Critique of:

Belova, N.V., B.V. Verigin, N.G. Yemel'yanova, A.P. Makeyeva, and I.N. Ryabov. Radiobiological analysis of silver carp (Hypophthalmichthys molitrix) from the cooling pond of the Chernobyl nuclear power station in the post-disaster period. I. Reproductive system of fish exposed to radioactive contamination. J. Ichthyol. 34(4):16-38.

The title tells the main focus of the research article, the effects of radiobiological contamination on the reproductive systems of silver carp after the Chernobyl explosion. The title sparks the interest of the reader with the words Chernobyl and Post-Disaster period. However, the title lacks continuity in going from the analysis of silver carp to the reproductive systems of fish. It could be reworded so that it would flow better to create an even more appealing article, such as "An Investigation of the Effects of Radioactive Contamination from the Chernobyl Explosion on the Reproductive Systems of Silver Carp".

AUTHORS

Each of the researchers listed as authors of the research article, Belova, Verigin, Yemel'yanova, Makeyeva, and Ryabov, all have literature cited in the text of the article. The previous work of all the researchers has been on some aspect of silver carp, carp, or minnow reproduction or on the impact of radioactive contaminants on hydrobionts near Chernobyl. This indicates that they have a background in the area of silver carp reproduction and radioactive contamination to base their current research on. It also bolsters their credibility as researchers because each has published research papers, which is not necessarily an easy task.

ABSTRACT

The abstract states the focus of the research, the study of gonadal morphology and function in silver carp exposed to radioactivity, but it does not actually summarize the content of the article. It does not tell how the researchers studied morphology and function of the reproductive systems of the silver carp, and it does not hint at any of the conclusions that the experimenters reached. These points, when included in an abstract, make the article seem worth reading but unfortunately this abstract seemingly points to a dull research article. To improve the abstract, the authors could include more about how they determined if gonadal abmormalities were due to radiation and about the conclusions that were derived from the results.

INTRODUCTION

The first 7 paragraphs of the introduction give background information on the concern over the effects of radiation on the environment and on organisms, particularly on silver carp that were in the cooling pond of the Chernobyl Power Station when it exploded. In the experiment, the researchers wanted to determine the effects of the high amounts of radiation from the explosion on the gonads of silver carp. The experimental set-up was designed so that previous experimental data on the normal reproductive functions of silver carp in natural-radiation conditions would serve as the control of the experiment. Any abnormalities found in the gonads of silver carp would be assumed to be due to the high amounts of radiation emitted from the Chernobyl explosion. My objection is that the authors did not include any of this data for the reader to compare to the experimental results. How can the reader evaluate whether the results of the experiment are significant if there is no information to compare it to?

The next section of the introduction tells about the cooling pond and the conditions affecting the fish, such as temperature and hydrochemical parameters, the icthyofauna in the pool, and information on radiation. This section is informational and provides much background material that leads up to the problem that the experiment will try to shed light on, the effects of radiation on the gonads of silver carp. This experiment is to be a continuation of previous work done on the effects of the Chernobyl disaster.

Overall, the introduction is informitive and it explains why the authors are conducting the experiment. It would have been helpful to have more information on the normal reproductive systems of silver carp so that a better evaluation of the results could be performed by the reader.

MATERIALS AND METHODS

This section tells how the experimenters gathered their data. The sample sizes that they used for each year from 1989 to 1992 to monitor changes in reproductive system functioning and morphology were too small to produce any significant results that could be generalized to the entire population of silver carp in existence. A total of 89 fish was used in the entire study over a four year period because the total number of fish in the pond was limited (no exact number was given). Since the sample size was small and the population in the pond was limited, we can assume that the results are typical of the silver carp population in the pond. However,in order to be able to generalize data to the entire population, a large sample size must be used in gathering data. A large sample will eliminate factors that may otherwise tip the results in a small sample size, leading the researchers to false conclusions. Due to the small sample size used in the study, the results cannot be interpreted as representing the entire population of silver carp. Knowing what percent of the total population of silver carp the 89 fish represented may shed some light on whether the data can be generalized to the entire population or not.

The methods used to histologically examine the specimens are consistent with modern capabilities in research. The authors did not indicate how they determined the gonadal quality and maturity, whether by just looking at slides or by some other means. An explanation of this would give more insight into the results.

