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Impacts of Cypermethrin and Deltamethrin’s Use on Aquatic Invertebrates in Commercial Aquaculture Ponds

MD. MOKHLESUR RAHMAN
Institute of Environmental Science, University of Rajshahi, Rajshahi 6205, Bangladesh

M. NAZRUL ISLAM
Department of Zoology, University of Rajshahi, Rajshahi-6205, Bangladesh

Abstract/ Executive Summary:

Agricultural pyrethroid insecticides especially cypermethrin and deltamethrin are being used regularly for the control of aquatic insects in commercial carp aquaculture ponds in northwest Bangladesh. This study was conducted in a farmer’s ponds under commercial aquaculture to know the impact of cypermethrin and deltamethrin on aquatic invertebrates (insects, zooplanktons and benthos). Commercial aquaculture ponds were treated with cypermethrin and deltamethrin @ 5 μg (active ingredient)/liter pond water in presence of fish. Required amount of each of the insecticides were diluted with water in big aluminium pots and broadcasted over the pond water. Water quality parameters of the experimental ponds were measured at pretreatment stage. Sampling of aquatic in vertebrates was done pretreatment and after 1 day, 2 days, 5 days, 10 days, 15 days, 21days and 28 days of the application of insecticides. No fish mortality was recorded after the treatment. Aquatic insect population was found to be most affected;number count declined89.87% and 86.24% for cypermethrin and deltamethrin respectively within one day after treatment. The insect count recovery began after day 10 and day 5 of cypermethrin and deltamethr in treatment respectively. Loss of insect diversity was observed in cypermethrin treatment and diversity count did not recover within observation period of 28 days.Zooplankton population was relatively less impacted (21.10% and 26.33% declined respectively in cypermethrin and deltamethrin treatment). Benthos population count and diversity was not affected, possibly due to the high organic carbon content and clay soil of the pond bottom.

Keywords: Pyrethroids, Cypermethrin, Deltamethrin, Aquatic invertebrates

Location: The ponds under commercial aquaculture in Hatgodagari area of Poba Upazilla of Rajshahi district, Bangladesh

Start Date: 00-11-2018

End Date: 00-03-2019

Program Area: Animal Health and Management

Commodity: Aquatic animal

Objectives:

To understand the impact of cypermethrin and deltamethrin’s use on aquatic insect, zooplankton and benthos populations of ponds in northwest Bangladesh as practiced by the farmers.

Methodology:

The study was conducted in ponds under commercial aquaculture in Hatgodagari area of Poba Upazilla of Rajshahi district. Farmers were asked to inform the author before using pesticides in their ponds so that the author could conduct the study. Accordingly, a farmer informed the author prior to using cypermethrin (brand name Ripcord, BASF Bangladesh ltd., distributed by Padma Oil Company limited) and deltamethrin (brand name Desis, marketed by Bayer Crop Science limited Bangladesh) in commercial aquaculture ponds measured over 2 acres in size (water area) respectively in November 2018 and March 2019 @5μg (active ingredient)/liter pond water for both insecticides.Before the use of the insecticides water quality parameters of the treatment ponds were measured. Soil samples from the bottom of both experimental ponds were collected at pretreatment stage, sun dried, grounded, and tested for organic carbon content by the Soil Resource Development Institute (SRDI) laboratory in Rajshahi. Required quantity of both insecticides were diluted with water in a large aluminium pots and manually broadcasted along the water’s edge of the whole pond. The farmer made sure that no supplementary feed was supplied to the fish on the treatment day and the following day. The sampling of zooplankton, aquatic insects and benthos was done before the treatment and on days 1, 2, 5, 10, 15, 21, 28 following the cypermethrin and deltamethrin treatment. Sampling of aquatic insects: A one square meter fine meshed net fitted in a bamboo frame was used for sampling of aquatic insects. The net was towed in the water along the edges of the pond for a three-meter distance. Then the accumulated insects from the net were transferred to a plastic container containing water and 10 ml of formalin was added. The sampling process was repeated three times to be considered as three replications for sampling of both treatments. Sampling of zooplankton: A funnel shaped plankton net with specificationsof75 to 85 microns mesh size was fitted with a collecting bottle on the tapering end and a round metal frame on the open end. During each sampling the plankton net was towed for a 13-meter distance in the water, one foot below the surface. Then the sample was transferred to a plastic bottle and 5 ml formalin was added. The collected samples were transferred to the lab, where the total volume was measured, representing the amount of zooplankton per volume of water the net was traversed through and calculated using following formula: Water volume in liter= ‘ (3.14)’ multiplied by the‘square radius of the plankton net metal frame in meters’ multiplied by the‘ distance the net traversed through in meters’ multiplied by 1000. Zooplankton were identified and counted using a Sedge wick rafter cell counter (Welch 1948) and microscope. Sampling of benthos: A metal scoop with a 38.7 square centimeter opening was used to collect the soil samples from the bottom of the pond at 30-centimeter depth from the surface of the water. The process was repeated three times during each sampling to be considered as three replications for both treatments. In the lab, the collected soil samples were put under running tap water on a fine meshed sieve, through which all soil particle was washed away and the separated benthos samples were collected.

Source of Information: Bangladesh J. Fish. (2019) 31(2) : 211-220

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Water pH in both treatments was found to be around 7.5. Water turbidity was higher (43.19 ntu) in the deltamethrin treated pond than in cypermethrin treated pond (28.05 ntu). Electrical conductivity was also higher in deltamethrin treatment (516 μS/cm) than in cypermethrin treatment (310 μS/cm). Organic carbon content of the pond bottom soil was 2.19 and 3.40% (dry weight basis) respectively for cypermethrin and deltamethrin treatment. Within one day after use of cypermethrin and deltamethrin, the total insect count went down (90 and 86% respectively for cypermethrin and deltamethrin) for both treatments to reach to their lowest point of the study period. The total insect count for deltamethrin treatment went up sharply above the pretreatment level five days after the treatment and continued to beat a near static level until the end of the observation period. Increase of the insect-count in cypermethrin treatment was much slower compared to the deltamethrin treatment and did notrecover to pretreatment levels within the observation period. Insect diversity went down after use of cypermethrin in the aquaculture pond. Insect diversity was lowest at day-2 after the use of cypermethrin. The diversity gradually increased up to six types of insects at the end of the observation period of 28 days, while eight types of insect were recorded at pretreatment stage.

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