Photo: Hashime MurayamaDes expériences scientifiques en laboratoire ont confirmé que le fumier de poulet dans l'eau affecte le développement sexuel des poissons. Leur étude pourrait faire le lien entre les conditions qui entravent au sexe du poisson et le fumier de poulet qui est épandu sur les terres agricoles.
L'étude s'est penché sur l'achigan à grande bouche dans 6 lacs et étangs de la péninsule Delmarva au Maryland dans la région Eastern Shore depuis 2 ans. Des poissons mâles portaient des oeufs, selon les scientifiques de l'Université du Maryland. C'est la première fois que l'on rapporte des poissons intersexuels à cet endroit, bien que des chercheurs avaient trouvé la même chose il y a quelques années dans l'achigan à petite bouche dans la Potomac et ses tributaires, et tout récemment des achigans à petite bouche dans la rivière Susquehanna.
L'existence des poissons intersexuels est préoccupante, disent les scientifiques, parce qu'ils pourraient être des indicateurs de contaminants dans l'eau qui nuisent à leur croissance et leur reproduction. Le nombre et l'état des poissons intersexués trouvés dans Eastern Shore ne sont pas aussi graves que ceux du Potomac ou de la Susquehana selon les scientifiques, mais cela semble être chose répandue, du moins dans la population d'achigan à grande bouche dans les lacs et étangs de la péninsule: "Nous en avons trouvé dans tous les lacs où nous avons regardé." dit Daniel J. Fisher, le chercheur en chef "Nous avons trouvé des poissons intersexuels dans tous les lacs, et le pourcentage qui souffrait de la condition anormale allait de 33% à 100% des poissons prélevés."
Dans des tests en laboratoire à part, les chercheurs de l'U du M. disent qu'ils ont trouvé des alevins qui montraient des signes de problèmes sexuels et de croissance quand ils étaient mis en contact avec de l'eau contaminée avec des excréments de volaille. Avec l'aide de d'autres chercheurs, ils ont élevés 3 espèces de poissons en laboratoire pendant 3 semaines dans de l'eau dosée avec les stéroïdes sexuels produits par des poules femelles. Bien que 2 des espèces en ont très peu souffert, la troisième avait des changements dans leurs gonades, leurs organes sexuels, et les alevins étaient féménisés considérablement. Les stéroïdes ou hormones des tests en labo sont des hormones produits naturellement par les volailles et non pas venant des substances dans la moulée de ces animaux, mais ont été détectés dans les excréments des volailles ainsi que dans les ruisseaux après les pluies du printemps.
La litière des volailles, un mélange d'excréments et de bran de scie, est épandue sur les champs agricoles comme engrais. L'EPA a déjà dénoncé le ruissellement des engrais chimiques et des fumiers venant des champs agricoles comme la principale source majeure de polluants du Chesapeake Bay.
On s'inquiète d'ailleurs déjà que l'arsenic ajouté à la moulée des volailles par certains éleveurs pourrait provoquer les problèmes intersexuels des poissons. L'arsenic est utilisé pour contrôler les parasites dans la volaille et est seulement l'un des plusieurs produits chimiques trouvés à des basses concentrations dans certains cours d'eau que les scientifiques suspectent comme jouant un rôle de perturbateur endocrinien, pouvant nuire à la croissance, à la reproduction et à la résistance aux maladies.
Dans certaines rivières où l'on a constaté que les achigans à petite bouche intersexuels étaient présents souffraient aussi d'une baisse de la population dans le bassin versant de ces rivières. Les poissons intersexués semblent se trouver un peu partout aux États-Unis. Une étude l'an passé a constaté la présence de poissons mâles avec des oeufs dans leurs testicules dans 9 rivières au travers les É.-U. Ils sembles être surtout dans les rivières du sud-est, et surtout chez les achigans. On n'est pas sûr pourquoi les achigans sont particulièrement sujets à ce problème.
Les scientifiques se doutent que l'intersexualité chez les poissons est probablement liée aux contaminants dans les rivières, les ruisseaux et les lacs. Les chercheurs ont pu reproduire le problème chez les poissons en les mettant en contact avec des produits chimiques qui agissent comme des hormones et peuvent déranger la croissance de l'animal, sa capacité de se reproduire ou son système immunitaire. Parmis les contaminants les plus mis en doute sont les pesticides, les produits pharmaceutiques (médicaments), les produits de beauté et les excréments d'animaux. Ces produits se retrouvent tous dans les cours d'eau, bien que les chercheurs n'ont pas réussi à prouver un lien de cause à effet avec la condition d'intersexualité, les problèmes de reproduction ou la maladie chez le poisson.
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"Intersex fish found in Delmarva lakes
In lab studies, scientists also find fish affected by poultry waste in water
Scientists have found more intersex fish in Maryland, this time on the Eastern Shore, and their research suggests one possible source of the gender-bending condition could be the poultry manure that is widely used there to fertilize croplands.
Six lakes and ponds on the Delmarva Peninsula sampled over the past two years have yielded male largemouth bass carrying eggs, according to University of Maryland scientists. Those are the first intersex fish reported there, though researchers found the condition several years ago in smallmouth bass in the Potomac and its tributaries, and recently found it in smallmouth bass in the Susquehanna.
Intersex fish are a concern, scientists say, because they could be indicators of contaminants in the water, affecting their growth and reproduction.
The intersex condition in the Shore fish is not as severe as it is among fish from the Potomac or Susquehanna, the researchers said, but it appears to be widespread, at least in largemouth bass in the peninsula's lakes and ponds. "We find it in every lake that we look," said Daniel J. Fisher, senior research scientist at UM's Wye Research and Education Center in Queenstown. "We found fish with intersex in all of the lakes, and the percentage [with the condition] ranged from 33 percent of fish we sampled to 100 percent."
