Logic Assessing Research on Bass in the Potomac River

What problem were the researchers investigating?

The research was undertaken to assess whether the location of fish, specifically smallmouth bass and largemouth bass, downstream from wastewater treatment plants, is influencing the biological development of the fish with reference to the presence of cells associated with female reproductive systems developing on the testis of male fish.

Give the background of the problem

In 2003 a study was undertaken which identified that between 33% and 80% of the smallmouth bass in the South Branch of the Potomac river had some developmental abnormalities, with the presence of oocytes on the male fish testis. Oocytes are he cells which will develop into ovum for reproduction in females, and are usually absent in males. With the testicular oocytes observed on fish collected across different areas of the South Branch of the river it would appear that there was a causal factor impacting on the biological development of the fish. The results do not appear to have been flawed, as a subsequent study looking only at the Shenandoah Rover found even higher rates of this biological abnormality.

This abnormality is not totally unknown, it has been recorded before, but it is an unusual characteristic. The appearance of testicular oocytes is some types of fish are usually associated with exposure to certain types of chemicals which can interfere with the release of hormones into the bloodstream. The appearance of oocytes on the testis of fish is usually accepted as a biological market of certain types of chemical being present in the water. While the link between chemical exposure and the testicular abnormality has been established, there has not been any proof that the chemical which can cause this are in the Potomac.

It was also known that there was a waste water treatment plant on the Potomac, in other areas these are known to be one of several potential sources of the chemical which interfere with the hormones of the fish, but it is not a source that...

Describe the researchers observations of the fish and their environment.
All of the fish collected were observed as being sexually mature, meaning that any sexual development expected had taken place. 51 fish were collected from 5 different sites, two sets where collected upstream and downstream of waste water treatment plants and the fifth from a non-associated site. The fish were assessed in terms of their sexual development; it was found that the fish at all test sites displayed characteristics associated with chemicals that interfered with sexual development; however the scale of the impact varied. Details are given in the study if the different measures that were undertaken, including the blood samples, with a complete breakdown of the results.

4. What methods did the researchers use to pursue their investigation?

The methodology was to take fish from five sites, two sets of site upstream and downstream of two waste water treatment plants on Conococheague Creek and Monocacy River, and a third site where not waste water treatment plant was situated. The aim was to collect 30 fish at each site, with the aim of ensuring there 10 ten of each gender from each site. The fish collected at the downstream sites were within 1 km of the waste water treatment plants, and the distance between the downstream and the upstream collection points was at least 15 km. The fish were caught in 2005 between September 5th and 14th. Once caught the fish were killed with a fatal dose of tricaine methane sulfonate. The fish were weighed and measured onsite with bloods drawn and transferred to secure containers for transportation and examination. The methodology involved assessing the fish and then undertaking a comparison analysis.

5. Was the study reliable? Do you have any criticisms about the research, if so, what are they?

The study has a number of characteristics which indicate that it is reliable. The methodology which is used is designed in a logical manner; it involves the assessment of male and female…