Dedicated To Tribal Aquaculture Programs
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March 1994 ~ Volume 7 | |
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Topics of Interest:
Swim Bladder Inflation in Walleyes
Survey of Swim Bladder Inflation in Walleyes Reared in Hatchery Production Ponds
By: Greg A. Kindschi and Frederic T. Barrows, U.S. Fish and Wildlife Service Bozeman Fish Technology Center, Bozeman, MT 406-587-9265
Noninflation of swim bladders in intensively reared larval walleyes has been identified as a problem in culturing this species. Walleyes inflate their swim bladders somewhere between days 7 and 14 posthatch when they are reared at a water temperature of 15NC. These physoclistous fish must gulp atmospheric air to initiate the inflation process. Any factor that prevents them from gulping air and reaching the air-water interface, will prevent the initial inflation and the normal development of the swim bladder. Physoclistous fish will survive in captivity without inflated swim bladders; however, they are in much poorer condition than fish with normally inflated swim bladders. Prior to our survey of production facilities, there were no documented cases of pond-reared walleyes exhibiting uninflated swim bladders.
Barrows determined that spraying water on the water surface in circular rearing tanks can significantly increase swim bladder inflation rates among larval walleyes compared with rates in unsprayed tanks. The increase in surface water turbulence may allow fish to gulp air or it may prevent buildup of a surface film of feed or oil that can inhibit gas exchange.
Young walleyes depend on zooplankton as their initial food source, and zooplankton density is a major factor affecting survival and growth rate. Walleyes without inflated swim bladders must expend a great deal more energy to capture prey than fish with inflated bladders, and they are more susceptible to stress. Consequently, survival of fish lacking an inflated swim bladder may be reduced, particularly after fish are distributed in the wild. If pond-reared walleyes without inflated swim bladders are observed frequently, the probability is high that survival rates and overall fish quality are suffering. The objective of this study was to determine the extent to which noninflation of swim bladders occurs among pond-reared walleyes raised at hatcheries around the USA.
Results and Discussion
We examined 120,064 walleye fingerlings from 188 ponds at 15 facilities in nine states. Only 3.5% (4,229) of the fish examined during the 3 years lacked an inflated swim bladder, but the incidence reached 55.3% in one pond. Fish with uninflated swim bladders were observed in 101 of the 188 ponds sampled (53.7%).
Walleye fingerlings with inflated swim bladders were longer and weighed more than walleyes from the same pond with uninflated bladders. Fingerlings examined had been reared in ponds from 24 to 56 days posthatch. There seemed to be no relation between size of fish at harvest and the incidence of swim bladder noninflation in any pond. Walleye with inflated swim bladders averaged 2.45% body fat, whereas fish lacking an inflated swim bladder averaged 1.45% body fat. This difference in fat content might have occurred for two reasons. First, fish lacking an inflated swim bladder may not have been able to capture as much food as the normal fish and thus were unable to build up fat stores. Second, fish lacking an inflated swim bladder may have been capturing as much food as normal fish, but expending so much energy in doing so that fat stores did not develop as fully.
A small percentage (not recorded) of walleyes with uninflated swim bladders exhibited lordotic (spinal) deformities. Kitajima observed this anomaly in striped bass and suggested it was a result of the uninflated swim bladder. We concur with this observation and feel these confounding factors would impede survival.
The stocking of pond-reared walleyes that lack inflated swim bladders may partially explain why certain year-classes do not survive well after distribution. Even though only 3.5% of the walleye fingerlings examined in this survey exhibited uninflated bladders, the problem occurred in over half of the 188 ponds sampled and at all of the 15 facilities. We feel this indicates that uninflated walleye swim bladders is a significant abnormality that warrants further monitoring and evaluation to ensure production of quality fish. Barrows determined that a water surface spray dramatically improved the inflation rates of intensively reared walleye fry, and this may prove to be a method for alleviating uninflation problems in ponds as well. During the swim bladder inflation period (7-14 days posthatch), if there is no wind, a pond surface spray of water may help break up the surface film and aid in the inflation process.
Recording other hatchery information relevant to pond production such as weather, water quality, fertilization rate and type, forage available, brood-stock origin, egg incubation temperature and period, pond design, and chemicals used, may all be beneficial in case any of these factors contributes to swim bladder noninflation. This information was informally collected during this survey but no relation could be determined between these and the lack of swim bladder inflation. A simple sampling and diagnostic procedure when ponds are harvested would identify walleye swim bladder inflation rates before fish are distributed.
