Arthur C. Potts and Curtis M. Jolly

Chlorination of ponds has been suggested as a treatment by Alabama farmers to reduce fish losses due to waterborne diseases. Recent AAES research indicates the use of chlorine in catfish ponds is of marginal economic value and in some cases may be a detriment. The rationale for this practice is that chlorine reduces levels of coliform bacteria and some other pathogens in drinking water; thus, it can also be used to reduce the levels and numbers of pathogens in water used for fish production. The reasoning behind this may be dangerous since the unguided use of chlorine may be injurious to both humans and fish.

Since farmers' use of chlorine to control infectious diseases may be based on observations from their neighbors, it was important to determine the extent to which farmers have embraced this practice, and the possible effects of use of chlorine on fish production and the environment. A survey was developed by AAES researchers to determine chlorine use and its impact on catfish production.

The survey reached 179 active Alabama catfish farmers. These farmers were spread out over 31 counties with the majority in Hale county, which is home to 67 fish farmers. Of the 59 fish farmers responding, 22 of them (37% of the respondents) revealed that they had used chlorine in catfish ponds, while the remaining 37 (63%) fish farmers have not treated their fish ponds with chlorine.

The majority (36.6%) of users said they received the information on chlorine use from other farmers, while 18.18% stated that they received information from a private consultant. Only 13.64% of the farmers said they received information from the Extension System. Extension specialists recommend chlorine use only for the disinfection of catfish ponds. About 9.09% of the farmers reporting the use of chlorine said they received the information from the literature, 9.09% said information on chlorine-use was obtained from processors, while 13.64% did not reveal their source of information.

The rate of application of chlorine ranged from 0.05 parts per million (ppm) in treating catfish production ponds to 7.44 ppm in the disinfection of ponds. Thirteen of the 22 farmers using chlorine did so at rates less than 1 ppm; in fact, few treated at rates above 2 ppm. Four farmers have treated at rates greater than 5 ppm. Some farmers who used chlorine gave no indication as to their treatment rates. The frequency of treatment varied, ranging from as low as once per year (disinfectant) to numerous times per week during the growing season.

The application rates of chlorine were divided into four sub-categories: a disinfectant applied at 0.46 to 7.44 ppm; above recommended rates, from 0.23 to 0.28 ppm; recommended range from 0.10 to 0.18 ppm; and below recommended range, less than 0.10 ppm. No significant differences in mortality for the four levels of application were indicated. There were no significant differences in yields for the different ranges of total amount of chlorine applied and fish yield. The same result was obtained for mortality and total chlorine applied.

Fifty-four percent (54.5%) of the respondents broadcast chlorine into their ponds, throwing the chlorine randomly into the pond, often from a boat; 36.4% applied chlorine along the shoreline, throwing the chlorine on the shoreline from the pond banks; and 4.5% used the "hotspot method," applying the chlorine to specific areas in the pond with excessive algal bloom. The average application rate of the shoreline applicators was 0.13 ppm chlorine and 1.56 ppm for those who broadcast the chlorine. Farmers who broadcast the chlorine revealed slightly lower yields per acre (5,748 per pound) than farmers who applied the chlorine on the shoreline (average yield of 6,046 per pound per acre). The yield for farmers who applied their chlorine by the shoreline had no statistically significant difference in yields from farmers who broadcast the chlorine. There was also no difference in mortality rate when method of application was considered.

Simple correlation disclosed that there was no relationship between the concentration of chlorine applied and the yield of fish per acre stated by farmers. There was also no significant correlation between mortality declared by farmers and the concentration level nor the frequency of application. There was no statistical difference among the 19 farmers who provided information on their yields and levels of concentration of chlorine and those who stated that they never used chlorine in their fish ponds. The average yield of farmers who reported using chlorine was 8,342 pounds per acre and the average yield of those not using was 8,053 pounds per acre.

Using an enterprise budget for a 100-acre commercial catfish operation for Alabama, calculations were made to determine the net benefit of using chlorine. Since there were no significant differences in yields of catfish for farmers using and not using chlorine, it was assumed that farm revenue did not change by the addition of chlorine, but the variable cost increased.

