environmentally relevant concentrations of sodium perchlorate, and whole body T4 is a less sensitive indicator of perchlorate exposure than is histopathology.     

FISH OIL WITH ESSENCE OF CHICKEN DECREASES SERUM AND HEPATIC TRIACYLGLYCEROL IN HAMSTERS FED AN ATHEROGENIC DIET

The aim of the present study was to investigate the effect of a mixture of dietary chicken essence and fish oil on possible lowering of blood and hepatic lipids in hamsters. Forty male hamsters were randomly divided into four groups and fed a chow diet, high fat/cholesterol diet (HFC), HFC diets containing 4% (HFC4) or 8% (HFC8) fish oil with essence of chicken for 42 days. The experimental diets contained 10% (w/w) fat. Hamsters fed HFC diets containing either 4 or 8% fish oil with essence of chicken showed significantly decreased serum triacylglycerols (TG) compared to hamsters fed HFC diets. In addition, hamsters fed HFC8 diets exhibited significantly reduced hepatic TG than those fed HFC diet. However, hamsters fed HFC4 or HFC8 diets significantly increased low density lipoprotein cholesterol (LDL-C) and decreased high density lipoprotein cholesterol (HDL-C) when compared with those on HFC diet. These results suggest that 4% (or more) fish oil with essence of chicken might significantly lower serum TG and hepatic TG in hamsters, but seem to increase serum cholesterol levels on HFC diets.     

Adult-only exposure of male rats to a diet of high phytoestrogen content increases apoptosis of meiotic and post-meiotic germ cells

Apoptosis plays a critical role in regulating sperm production. Removal of androgens and gonadotropins, or estrogen administration induces germ cell apoptosis. It is hypothesized that dietary phytoestrogens increase apoptosis of developing germ cells, decreasing sperm production. This study aimed to test this in rats fed a high phytoestrogen diet only during adulthood. Male Wistar rats used in this study were offspring of females maintained on a low phytoestrogen diet prior to conception through to weaning. After weaning, juveniles were fed the same low phytoestrogen diet into adulthood. A cohort of males were transferred to a high phytoestrogen diet for 24 days and subsequently testes were collected from all animals. In the high phytoestrogen fed group, homogenization-resistant sperm counts were significantly decreased, as were epididymal sperm counts. Morphometric analysis determined round and elongated spermatid volumes to be significantly decreased, but seminiferous tubule lumen diameters to be significantly increased. TUNEL analysis determined that apoptosis of spermatocytes and round spermatids was significantly greater in the high phytoestrogen fed rats. Neither plasma gonadotropin concentrations nor testicular testosterone were altered. In conclusion, exposure of the adult male rat to a high phytoestrogen diet disrupts spermatogenesis, increasing germ cell apoptosis. This effect is independent of the hypothalamo-pituitary-testicular axis and is likely due to disruption of estrogen's actions in the testis.     

Hexabromocyclododecane in marine species from the Western Scheldt Estuary: diastereoisomer- and enantiomer-specific accumulation

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant, which is increasingly reported in the environment. Here, we report on the diastereomeric and, for the first time, on the enantiomeric composition of HBCD in muscle and liver of several fish species caught in the Western Scheldt Estuary (The Netherlands). The total HBCD content (sum of alpha-, beta-, and gamma-diastereoisomers), as well as the distribution of diastereoisomers and enantiomers, varied between the species. The levels of total HBCD (9-1110 ng/g lipid weight) found in fish tissues were higher than those measured in fish from European rivers with no known point sources of HBCD but lower than in fish samples collected near factories producing or using HBCD. The concentrations of total HBCD expressed on a lipid weight basis were higher in liver than in muscle for bib and whiting, while in sole, HBCD had no preferential distribution between the tissues. A similar pattern for liver and muscle distribution was already observed for polybrominated diphenyl ethers (PBDEs) in these species. The alpha-HBCD diastereoisomer was most abundant in all fish samples with a higher contribution to the total HBCD levels in liver compared to muscle for bib and whiting. The gamma-HBCD diastereoisomer accumulated less in liver than in muscle of sole, bib, and whiting. For the first time, enantiomer fractions were determined for HBCD diastereoisomers in liver of three fish species and in muscle of two fish species. A significant enrichment of the (+) alpha-HBCD enantiomer was found in whiting and bib liver samples. A high enantioselectivity has also been seen for the gamma-HBCD diastereoisomer in whiting liver.     