Effects of Surface Water Spray, Diet, and Phase Feeding on Swim Bladder Inflation, Survival, and Cost of Production of Intensively Reared Larval Walleyes
By: Frederic T. Barrows, Ronald E. Zitzow, and Greg A. Kindschi, U.S. Fish and Wildlife Service, Bozeman Fish Technology Center, Bozeman, MT
Walleye eggs have been collected, incubated, hatched, and stocked into various waters since the late 1800s. Walleye fingerlings have been reared with formulated feeds since 1971, and research into the intensive culture of walleye fry has been conducted since approximately 1973. Efforts to intensively culture fry with formulated feeds have met with poor survival and low levels of swim bladder inflation. Greater survival was obtained by Hokanson and Lien (1986), but practical rearing densities and conditions (i.e., formulated feed) were not used. Walleyes must inflate their swim bladders sometime between days 7 and 15 posthatch, when reared at 70NF; inflation will not occur later. Walleyes without inflated swim bladders can be identified by their vigorous swimming and head-up orientations. Even when swim bladder inflation rates of 57-60% were obtained, survival rates were still less than 10% by day 21.
Using a deep cylindrical rearing system, we conducted three trials in 1991. The objectives of these trials were (1) to determine if a spray of water onto the surface of the rearing tank would increase swim bladder inflation, (2) to determine the effect of feeding various commercial larval feeds on survival and swim bladder inflation, and (3) to determine the effect of phase feeding-giving first a high-quality starter diet, then a lower cost commercial or experimental diet-on survival, swim bladder inflation, and growth.
Results and Discussion
Experiment 1: Surface Spraying
A layer of oil and fine feed particles developed on the water surface of tanks not receiving spray. Spraying water on the surface prevented this layer from developing. The spray did not affect fish length, production, or survival. Swim bladder inflation was determined after 30 days on feed, and the inflation rate therefore was influenced by mortality during that period. The true inflation rate would be best determined immediately following the inflation period, approximately day 15. The practical measurement includes mortality that may or may not be influenced by inflation status. In the present trial, swim bladder inflation was higher for the fish reared in tanks receiving spray (98.4%) than for fish in tanks without spray (51.7%). The improvement in swim bladder inflation when the oil and feed layer on the water surface was dispersed supports the hypothesis that walleye must gulp air to initially inflate their bladders.
Experiment 2: Diet Comparisons
Diet affected the growth and survival of walleye fry. Fry fed BioKyowa-B were larger and had a higher survival rate (33.1%) than fry fed EPAC (San Francisco Bay Brand) or Larval AP200 (Zeigler). There was no effect of diet on swim bladder inflation; fry fed BioKyowa-B or EPAC had 95-100% bladder inflation rates. Each of the three tanks receiving AP200 were drained on day 9 posthatch, because only a few fish remained and none were feeding. The small particle size of AP200 might have been responsible for high mortality due to poor feed consumption, although some fish were observed with feed in their gastrointestinal tracts. Diet BioKyowa-B is expensive on a per kilogram basis, but it is a very effective first feed for walleyes.
Experiment 3: Phase Feeding
Diets BioKyowa-C and WS9112 (manufactured at Bozeman Fish Technology Center) were readily consumed by walleye fry after they had been fed BioKyowa-B for 7 days. Survival at the end of the 30 day trial was similar for fish fed BioKyowa-B, BioKyowa-C, or WS9112 during phase 2 (30-33%). There was no difference in final length or swim bladder inflation among fish on the various diet regimens. A considerable economic advantage was realized with the phase-feeding technique. Overall feed cost per fish produced was 76% less for the fish shifted to BioKyowa-C than for the fish kept on BioKyowa-B throughout the trial. The cost of WS9112 cannot be calculated because some of the ingredients were manufactured in the laboratory. We estimate that production-scale costs of WS9112 would be similar to those of BioKyowa-C.
Diet regimen affected the body composition of walleyes. The fish fed WS9112 in phase 2 had less body protein and more body fat than fish on the other two diet regimens and they grew less, suggesting an imbalance in the protein and energy levels of WS9112. However, WS9112 is an open-formula diet that, with the present manufacturing methods, ingredient choice, and binding system, adequately supports growth and survival of larval walleyes. We have tested numerous other laboratory-scale diet manufacturing techniques, and WS9112 is the only one to support survival of larval walleyes as well as the BioKyowa-B diet does.
