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Contact information on the participants appears at the end.
Mark Rigby, a sea bass, turbot and dover sole farmer and consultant on recirculating systems in the United Kingdom, started the discussion with the following questions:
Are EPDM (Ethylene-Propylene-Diene-Monomer) plastic liners toxic to shrimp?
Does anyone know if there is a problem with butyl rubber liners? We already use them with fish with no problems and want to run a few experimental tanks with very high density Penaeus vannamei.
Tzachi Samocha, a shrimp researcher at the Texas Agriculural Experiment Station, Shrimp Mariculture Research Facility, Corpus Christi, Texas, USA: Over the last few years we have conducted several studies concerning the toxicity of EPDM liners. In one study, we documented a toxic effect when an EPDM liner was used in an intensive recirculating system for shrimp (see Horowitz, A., Samocha, T.M., Gandy, R.L. and Horowitz, S. 2001. Toxicity test to assess the effect of synthetic tank liner on shrimp survival and nitrification in a recirculating super-intensive production system. Aquacultural Engineering 24:91-105).
More recent studies with Pacific white shrimp show that not all EPDM liners are equal:
1. Samocha, T.M., Patnaik, S., Horowitz, A. and Horowitz, S. 2004. The effect of different synthetic polymer liners on growth, survival and selected water quality indicators in tank-system stocked with Penaeus vannamei under limited discharge and in the presence of natural productivity. Book of Abstracts, World Aquaculture Society Annual Meeting, March 1-5, 2004, Honolulu, HI, USA.
2. Horowitz, A., Samocha, T.M., Patnaik, S. and Horowitz, S. 2004. A microbial-based toxicity test for synthetic polymers of potential use in aquaculture. Book of Abstracts, World Aquaculture Society Annual Meeting, March 1-5, 2004, Honolulu, HI, USA.
When comparing EPDM and HDPE (High Density Polyethylene) liners under limited discharge conditions, no differences were found in shrimp survival, but in terms of growth, some of the EPDM liners performed better than the HDPE liners. Nevertheless, growth of the shrimp in the control group (no liners) was a little better than any of the liner treatments.
Phil Boeing, a shrimp farming consultant in California, USA: The issue of materials toxicity to aquaculture organisms has been an ongoing discussion for decades. Judith Stein discussed the numerous compounds that are toxic to marine algae, and butyl rubber was one of them.
I always bioassay liner candidates with a couple simple tests. The first is to culture algae in the liner material and in a glass container. Be patient, it may take a few days. You will be checking for division rate and cell count differences over time. If you compare the liner material on two algae generaa flagellate and a diatom, for example, which have different susceptibilities to various chemicals, you might be able to calibrate the potential toxicity of your liners a little better.
I also like to use an embryo bioassay with any fertilized mollusk eggs (mussels, sea urchins, oysters, clams, abalone) that might be handy. If you dont have access to mollusk eggs, then early-stage, fertilized, shrimp eggs will work. Be sure you have a control for this assay in a non-liner container. You are looking for the survival rate of fertilized eggs to first stage larvae. Toxicity should manifest itself more clearly in bivalve larvae with either low or zero hatching in the presence of toxicity, while the shrimp eggs may develop abnormal setae and other deformities as well as survival differences in relation to controls.
Expose the liners in question to direct sunlight (and associated heat) for a few days before assaying. If there are any volatile compounds in the liner, this treatment can force them to expose themselves in the subsequent assay. Good luck.
Durwood Dugger, a shrimp farming consultant in Florida, USA: All EDPMs are not equal and may vary significantly chemically. As suggested, you should always perform a bioassay on your specific liner productusing the species you intend to culture. Our experience is that many materials have problems if they are not washed thoroughly before use. Problems with EDPMs may not be with the liner itself, but with post manufacture ingredients (anti-sticking compounds or curing residues) on their surfaceand that is why they either need to be weathered or washed before use (same with PVC). In our work, EDPM liners performed as well as HDPE liners, both in side-by-side bioassays and in lined nursery tanks and ponds. Firestone produces EDPM liners and has tested its product extensively. Contact John Heathcote (ljheathcote@FirestoneBP.com) for more information.