The use of chlorine as a disinfectant increased variable cost from $216,846.07 to $255,555.59, an 18.0% increase, which reduced net income per acre from $741.34 to $354.25 (see the table). If chlorine was used at above recommend rate, with no significant change in production, variable cost was increased by 8% and net returns per acre were reduced by 22%.

Cost, Returns, and Break-even Prices for 100-acre Commercial Catfish Enterprise in Alabama, Recommended Practices and With Chlorine Added at Various Rates, 1997^1,2

Item	Cost and returns recommended practices	Chlorine added
		as disinfectant	above recommended rate3	at recommended rate	below recommended rate
Gross receipt	$351,025.8	$351,025.8	$351,025.8	$351,025.8	$351,025.8
Variable cost	216,846.1	255555.6	232,873.4	235,378.0	221,607.7
Income above variable cost	134,179.7	95,470.2	118,152.4	115,647.9	129,418.1
Fixed cost	60,045.5	60,045.5	60,045.5	60,045.5	60,045.5
Total cost	276,891.6	315,601.1	292,919.0	295,423.4	281,653.2
Net returns above all costs	74,134.3	35,424.7	58,106.9	55,602.4	69,372.6
Net returns per acre	741.3	354.3	581.1	556.0	693.7
Break-even price to cover variable cost	43.2¢	51.1¢	46.6¢	47.1¢	44.3¢
Break-even price to cover total cost	55.2¢	63.1¢	58.6¢	59.2¢	56.3¢
1The data for the recommended practices were taken from a 100-acre enterprise budget for a commercial operation for Alabama prepared by J. Crews and M. Masser. The information for chlorine addition to the pond was based on average used by farmers. The rates of chlorine used in the calculation are based on average rates farmers stated they used on their farms during the interview in 1996. 2Sawyer, C.N. and P.L. McCarty. 1967. Chemistry for Sanitary Engineers. McGraw-Hill, Inc., New York. Snoeyink, V.L. and D. Jenkins. 1980. Water Chemistry. John Wiley and Sons Inc., New York. 3 Above recommended rate ranged from 0.23 to 0.28 ppm. However, since farmers applied chlorine more frequently at the recommended rate, the total amount of chlorine was more than the above recommended rate. This affected the cost of chlorine used per acre.

The addition of chlorine at the recommended rate increased variable cost by 9%, which resulted in a decline in net returns per acre of 25%. At below the recommended rate net returns per acre fell by 7%. The use of chlorine as a disinfectant increased the break-even price to cover variable cost from 43.2 cents per pound to 51.1 cents. When used above the recommended rate, break-even price to cover variable cost increased by 3.84 cents per pound.

The use of chlorine can affect short-term survival of the farm if the selling price per pound falls below 60 cents and the farmer is using it as a disinfectant. The break-even price to cover total cost when chlorine was used as a disinfectant increased to 63.1 cents. Hence farmers either use chlorine as a disinfectant or as a preventive measure for reducing the incidence of diseases, without any clear indication of its net benefits to fish production and farm revenue.

The use of chlorine as a preventive or curative measure in fish production is complex since very little is known about how chlorine affects water quality and how it reacts with other substances in the pond bottom. A number of factors promote the disinfection resistance of bacteria on surfaces in chlorinated water. The pond environment has organic matter that tends to deactivate much of the chlorine added, especially if added in low concentrations (as low as 2.00 mg/l). It is doubtful, therefore, whether the use of small doses of chlorine is beneficial to catfish farmers. If enough chlorine is applied to produce a residual of chlorine compounds of sufficient concentration to kill fish pathogens, phytoplankton, and nonpathogenic bacteria in the water, there is a high probability that fish stress or toxicity will result.

A number of bacteria are resistant to chlorine and its derivatives at doses much higher than that which will kill catfish. The aerobic bacteria group, which often causes losses to catfish farmers, are highly resistant to chlorine. Therefore, present rates of chlorine application may be of no positive economic importance to catfish farmers, and farmers might be killing more fish than increasing their yields. Chlorine use in aquaculture is approved by the Food and Drug Administration (FDA) for disinfection only. Chlorine applied in any other way is not recommended.