Protecting Genetic Resources of Aquatic Organisms: Elimination of Stock Transfers
By: David Philipp, John Epifanio, and Martin Jennings
As a follow-up to the "Eggs Apples and Fish" article MTAN published in our December newsletter, we wanted to provide our readers with another perspective regarding this issue. The following article (shortened to conserve space) was published in the December 1993 issue of Fisheries, a bulletin of the American Fisheries Society.
Issue Definition
The culture and introduction of aquatic organisms have been used by managers to enhance fisheries throughout North America for well over 100 years. Introductions can be classified into three types: (1) introduction of a species into an area in which it previously did not occur naturally (termed non-native introduction); (2) introduction of individuals from one stock of a given species into waters inhabited by another, genetically distinct stock of the same species (termed stock transfer); and (3) reintroduction of individuals cultured from one stock into waters inhabited by that same stock (termed genetically compatible introduction). Throughout this position statement, stock is used as the operational unit of genetic and management concern.
The potential dangers associated with the introduction of non-native species have become well-recognized by biologists. The genetic integrity of local stocks, acquired as a result of the evolutionary processes that lead to differentiation and adaptation, is now at risk. However, if we are to conserve the biological diversity of our aquatic resources on a long-term basis, that genetic integrity needs to be protected.
Technical Background
Genetic Resources
Genetic variation within a species can be partitioned into two distinct components: (1) intrastock variability, i.e., among individuals within a stock; and (2) inter-stock variability, i.e., among stocks. Because both components of variation are important to the evolutionary process, new efforts to protect aquatic organisms from actions that would reduce either type of genetic variation are necessary for the long-term survival of species.
Genetic variation among individuals within a stock is the raw material upon which natural selection acts. Loss of genetic variation within a stock reduces the adaptive potential of that stock. Risks associated with a loss of this type increase greatly as a consequence of small effective population size because of the heightened potential for inbreeding and genetic drift. Culture and management programs that incorporate genetics theory can minimize those risks; however, many public and private culture programs still neglect this important task. Several authors have reviewed the evidence documenting that ignoring genetic principles can reduce the genetic variability of hatchery stocks of fish.
Genetic variation among stocks represents the evolutionary product of their becoming genetically tailored to the different environments they inhabit. That is, fish species generally occur as groups of related, yet distinct stocks rather than as single, randomly mating panmictic units. Because local environments vary in physical, chemical, and biological characteristics, each environment has a unique suite of characteristics that affects a different selection regime on the organisms that inhabit it. Further, because fitness is maximized through the process of natural selection, individuals acquire adaptations that make them better suited to the specific environments they inhabit.
Among diverging stocks, gene combinations that prove advantageous in each different environment become established, eventually forming coadapted gene complexes. Disruption of these favorable complexes results from the interbreeding that commonly follows a stock transfer and can produce individuals that are less "fit" for the local environment. This decline in overall fitness, known as outbreeding depression, may increase among individuals of successive generations. Although natural selection will act on the novel gene combinations that would occur after introgressive hybridization, the result of that process is unpredictable. Furthermore, restoration of fitness to preintroduction levels, even if achieved, may require many generations, and the coadapted gene complexes that previously existed may be irretrievable.
Stock Concept of Management
According to the stock concept of management, a species typically is comprised of multiple, genetically distinct groups (stocks) that have diverged from other such groups as a result of temporal, spatial, or behavioral isolation. Thus, the stock, rather than the species as a whole, needs to be considered the operational unit of management concern. Although the identification of all stocks within any single species has yet to be completed, there is overwhelming evidence to indicate that genetically divergent units occur within many, if not all, fish species.
A consensus on the criteria that define a stock has yet to be achieved among biologists. However, if the genetic resources of native species are to be protected, actions to curtail stock transfers cannot wait for absolute refinement of such criteria, emergence of unequivocal methods for assessing divergence, or development of more complete data bases.
Stocking Procedures
Each state, provincial, tribal, and federal government in North America has its own culture system, and many aquatic organisms are introduced annually into waters within its jurisdiction. Because so many distinct bodies of water currently receive introductions of aquatic organisms, donor broodstock often originate from a body of water other than the one actually receiving the introduction. These activities are usually conducted to satisfy specific short-term goals, but the longer-term ecological and genetic consequences of such introductions on recipient stocks have seldom been considered.