Effect of feeding restricted amounts of a medium and a high protein diet during the finishing period on growth,fat deposition and feed efficiency of male and female broilers

An experiment is described in which male and female broilers were fed either a 20 or a 23% crude protein diet, at 4 levels of intake—ad libitum and about 96, 92 and 87% of ad libitum—from 35 to 56 or 60 days of age. Males ate more, grew faster and converted food to body weight more efficiently than females. Male carcasses were significantly leaner than female carcasses at market age. On average, birds fed the high-protein diet ate a similar amount of food, grew at a slightly slower rate and converted food to body weight significantly less efficiently than birds fed the medium-protein diet. Carcass dry matter of birds fed the high-protein diet contained only about two percentage points less ether extract than that of those fed the medium protein diet. Growth rate and feed efficiency in the 35- to 56-day period decreased as the feed allowance was reduced. Groups fed the lowest level of food intake were kept until 60 days of age, when live weight was similar but carcasses were somewhat leaner than those of ad libitum groups at 56 days. In spite of the similarity in final live weight and lower body fat content, food conversion in the 35- to 60-day period for birds fed the lowest level of food intake was less efficient than that for ad libitum groups in the shorter 35- to 56-day period.     

Toxicokinetics and carry-over model of α-hexabromocyclododecane (HBCD) from feed to consumption-sized Atlantic salmon (Salmo salar)

A two-compartmental model for the kinetics of carry-over of the brominated flame retardant α-hexabromocyclododecane (HBCD) from feed to the fillet of farmed harvest-sized Atlantic salmon (Salmo salar L.) was developed. The model is based on a fat compartment for storage of the lipophilic α-HBCD and a central compartment comprising all other tissues. Specific for this model is that the salmon has a continuous growth and that fillet contaminant levels are explained by both the fat and the central compartments. The uptake and elimination kinetics are obtained from experimental data where consumer sized (start weight approximately 1 kg) Atlantic salmon was fed α-HBCD spiked feed (280 ± 11 μg kg(-1)) for 2 months followed by a depuration period of 3 months. The model was used to simulate the HBCD feed-to-fillet transfer in Atlantic salmon under realistic farming conditions such as the seasonal fluctuations in feed intake, growth and fillet fat deposition. The model predictions gave fillet concentrations of 0.2-1.8 μg kg(-1) depending on the level of fish oil inclusion in the salmon diets when using fish oil with high POP background levels. Model simulations show that currently farmed Atlantic salmon can contribute to a maximum of 6% of the estimated provisional food reference dose for HBCD.     

Bioaccumulation, biotransformation, and biochemical effects of brominated diphenyl ethers in juvenile lake trout (Salvelinus namaycush)

Juvenile lake trout (Salvelinus namaycush) were exposed to three dietary concentrations (0, approximately 2.5, and approximately 25 ng/g per BDE congener) of 13 BDE congeners (3-10 Br atoms) in the laboratory for 56 days, followed by 112 days of clean food, to examine bioaccumulation parameters and potential biochemical effects. The bioaccumulation of BDEs by the trout was highly influenced by biotransformation, via debromination, which resulted in bioaccumulation parameters that were much different than would be expected based on studies of chlorinated organic compounds (e.g., PCBs). Half-lives (t1/2's) for some BDE congeners (e.g., BDE-85 and -190) were much lower than expected based on their Kow, which was likely due to biotransformation, whereas t1/2's of other BDE congeners (e.g., BDE-66, -77, -153, and -154) were much longer than anticipated based on Kow. This was likely because the metabolites of BDE formed via debromination had the same chemical structure of these BDE congeners, which supplemented measured concentrations. The detection of three BDE congeners (an unknown penta, BDE-140, and an unknown hexa) in the fish that were not present in the food or in the control fish provide further evidence forthe debromination of BDEs. Half-lives of BDEs ranged from 38 +/- 9 to 346 +/- 173 days and biomagnification factors ranged from 1.6 (BDE-190) to 45.9 (BDE-100), but these bioaccumulation parameters need to be viewed with caution because they were highly influenced by debromination and relative abundance of individual BDEs that the fish were exposed to. CYP1A enzyme activity, measured as EROD, and free tri-iodothyronine (T3) concentrations in the plasma of lake trout varied significantly throughout the experiment but were not related to BDE exposure. In contrast, plasma levels of thyroxine levels (T4) were lower in both groups of PBDE-exposed fish compared with control fish after 56 days of exposure, and after 168 days in the high dose, suggesting that PBDEs may influence thyroid homeostasis at levels that are higher than what is normally found in the environment.     