The Maryland lakes checked were Tuckahoe in Queen Anne's County and Smithville and Williston in Caroline County. In Delaware, Hearns Pond in Sussex County and Moores Lake and McColley Pond in Kent County were sampled. The sampling was performed under a grant from the U.S. Environmental Protection Agency.
In separate laboratory tests, the UM researchers said, they found the sex and development of certain juvenile fish were affected when exposed to water contaminated with poultry waste.
Working with other scientists, the UM researchers kept three species of laboratory fish — fathead minnows, sheepshead minnows and mummichogs — for three weeks in water dosed with the sex steroids produced by female chickens. While two of the species showed little or no effect, fathead minnows displayed changes in their gonads, or sex organs, and larval minnows experienced "pronounced feminization." Assistant research scientist Lance T. Yonkos, Fisher and other colleagues reported their findings in October's Environmental Toxicology and Chemistry journal.
Fisher stressed that the steroids or hormones used in the lab tests were produced by the chickens naturally and were not substances fed to the animals. "We've actually measured those hormones in waste material," Fisher said. The substances have been detected in Delmarva streams after spring rains, he said.
Roughly 600 million chickens are raised annually on the Delmarva Peninsula. Estimates of the waste generated by them vary, from 600,000 tons to 1 million tons or more. Much of that poultry "litter," chicken manure mixed with wood shavings, is spread on croplands as fertilizer. The EPA has identified runoff of chemical fertilizer and manure from farm fields as a major source of the pollutants fouling the Chesapeake Bay.
Concerns have been raised about the possibility that arsenic added to chicken feed by some growers could trigger such intersex conditions in fish. Arsenic, used to control parasites in chickens, is just one of a variety of chemicals found at low levels in some waters that scientists say can act as an endocrine disruptor, potentially interfering with growth, reproduction and disease resistance. Environmental activists this week declared they would renew efforts to get Maryland lawmakers to ban the use of arsenic in chicken feed in the state.
But Fisher and Yonkos said they haven't detected arsenic in runoff from manure-fertilized farm fields they sampled, and they've only picked up the toxic chemical in one batch of poultry litter they sampled directly. Yonkos noted that the poultry manure they've used in their research has come mainly from growers raising chickens for Perdue Farms. The Salisbury-based poultry company has said it stopped adding arsenic-containing roxarsone to its birds' feed several years ago.
William Satterfield, executive director of Delmarva Poultry Industry Inc., representing many of the more than 1,600 growers on the peninsula, said the laboratory setup under which fish were exposed to poultry-waste hormones "seems extreme and not representative of real-world conditions. The levels being used by the researchers seem unrealistically high." Fisher said the levels of hormones to which fish were exposed were similar to what researchers have measured in runoff from fields. But he acknowledged that the lab tests may not mirror water-quality conditions fish experience in the wild, where pollution may come in pulses and not remain constant for three weeks at a time. That's why, he added in an email, "We now are going to streams and lakes in the 'real' world outside the lab to see if we see anything happening there."
Don Cosden, assistant fisheries director with the Maryland Department of Natural Resources, said the finding of intersex largemouth bass on the Shore was "a little surprising," since the condition had seemed limited mainly to smallmouth bass in the Potomac and Susquehanna watersheds. Cosden said largemouth and smallmouth bass populations declined in Shore rivers several years ago after drought made the water saltier, forcing the fresh-water fish farther upstream. There'd been no reports of die-offs or illness — until lately, when officials discovered a virus particular to largemouth bass in rivers on the Shore and in the Potomac. The UM researchers did check some Shore streams, Yonkos said, but didn't find many intersex fish. Then again, he said, they didn't find that many male largemouth bass.
Roger Tragesar, president of the Maryland Bass Federation, said his group's members are concerned about reports of intersex bass, but still unclear what if anything they may mean to the health or abundance of the fish. "I don't think we're flip-flopping or losing a lot of sleep over it just yet," Tragesar said, "but we certainly want people to stay focused on it and do everything they can to determine why this is happening." Intersex smallmouth bass were first detected by accident in the Potomac River seven years ago as scientists were investigating fish kills and lesions there. The same intersex condition turned up subsequently in fish in the South Branch of the Potomac, the Shenandoah and the Monacacy.
Vicki S. Blazer, a U.S. Geological Survey scientist who found those intersex fish, this year found the trait in smallmouth bass caught in the Susquehanna River and in the Juniata River. Biologists had noted a drop in young smallmouth bass in that watershed in recent years. Intersex fish appear to be fairly widespread, though. A U.S. Geological Survey study published last year found male fish with eggs in their testes in nine rivers nationwide. The trait was most common in the Southeast, and particularly in bass. "The largemouth and smallmouth bass do seem to be more prone to the condition," said Jo Ellen Hinck, lead author of that study. "But we're not sure why. We do not know what is causing it."
Scientists suspect that the intersex fish may be linked to contaminants found in rivers, streams and lakes. Researchers have been able to induce the condition in fish by exposing them to a wide variety of chemicals or mixtures that act like hormones and can disrupt an animal's development, reproduction or immune system. Among the suspected contaminants are pesticides, pharmaceuticals, personal care products and animal waste. They have all been widely found in water ways, though researchers have yet to prove any connection with the intersex condition, reproductive problems or illness in fish."
Excerpts from article written by Timothy B. Wheeler from The Baltimore Sun published here:
http://www.baltimoresun.com/features/green/bs-gr-intersex-fish-shore-20101111,0,4527836.story
Also in Nature, chemicals in wastewater affect fish: http://www.nature.com/news/2010/101112/full/news.2010.607.html
One has to wonder if these same chemicals affect human reproduction, and would there be a link with people having problems falling pregnant, or the low sperm count in modern man?
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