Three scenarios illustrate the kinds of problems that can occur because of unwise stocking practices. First, single hatcheries can serve expansive geographic regions, as is the case with many federal system hatcheries, and as a result, recipient stocks are often geographically distant from the source of the donor broodstock. Second, in times of "need," a state, province, or individual facility may trade excess production of one species to another agency or facility in exchange for individuals of some different species for which production fell short. Third, many private hatcheries produce aquatic organisms for an undefined and unregulated private clientele that may introduce them or permit their escapement into waters containing wild populations of those same organisms. All three scenarios represent stock transfers that can have deleterious effects on the genetic structure of native aquatic organisms.
Course of Action
Because stocking programs can harm the genetic resources of native aquatic organisms, the American Fisheries Society urges federal, state, tribal, and provincial fisheries agencies as well as the private sector to:
(1) evaluate current culture and enhancement practices to develop new management programs that will protect the biodiversity of aquatic natural resources by eliminating stock transfers within their jurisdiction;
(2) eliminate any "trading system" designed to meet quotas for achieving production goals in which agencies exchange organisms of different species or stocks resulting in stock transfer;
(3) develop more stringent regulations governing the production, sale, and transport of aquatic organisms by the private sector and promote the adequate enforcement of those regulations to prevent intentional or accidental introductions into waters containing native stocks;
(4) cooperate in achieving a consensus on the criteria that define a stock and lead in developing informational data bases that include assessment of genetic variation among stocks of native sport and non-game aquatic species;
(5) form species-level working groups for all managed aquatic species that will:
a. propose boundaries describing component native stocks and recommend preferred protocols that relate to introductions,
b. identify areas that would be designated as genetic reserves to be specifically managed to prevent contamination from stock transfers, and
c. assess management goals and objectives to develop ecologically and genetically based management plans for each species.
(6) develop a public education program to promote public awareness of the issues involved and public acceptance of the proposed management strategies.
Effectiveness of Therapeutic Salt Treatments for Preventing Transport of Zebra Mussels With Hatchery Fish
By: Diane Waller, John Crowther, and Jeff Rach National Fisheries Research Center, La Crosse, WI
The zebra mussel is spreading progressively through the waterways of North America and threatens major rivers and inland lakes. One potential mechanism for overland dispersal of the mussels is the transport of baits and hatchery-reared fishes. The transport of early life stages of the mussel is of particular concern to hatchery personnel. The larvae, or veliger, is planktonic and remains suspended in the water column for several weeks. These early life stages are microscopic and can occur in high densities. Consequently, large numbers of larval mussels can be inadvertently transported as veligers with fish and introduced into stocked streams, lakes, ponds, and other fish-holding facilities. There, the veliger may settle and metamorphose to a plantigrade mussel.
Transported fishes are commonly subjected to a saltwater treatment to reduce disease and stress related to handling. We determined the toxicity of therapeutic salt treatments to veligers and juvenile zebra mussels as part of our study to develop a strategy for killing zebra mussels during fish transport.
Toxicity of Chloride Salts to Fishes and Zebra Mussels
A recommended therapeutic salt (NaCl) treatment for fishes is from 0.5 to 1.0% for an indefinite period-during hauling-or a 3% dip treatment for 10 to 30 min. Using this initial treatment guideline, we determined the toxicity of selected concentrations of the salts NaCl (1.0 and 2.0%), KCL (0.25, 0.5, and 1.0%), and CaCI2 (1.0 and 2.0%) to fishes and juvenile zebra mussels in 6, 12, and 24 hour exposures. Test fish (48 to 56 mm and 1.2 to 1.4 grams) included rainbow trout, channel catfish and bluegill. Juvenile zebra mussels measured 2 to 5 mm shell length. Following the exposure period, organisms were placed in untreated well water for 24 hours to monitor recovery or latent mortality. Latent mortality commonly occurred in both mussels and fishes and the final mortality was underestimated without the postexposure period.
The treatments that killed juvenile zebra mussels caused significant mortality in fishes. Exposures of 12 hours in the highest test concentrations were necessary to produce greater than 50% mortality of juvenile mussels. These exposure conditions, however, also produced from 13 to 100% mortality of fishes. A 24 hour exposure in the highest test concentration was needed to kill all juvenile zebra mussels in the treatment. Of the three salts tested, potassium chloride was the most toxic to the mussels; the percent mortalities of mussels in a 1% solution of salt during 12 (80%) and 24 hour (100%) exposures were high in KCL, compared with 0% in NaCl and 35 to 68% in CaCl2.