RESULTS

In the results section, there were many tables and figures that were not labeled sufficiently, had information in them that was not referred to in the body of the article, or had data that were not explained in the text. In table 1, the data for the measurements of body shape and internal organs is shown, but there is no explanation as to why these data were included. Also in table 1, there were 2 columns headed GSI and Clark's condition factor. The authors did not tell what GSI or Clark's factor stand for or how they were calculated. Clark's factor was not mentioned in the body of the body of the text. Another problem with table 1 is that the stages of sexual maturity, I and II for example, are not defined and therefore the significance of the stages cannot be used by the reader to evaluate the data. In table 2, the gonadal anomaly column is not clearly labeled as to whether the gonadal anomaly data is in numbers or percentage.

Table 3 looks as if it contains significant data, but upon closer inspection, the effects of using a small sample size are obvious. In the table, the column headed by the number of specimens with abnormalities has data on the percent of specimens with abnormalities. If the reader looks at the sample sizes, 8, 6, 7, 4, for males, and then looks at the percentage with abnormalities, it is evident that the results are not accurate. Therefore the results are not as significant as the authors portray in the body of the discussion. There was one typing error in table 3. Under the heading of % with abnormalities, there is no column for females.

The results indicate the findings from the histological analysis of tissues from the gonads of silver carp. The findings were consistent with the expected results, that there would be gonadal abnormalities due to exposure to high radiation doses. However, the high percentages of fish with gonadal abnormalities were due to the fact that such a small sample size was used. Therefore, the results cannot be generalized to the larger population.

DISCUSSION

The authors say that they observed a gradual increase in the number of males with abnormal gonads. What they did not realize or were trying to cover up was the fact that the sample sizes decreased with each passing year so that in calculating perentage of males with abnormal gonads, the percentages increased. This again brings up the importance of a large sample size. The data for this increase cannot be used to generalize to the entire population because the sample sizes were too small. To counter the problem of small sample size and render the results significant for the entire population, the researchers would have had to test a larger population of silver carp.

In this section, the authors tried to argue that since both carp and goldfish become sterile when exposed to high levels of radiation, and some silver carp were found to be sterile, that all fish become sterile after

exposure to several hundred roentgens of radiation. Due to the small sample size used for the study, the authors cannot make sweeping statements because the sample population was not representative of the entire fish population referred to in the text, and it was not representative of other species of fish. In order to support a statement such as this one, the researchers would have to test more species than just silver carp and they would have to test large sample sizes of them.

An abnormality found in gonads, swellings and narrowings, were said to definitily be related to radiation effects (p. 31). Other causes of these abnormalities were not investigated therefore the validity of this statement must be questioned. In order to support this, the researchers would have to run another experiment that would eliminate other variables that may cause gonadal abnormalities, to determine if these abnormalities were indeed caused by radiation.

CONCLUSIONS

The authors concluded that the radiation dose the fish received over the four year period was responsible for the increasing numbers of fish with gonadal abnormalities. These abnormalities were produced in part by the radiation, however, the authors did not take into account other factors that may have also produced the results that they obtained. Other environmental factors, diet, and others were not considered.

The authors said that the high fecundity of the silver carp counterbalanced the effects of the radiation. In other words that because the carp were still able to reproduce at normal levels (which are condsidered high) that this allowed the population to thrive even with high levels of radiation. Fecundity was not measured in the experiment in this article but in another experiment conducted at the same time and with some of the same specimens. The other experiment had not been written up at the time that this experiment was. These conclusions should not be included in the write up of this experiment since the data are not available for the other experiment and there is no citation because the experiment has not been adequately recorded. Also these conclusions should not be included because they data that led to them were not directly from this experiment.

LITERATURE CITED

The authors seemed to have a good knowledge of the topics related to the experiment, and used many citations that were fairly recent (from the 1980's). There were a few problems with the citations. Some of the citations were not listed in the literature cited section: Kryshev et al., 1993, Shabadash, 1957, Shekhanova, 1977, Rybakov et al., 1987, and Plyukhin, 1987. Perhaps they were forgotten or they are not existing research articles.

Overall, this is an interesting experiment that took advantage of the Chernobyl disaster to research the effects of radiation on fish. I made comments throughout this critique about the problems that I found with the experimental set-up, results, discussion of the results, and conclusions, and some ways the authors could have improved their research.