Dipi Ghumman, manager of a shrimp farm in Thailand: Thanks Mr. Durwood Dugger for your response on pond liners. It cleared up some of my doubts and made me more inclined to try them. Your suggestion to clean the liners thoroughly before use makes a lot of sense.
Oscar Hennig, manager of The Oceanic Institutes shrimp hatchery on the island of Hawaii, USA: We lined two ponds and a couple of raceways with HDPE liners, and the majority of our tanks are made with HDPE. Its the only liner material that I have experience with. I would like to see more responses on how EDPM compares to HDPE?
Durwood Dugger: Material-wise the EDPM is usually more expensive than HDPE for the same thickness and area. With HDPE, however, you have to have special equipment to weld seams. One fusion welder might cost $15,000. The welders are also high maintenance items and require artful adjustment to keep them from frying and puncturing the liner. Also, no glue or adhesive repair material bonds to HDPE permanently. Its like Teflon. HDPE is so slick that birds can not stand on a 2:1 slope of it.
EDPM, on the other hand, can be bonded with a solvent cement and seaming tape, a process very similar to patching the inner tube on a bicycle tire. And EDPM is far more flexible than a similar thickness of HDPE, so its far easier to unroll, fit to contours and install, especially in tight corners and turns around pipes and drains. It took a crew of six professionals almost a week to install HDPE liners in one of our 220 x 76 x 6 raceways. It took one day to do an identical raceway in EDPM with two experienced installers and inexperienced help. The message here is to examine and compare your total cost for materials and installation. Depending on your specific situation, one material may be less expensive than the other. And remember that I am not exaggerating the difficulty in repairing the HDPE without a fusion welder. The repair problem grows as the HDPE material ages and becomes less and less weldable.
Oscar Hennig: Durwood, thanks for your time and your explanation about EDPM liners. Youre right about the HDPE welders requiring artful adjustment. We have burned our share of pond liners here.
Mark Rigby: Thank you to everyone who responded regarding tank liners. I am still very interested in more information on butyl rubber, which is in common use for fish tank liners, where it is the material of choice due to its longevity (indoors) and flexibility. It can be heat welded or glued. A made-to-measure, 3.5-meter-diameter by 1.5-meter-high, tank liner (0.75 mm thickness) cost us $442. This is about the same cost, but much less work, than our other option, epoxy coating the tanks (galvanized metal rings on concrete base).
(In Alphabetical Order)
Phil Boeing, Phil Boeing, Shrimp Consultant, 53-300 Avenida Navarro, La Quinta, CA 92253 USA (phone 760-564-1421, email firstname.lastname@example.org).
Durwood Dugger, President, BioCepts International, Inc., 947 Sandpiper Lane, Vero Beach, FL 32963 USA (phone 772-332-1046, fax 772-234-8966, email email@example.com, webpage http://www.biocepts.com).
Dipi Ghumman, Sikao-Kontikki Shrimp Farm, Thai-Madan Aquaculture Farms, 136/45 Udomlarp Soi 7, Thanon Rongrien Thabthieng, Thabthieng, Amphur Muang, Trang, Thailand 92000 (cell phone 66-1668-3711, office phone 66-7522-0416, email firstname.lastname@example.org).
Oscar L. Hennig, The Oceanic Institute, Research Associate, Kona Site Manager, P.O. Box 1423, Kailua-Kona, HI 96745 USA (phone/fax 808-329-9293, email email@example.com).
Mark Rigby, Llyn Aquaculture, Ltd., Afonwen Farm, Chwilog, Pwllheli, Gwynedd, Wales, United Kingdom LL53 6TX (phone 01766 810904, fax 01766 810904, email mark.@aquacommerce.com, webpage http://www.aquacommerce.sageweb.co.uk/).
Tzachi Samocha, Ph.D., Professor Texas Agricultural Experiment Station, Shrimp Mariculture Research Facility, 4301 Waldron Road, Corpus Christi, TX 78418 USA (phone 361-937-2268, fax 361-937-6470, email firstname.lastname@example.org, webpage, http://ccag.tamu.edu/FlourBluff/flour.htm).
Sources: 1. The Shrimp List. Subject: Pond Liners. November 25 to 29, 2004. 2. Summarized by Bob Rosenberry, Shrimp News International, October 1, 2005
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