Therapeutic Levels Are Effective Against Early Life Stages of Zebra Mussels
Following tests with juvenile mussels and fishes, we tested the effectiveness of treatments that were safe to the three fish species against veliger and plantigrade mussels. Tests were conducted using the methods previously described, except that veligers were not held in clean water for 24 hours after exposure.
Several treatment schedules in these test conditions killed veliger and plantigrade stages of the zebra mussels. The mortality rate of veligers was 100% in several common NaCl treatments including 1% NaCl for 24 hours, 2% NaCl for 1 hour, and 3% for 15 minutes. In addition, all concentrations and exposures of KCL caused >90% mortality of veligers. Plantigrade mussels were less sensitive to the salts; however, 1% NaCl and CaCI2 for 24 hours and 0.25% KCL for 24 hours were effective against the mussels.
Control Options for Hatcheries Are Limited
Currently, there are no fishery chemicals approved for use in hatchery facilities against zebra mussels; yet, aquaculturists are immediately threatened with infestation of their facilities by zebra mussels or the unintentional dispersal of mussels into stocked lakes and streams. Chlorine has been the chemical of choice for control of zebra mussels in industrial settings-it is nonselective, however, and highly toxic to fish. Nonchemical methods of control (i.e., filtration, acoustics, and thermal shock) may be too expensive or impractical for general application.
Our results indicate that the NaCl treatments presently used in many hatcheries to reduce transport-related stress and disease will kill microscopic stages of the zebra mussel. Furthermore, several treatment levels of potassium chloride and calcium chloride were highly effective against early life stages. Higher treatment levels of calcium chloride and potassium chloride were also effective against larger zebra mussels but not without some risk to fishes. For example, a 2% CaCl2 treatment for 12 hours killed 100% of the juvenile zebra mussels but also caused 15% mortality of rainbow trout and 100% mortality of bluegill. Juvenile and adult mussels can also be removed by visual inspection of tanks and by filtering of the water supply.
Trap and Gill Nets
By: Steve Mortensen, Leech Lake Tribal Fish Hatchery
Steve Mortensen (Fish hatchery manager at the Leech Lake Reservation), provided MTAN with the following information regarding the making of fish collection nets. These devices work well for the capture of wild fish for broodstock or gametes. MTAN felt that because many Tribal hatchery managers are also involved with fishery management responsibilities, that they may benefit from this information. If you would like to have more details about the cost of these products, contact "Ojibwe Fish and Foods", RR 3 Box 100, Cass Lake, MN 56633, or call 218-335-6341
Trap Nets
Our trap nets are constructed with a solid steel framework, so they sink fast and are quick to set. The hoops are made from galvanized steel and the frames are formed from solid steel rod, welded and then painted with an enamel primer. Hoops are of a standard 30" diameter. Stock frames come in two sizes, 30" x 48" and 36" x 60". The inner winker frames come in 3", 6", or 12" widths. If you have the need for custom frames we can accommodate your needs.
Because of its lower abrasiveness to trapped fish, we stock a high-quality, knotless delta netting, in 1/4", 3/8"", 1/2", and 3/4" mesh. Standard dimensions for the small mesh is one throat at 4" diameter. The large mesh nets are double-throated, one at 8" and the other at 6" diameters. The throats and seams on the smaller mesh are sewn with a triple-stitch industrial surger. The larger ones are sewn by hand with #12 tarred seine twine. All ties on the outside framework are made with #18 tarred twine to give them extra durability.
Leads are a standard 4' deep by 40' or 50' long. They are tied in 4" spacings on 5/16" black twisted polypropylene at top and bottom. Float line has 2" x 1 1/2" PVC sponge floats every 2', and weight line has 1" lead balls every other tie. Float line and lead line are in stock and available on request.
Gill Nets
Our gill nets are made from your choice of top-quality multifilament or monofilament nylon gill netting. Our nets are made to stay limp, but deliver extra strength and durability. The mono nets, while not as flexible, are great in clear water.