Texture Properties of Farmed Rainbow Trout (Oncorhynchus mykiss): Effects of Diet,Muscle Fat Content and Time of Storage on Ice

Groups of rainbow trout (Oncorhynchus mykiss) fed diets with low or high fat content were stored on ice for up to 11 days in two separate experiments. After 4, 9 and 11 days storage on ice in the first experiment and after 5, 8 and 11 days in the second experiment the fish were filleted by hand and fillet gaping was evaluated. Texture properties were studied using an Instron compression test. pH was measured in all fillets. In fillets from the second experiment, also fat content and autolytic protease activity were measured. Diet affected fillet fat content and texture properties. Fish fed high fat diet exerted less resistance against compression, indicating a softer consistency. Force at yield point and slope were not significantly affected by diet. The high fat group had higher autolytic protease activity than the low fat group. The results from the Instron measurements indicated that the fish became softer and less tough during 11 days storage on ice. A slight, but statistically significant increase in pH with time was observed in both experiments. In the first experiment a reduction in gaping scores was observed during storage, as opposed to a significant increase in the second experiment. The texture parameters yield point and slope were negatively correlated to gaping in the second experiment.     

Toxicokinetics and carry-over model of α-hexabromocyclododecane (HBCD) from feed to consumption-sized Atlantic salmon (Salmo salar)

A two-compartmental model for the kinetics of carry-over of the brominated flame retardant α-hexabromocyclododecane (HBCD) from feed to the fillet of farmed harvest-sized Atlantic salmon (Salmo salar L.) was developed. The model is based on a fat compartment for storage of the lipophilic α-HBCD and a central compartment comprising all other tissues. Specific for this model is that the salmon has a continuous growth and that fillet contaminant levels are explained by both the fat and the central compartments. The uptake and elimination kinetics are obtained from experimental data where consumer sized (start weight approximately 1?kg) Atlantic salmon was fed α-HBCD spiked feed (280?±?11?µg?kg^?1) for 2 months followed by a depuration period of 3 months. The model was used to simulate the HBCD feed-to-fillet transfer in Atlantic salmon under realistic farming conditions such as the seasonal fluctuations in feed intake, growth and fillet fat deposition. The model predictions gave fillet concentrations of 0.2–1.8?µg?kg^?1 depending on the level of fish oil inclusion in the salmon diets when using fish oil with high POP background levels. Model simulations show that currently farmed Atlantic salmon can contribute to a maximum of 6% of the estimated provisional food reference dose for HBCD.     

Effect of low level monensin supplementation on the production of dairy cows fed alfalfa silage

Effectiveness of low level monensin supplementation on N utilization in lactating dairy cows fed alfalfa silage was assessed using 48 multiparous Holsteins. Cows were fed a covariate diet [% of dry matter (DM): 56% alfalfa silage, 39% ground high moisture corn, 3% soybean meal, 1% ground corn, 1% vitamin-mineral supplements] for 2 wk, then grouped by days in milk into blocks of 4. Cows were randomly assigned within blocks to 1 of 4 diets that were fed for 10 wk: 1) control (covariate diet), 2) control plus 3% fish meal (replacing DM from high moisture corn), 3) monensin (10 mg/kg DM), and 4) monensin plus 3% fish meal. Diets 1 and 3 averaged 16.7% crude protein (25% from free AA in alfalfa silage); diets 2 and 4 averaged 18.5% crude protein. Monensin intake averaged 16 mg/d on diets 1 and 2 (due to contamination) and 248 mg/d on diets 3 and 4. There was no effect of fish meal or monensin on DM intake. However, weight gain and yield of milk, protein, and SNF increased with fish meal feeding, indicating metabolizable protein limited production. Feeding monensin increased blood glucose but reduced yield of 3.5% fat-corrected milk, milk fat content and yield, and milk protein content and yield. Apparent N efficiency was greatest on monensin (diet 3) but lowest on monensin plus fish meal (diet 4). Fish meal reduced blood glucose concentration and apparent N efficiency, and increased concentrations of milk and blood urea. Monensin increased ruminal propionate concentration and decreased concentration of acetate and butyrate and acetate:propionate in ruminally cannulated cows fed the experimental diets. However, these changes were small, suggesting that too little monensin was fed. Fish meal reduced ruminal total amino acid (AA) but monensin did not alter ruminal NH(3) or total AA. Both fish meal and monensin increased NH(3) formation from casein AA using ruminal inoculum from the cannulated cows. There was no evidence from this trial that feeding 250 mg of monensin per day to lactating cows improved N utilization by reducing ruminal catabolism of the large amounts of free AA in alfalfa silage.     