All nets are tied tightly at the top line on #6 tubular braided polypropylene, with 1 1/4" x 5" hard plastic floats every 6', and on the bottom line we use 1/4" 30-lb. leadcore line. Lead inserts or lead balls are available on request. For hanging, #12 tarred nylon seine twine is used with an 8" tie spacing.
Multi-panel experimental nets are available on request. We carry, in the multifilament, 1/2" through 2", 2 3/4", and 3" mesh, and in the monofilament, 1 3/4", 2", and 2 3/4" mesh. Our standard gill net is 6" deep, but other depths are available. We also now offer 3' x 100' personal gill nets.
Seines and Holding Boxes
Our seines are made from the same top-quality, knotless delta mesh found in our trap nets, in 1/4", 3/8", 1/2", and 3/4" mesh sizes. We also stock 1/8" and 3/16" square mesh. Each seine is tied at the top on 5/16" black polypropylene, with 2" x 1 1/2" PVC sponge floats every foot. For the bottom we offer either a 9-strand mud line or a weighted line. All are tied every 4" with #12 tarred twine and are hung to bag properly.
Our holding boxes have triple-stitched seams sewn on our industrial surger, and are bordered at the top with black polypropylene with 2" galvanized rings tied at the corners. Floating boxes are available on request.
Larval Diet Studies In Rearing of Lake Sturgeon For Restoration
By: Martin N. Dilauro, William F. Krise, National Fishery Research and Development Laboratory, National Biological Survey, Wellsboro, PA. and Kofi Fynn-Aikins, Tunison Laboratory of Fish Nutrition, National Biological Survey, Cortland, NY.
A 60-day intensive culture experiment was conducted to ascertain diet-related differences in fish growth and survival in work supporting lake sturgeon restoration efforts. Lake sturgeon first-feeding fry were presented five different artificial diets which were fed in combination with brine shrimp (live food). These artificial dry diets were BioKyowa, Biodiet, Tunison, ASD, and SD-9. A sixth separate brine shrimp-only treatment represented the control. The fry were reared at 16.0 C + 0.7 C in 95 L tanks. Tanks were stocked with 9 fish per L and the fish were exposed to daily light equivalent to that of natural daylight for the date and region, with weekly adjustments. The BioKyowa/live food treatment fished to daily light equivalent to exhibited the highest survival (67.4%), while those in the SD-9/live food group produced the lowest survival (58.3%), however, these differences were not significant (P < 0.05). The live food treatment fish exhibited significantly greater mean length (60.4 m) with BioKyowa/live diet group indicating the lowest (44.2 mm). The mean weight of the live food treatment was significantly greater than all other treatments (0.74 g), while the Biodiet exhibited lowest mean weight (0.37g). Of the treatments tested, the live food treatment appears to be the diet of choice for first-feeding lake sturgeon.
Diet Preferences and Growth of Cultured Juvenile Lake Sturgeon
By: William F. Krise, Martin N. Dilauro, National Fishery Research and Development Laboratory, National Biological Survey, Wellsboro, PA. and Kofi Fynn-Aikins, Tunison Laboratory of Fish Nutrition, Cortland, NY. and Frederic T. Barrows, Bozeman Fish Technology Center, Bozeman MT.
Two 30-day studies, of method for conversion from brine shrimp to dry diet and diet preference of lake sturgeon 2 month old juveniles, were conducted to measure differences in diet effectiveness and fish survival. In the first study, lake sturgeon were weaned from brine shrimp to a dry diet by reducing the brine shrimp ration 60% over two weeks, then feeding only the dry diet. The dry diets tested were ASD salmon diet, SD9 trout diet, Biodiet, BioKyowa and a semi-purified diet. Fish kept on a control diet of 100% brine shrimp had the highest survival (98%), followed by those fed ASD salmon diet (69%), then those fed BioKyowa (62%), those fed SD9 (53%), semi-purified diet (49%), and Biodiet (44%). Fish fed ASD, brine shrimp or SD9 were largest (72-74 mm length), while fish fed other diets averaged 57-59 mm. Condition factor was lowest for fish fed brine shrimp (0.287), lower than those fed dry diets (0.300-0.350). Fish fed ASD and SD9 diets were heavier (1.28 and 1.25 g, respectively) than fish on other dry diets (0.66 to 0.72 g each). In the second study, fish previously fed only brine shrimp were converted directly to the diets listed above, plus sturgeon starter #9316. Survival was greatest for fish fed sturgeon starter #9316 (29%) followed by those fed BioKyowa (15%). Survival of fish fed other diets was < 10%, and included 0% survival in the semi-purified diet and SD9 fed groups. Fish fed the #9316 diet averaged 81 mm and 1.7 g, while those fed BioKyowa averaged 74 mm and 1.4 g. It appears that feeding brine shrimp to lake sturgeon enhances early survival and allows for a gradual weaning to dry diets. Benefits of the brine shrimp diet on growth are lost after about two months of feeding.