Effect of grain level and protein source on ruminal fermentation, degradability, and digestion in milking cows fed silage

Five primiparous Holstein cows (483 kg BW) of low productivity were used in a 4 x 5 incomplete Latin square design to study the effects of feeding two levels of grain containing soybean meal and one level of grain containing fish meal on feed intake, milk production, digestibility, and rumen fermentation. Animals all were fed alfalfa silage for ad libitum intake. Collection of data was between wk 11 and 24 of lactation. The four treatments were an all silage diet (control), silage and medium concentrate fed at 1.8% BW containing soybean meal, and silage and low concentrate fed at 1.3% BW containing either soybean meal or fish meal. Treatments other than control were designed to give similar CP intake from the concentrate, which was based on high moisture corn and cob meal. Milk production and composition were similar among treatments except for fat percentage, which was significantly lower for low grain soybean meal. Intake of DM was higher on medium grain soybean meal compared with the other treatments. Average BW and change in BW (.11 kg/d) were not affected by treatments. Digestibility of DM was higher for cows fed grain (68 to 73%) than for those fed the control diet (60%). Generally, feeding concentrate at 1.3 or 1.8% BW and supplementing with soybean meal or fish meal resulted in pH and concentrations of NH3 N and VFA similar to those observed on the all silage diet. Feeding concentrate at 1.3 or 1.8% BW and supplying fish meal or soybean meal did not change feed utilization enough to increase milk production in low producing cows compared with an all silage diet.     

Yield, Lipid, Cholesterol and Fatty Acid Composition of Spent Hens Fed Full-Fat Oil Seeds and Fish Meal Diets

Yield, proximate and fatty acids composition of white and dark meats and whole carcasses were determined in spent hens fed flax or canola seeds, fish meal and a control diet. Live weights and percent carcass cut-up yield were not affected by the diets fed. However, hens fed flax seed diets contained significantly (P< 0.05) lower levels of cholesterol in the dark meat than the control group. The inclusion of oil seeds, in particular flax seeds in the hens diet, enriched the meats with omega-3 fatty acids (C18:3ω>3; C20:5ω3; C22:5ω3). Omega-3 fatty acids enriched poultry meats from spent hens could be useful in the development of “health oriented” further processed poultry products.     

Effects of dietary methylmercury on reproduction of fathead minnows

We examined effects of dietary methylmercury (MeHg) on reproduction of fathead minnows (Pimephales promelas). Juvenile fish were fed one of four diets until sexual maturity (phase 1): a control diet (0.06 microg Hg g(-1) dry weight) and three diets contaminated with MeHg at 0.88 (low), 4.11 (medium), and 8.46 microg Hg g(-1) dry weight (high). At sexual maturity, male and female fish were paired, again fed one of the four diets, and allowed to reproduce (phase 2). To assess effects of MeHg during gametogenesis, some fish were fed diets during phase 2 that differed from those during phase 1. Spawning success of pairs fed the same diet during phases 1 and 2 was 75% for controls and 46%, 50%, and 36% for the low-, medium-, and high-MeHg treatments, respectively. Spawning success of pairs fed a contaminated diet during phase 1 and a control diet during phase 2 was 63%, 40%, and 14% for the low-, medium-, and high-MeHg treatments, respectively, whereas exposure to dietary MeHg only during phase 2 did not reduce spawning success. Dietary MeHg delayed spawning, and days to spawning was positively correlated with concentration of total mercury in the carcasses of test fish. MeHg reduced the instantaneous rate of reproduction of fish fed the same diets during phases 1 and 2. Both the gonadosomatic index and reproductive effort of female fish were inversely correlated with mercury in carcasses, whereas developmental and hatching success of embryos, 7-d survival, and 7-d growth of larvae were unrelated to mercury concentrations in parental fish or their diets. MeHg decreased reproduction of adult fathead minnows at dietary concentrations encountered by predatory fishes in aquatic systems with MeHg-contaminated food webs, implying that exposed fish populations could be adversely affected by this widespread contaminant.