Selecting the Appropriate Geomembrane Can Enhance Breeding, Reduce Cost for Fish Hatcheries
By: Brian McKeown, GSI Geo-Synthetics, Inc., 428 N. Pewaukee Road Waukesha, WI 53188 1-800-444-5523
In the December 1993 issue of the MTAN, we promised our readers two additional perspectives regarding applications of plastic pond liners. MTAN hopes that the two articles which follow will not only help you better understand the different liners that are available, but also provide you with a source of different manufactures which produce and install this product.
In Wisconsin, lined fish hatchery ponds must be able to withstand a variety of conditions-frigid winter temperatures and accumulations of snow and ice; blistering summer heat and continuous exposure to damaging UV radiation, and different soil and sub-grade characteristics. At the same time, hatchery operators are looking for products that can enhance breeding and simplify maintenance.
Many hatchery operators are using geomembranes as containment liners for their ponds. Geomembranes can withstand abusive climatic conditions and eliminate problems with mud bottoms resulting in better breeding conditions. There are several basic liner materials that offer various advantages for fish hatcheries. It is extremely important to use materials that will meet your specific site characteristics. For a fish hatchery in northern Wisconsin, selecting a more suitable liner material saved the Fish and Wildlife Department more than $100,000. Knowing the features and advantages of the different geomembranes can help you make the right choice. Following are descriptions of various liner materials offered in industrial and fish-grades.
Polyvinyl Chloride (PVC)-is a highly flexible membrane that withstands uneven surface contours and shifting of subgrades. These qualities minimize leakage potential, which is why PVC is used as a containment liner. The material works well under frigid or sub-tropical temperatures, and is available in standard grade and UV-stabilized material. It comes in thicknesses from 10 to 60 mm.
High Density Polyethylene (HDPE)-is specified for hazardous waste landfills and other applications where the liner comes into contact with various chemicals. This liner material offers excellent tensile strength and resistance to tears. it is also highly resistant to the damaging effects of UV radiation. It is available in thicknesses from 40 to 100 mm.
Very low Density Polyethylene (VLDPE)-is flexible and used in situations where the membrane must conform to varying ground contours or shifting and settling subgrades. The material has good resistance to punctures and stresses, but does not have the overall tensile strength of HDPE and is not recommended for exposed applications. It is available in thicknesses from 40 to 100 mm.
Coex Seal-is a relatively new product, having been on the market for only a few years. Coex Seal is a coextruded geomembrane containing VLDPE layered between HDPE. The VLDPE provides 60% of total composition and each HDPE layer is about 20% of the total thickness. This liner combines the most desirable properties of HDPE and VLDPE, to offer optimum strength, flexibility and resistance to UV. It is available in 40, 60, 80 or 100 mm thicknesses.
Fish Hatchery Case Stud
The Wisconsin Department of Natural Resources needed to construct seven new ponds and re-line five existing ponds at a fish hatchery in northern Wisconsin. The liner would be exposed to sunlight and needed a life expectancy of 20 years.
Originally, 650,000 square feet of VLDPE liner was specified in the bid for the project. Previous tests on VLDPE showed that it would not provide adequate durability, and UV resistance; the needed characteristics for this application. Working with the general contractor, GSI requested the opportunity to modify the specification. Based on the characteristics, we felt Coex Seal, (manufactured by National Seal Corporation), would be the optimum choice for the job because of its flexibility and resistance to UV rays.
Switching to the Coex Seal geomembrane also reduced the liner costs significantly as more than $100,000 was saved on the project. In addition to providing the liner, GSI installed and field welded the liner panels. With Coex Seal, the VLDPE core offers added flexibility for greater contact with the soil, while the HDPE exterior provides the UV resistance. This makes the installation more efficient and economical.
GSI also conducted performance and quality control testing throughout the project. The seams must be as strong as, if not stronger than, the liner material, to withstand the stress of water pressure, shifts in the soil and other conditions. We test every inch of the seams to help ensure that there are no leaks.
To date, seven of the twelve fish hatchery ponds have been completed. The last five will be lined in the spring of 1994.
Coex Seal has been used in a variety of applications, but this was the first time it was used to line fish breeding ponds. We think you'll see Coex Seal being used more and more for fish hatcheries because it has durability to withstand the elements, flexibility, for ease of installation, and could even reduce overall liner costs.
Flexible Membrane Liners for Fish Hatcheries
By: Janice Hall, Technical Services Manager, JPS Elastomerics Corp. Environmental Products Division, Northampton, MA 01060, 1-413-586-8750
The days of traditional aquaculture have almost faded completely: when fish hatcheries were comprised of earthen ponds; when facility operators labored over drying and reshaping ponds after cleaning them; and when 30 to 35 percent yields were considered good.
The industry is in the midst of a revolutionary change that will take hatcheries into the 21st century. The change, driven by the simple installation of liners on pond basins, is environmentally friendly, makes good economic sense, and is easy to install.
Geomembrane Lining Systems
The two most commonly specified lining systems utilize geomembranes based on two different--and each in their own right, highly successful--polymers: DuPont's Hypalon7 cholorosulfonated polyethylene (CSPE or CSM), and Himont Advanced Polymers' Polypropylene.
The largest and most recent JPS aquaculture installation is the Dundee Fish Hatchery in Wichita Falls, Texas, and is the largest in the state. The Texas Parks & Wildlife Department specified flexible liners on 73 of Dundee's 99 warm-water ponds totaling 59.5 acres. This was undertaken with the objective of combating bacterial contamination, to which unlined ponds are very susceptible. Bacteria can emanate from the basin of an earthen pond and combine with existing bacteria in the water, creating a greater risk of disease and a correspondingly lower fish yield.
Testing had shown that ponds with liners have less bacterial build-up from uneaten food and fish waste because they are easier to clean and maintain. The healthy growth and development of fingerlings is dependent upon a clean environment which will ultimately result in a higher yield. The high pressure hoses used to clean a pond work best on the smoother surface of a synthetic liner, thus providing the cleanest environment possible in the least amount of time. A liner system also helps the pond maintain its shape by reducing silting and erosion problems.
Geomembrane Construction & Properties
JPS Aquaculture Liners are typically reinforced with a 10 x 10, 1000 denier polyester scrim for increased tear and puncture resistance. At the same time, they are flexible enough to easily conform to irregularities in the pond basins. Both Hypalon and Polypropylene-based liners are NSF-61 approved. The JPS Polypropylene Liner has the added advantage of having a somewhat rougher surface than other geomembranes, providing better footing for workers when they clean the drained ponds with high pressure hoses.
The membrane is manufactured in 76.5-inch rolls, which are then prefabricated into large panels of up to 100 x 250 feet in size. These factory seams are made using a variety of dielectric, thermal, or chemical fusion seaming methods, depending on the fabricator. The large panels are then shipped to the pond site, where they are stretched out and final field seams made to create the finished liner. Hypalon-based geomembranes are field seamed using a chemical fusion method. Polypropylene liners can be field seamed using thermal welders (wedge or hot-air). The membrane is typically anchored around the perimeter using a berm at the top of the side slopes.
Both Hypalon and Polypropylene membrane liners have excellent coefficient of expansion and contraction, so they lay flat after installation preventing fish loss in folds and wrinkles. In addition, liners made from these two polymeric materials will not stress crack.
Once the pond is lined, the membrane may be covered with earth or left exposed. Hypalon and Polypropylene liners exhibit outstanding resistance to ultraviolet radiation and harsh weather, making them ideal for exposed applications. In aquaculture applications, leaving the membrane exposed makes cleaning much easier.
Flexible Membrane Liners and the Future
The future of fish farming was highlighted in the industry publication, World Aquaculture, when it cited an average annual increase of 13.6 percent from 1984 to 1990, and an additional increase of 5 percent per year expected through the year 2000. Production is anticipated to be 20 million tons by that time. These figures are evidence of the continuing need to educate hatchery operators to the production economies of this relatively new technology to the growing aquaculture industry, namely flexible membrane lining systems. {A note from the MTAN} A listing of successful JPS liner installations is available through JPS or the MTAN.
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Product and company names mentioned in this publication are for informational purposes only. It does not imply endorsement by the MTAN or the U.S. Government. |
