Study to Reduce Parasitic Infestations of Yellow Perch in Flow-Through Outdoor Growout Systems

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2008: $6,000.00
Projected End Date: 12/31/2010
Region: North Central
State: Wisconsin
Project Coordinator:
William West
Blue Iris Fish Farm

Annual Reports


  • Animals: fish


  • Animal Production: parasite control, preventive practices
  • Education and Training: on-farm/ranch research
  • Pest Management: physical control, prevention


    Blue Iris Fish Farm, LLC raises fish in nine ponds covering approximately six acres of a forty acre parcel. The farm is self contained and we guard against the run-on of contaminants such as pesticides, herbicides and fertilizers. The main pond (approximately 3 acres) contains water which is derived 100% from snow melt and rainfall. Blue Iris manages the complete life cycle of yellow perch from managing adult brood stock to spawning to growout. Within that cycle Blue Iris captures and hatches eggs, develops feed trained fingerlings, and manages a two-year growout of adult fish for the food market.

    While we have the use of six acres of water, we try to raise more and more fish using less and less water. We conduct research annually on reducing the footprint of our operation and grow more quality fish with less water. This grant was a step in assisting with the steps necessary to accomplish that goal. Our ponds are generally home to several unwanted species of fish. We have been able to harvest one species and make a smoked fish product for a profit. Other fish species can be used for fertilizer as can harvested algae and aquatic plants.


    The goal was to produce a high quality fish outdoors by reducing or eliminating parasitic infestations. Yellow grub and black spot are two parasites that infest a host of economically important fish species. There are few if any proven economical means to raise fish in outdoor ponds without encountering parasite infestations. Typical control mechanisms include biological control (e.g. Asian carp), chemical control (copper sulfate), and physical (draining ponds). All of these methods interfere with production. By using a flow-through system, this study was able to show that no infestations occurred while at the same time production was increased and fish quality was greatly enhanced.

    Parasites which infest fish for the most part come from infected snails. The infective stage of the parasite is a slightly mobile larva which attaches to a fish when the fish swims in contact with the parasite. The premise of the study was to assume that a slightly mobile parasite would not be able to infect a fish in a moving water body. Since indoor recirculating aquaculture systems (RAS) are already known to be capable of raising many different species and these systems are moving water environments, it seemed logical that an outdoor setup of an RAS system might discourage parasitic infestations. This may be true even if the pond water used to feed pond-side tanks is known to be infested with parasites.

    To test this theory, four pond-side tanks were set up and one net pen was placed in the pond. The net pen was similarly stocked with fish but used as a control. Water was pumped continuously through the tanks and returned to the pond. Fish were fed using belt feeders. The study continued for approximately three months (June – August 2009). The study was terminated when low water levels due to drought reduced water quality sufficient to apply too much stress on the fish.

    During the test period, necropsies were conducted on approximately 360 of the 3000 fish used for the study. There were no parasitic infections in any of the fish. While this was only one test, it is believed that similar results might be achievable in other flow-through systems such as floating raceways.

    Blue Iris Fish Farm enlisted the assistance of the University of Wisconsin Stevens Point, Drs. Chris Hartleb (fisheries biologist) and Todd Huspeni (parasitologist) and UW Stevens Point interns to provide oversight and perform necropsies on fish.

    The study was set up to test a theory that fish in moving water might not become infected with parasites as readily as their counterparts in quiescent pond water. Because the blue heron is the host for the adult of the yellow grub parasite and the snail is the intermediate host, water used in the study was taken directly from an infected portion of the pond. None of the fish used in the study were observed to become infected.

    During the 2009 study window, Blue Iris conducted a secondary study on parasitic infestations. In the second study, Blue Iris captured 250 yellow perch fingerlings over a two month period (October 2009 to November 2009). These fish were from the same pond and the same water as which fed the tanks of the primary study. Of the 250 fish tested, only one fish did not have parasites. Infections observed in the fish ranged in number from two to over twenty per fish. This secondary test proves that there is a healthy infestation of parasites in the pond, that fish do acquire the parasite in a very short time window (noticeable infections within three to four months), and, even with the parasitic load present, fish subjected to the infestation in the moving water did not become infected.

    The primary study was not designed to optimize all parameters. For instance, the pond-side tanks were not stocked to maximum density (600 fish were stocked per 900 gallons of water). Optimum density for indoor systems is about two fish per gallon. The reason for stocking at a lower density was because to obtain water known to be infected, the source water had to come from a shallow bay which was weedy (good snail populations) and could be subject to summer heat. Therefore the water source was considered to be of lower water quality than preferred. Because of that, stocking densities were lower.

    As with any automated system, there needs to be an oxygen backup system. Blue Iris debated about the type of system to install and evaluated three options. The options included: one, backup based on power outage; two, backup based on pump failure without power outage; and three, backup based on low oxygen when power remains on but pumping is insufficient due to intake obstruction. During the study, Blue Iris never experienced electrical outage or pump failure but pump blockage and insufficient water supply did end up lowering oxygen supply to the tanks. In addition, a prolonged drought lowered water levels in the area of the intake compounding the problem with oxygen supply. Blue Iris believes that oxygen backup should be based on oxygen needs of the fish regardless of pump failure. Therefore, a high/low level oxygen sensor with standby oxygen source should be part of the water quality scheme.

    Blue Iris observed after the first month of the study that the fish in the net pen in the pond (control) were growing faster than those in the pond-side tanks. It is believed that the flow provided in the tanks was too fast and that the fish were using up the energy of the food to maintain position in the tank. It is known that the fish feed for yellow perch results in fat deposition in the body cavity unless the fish are in moving water. Therefore some differences in fish size from tank to net pen were anticipated. Usually these differences are made up in fillet yield where tanked fish seem to convert more feed to protein. Unfortunately, the fish in this study were not market size by September to observe differences in fillet yield.

    As noted above, none of the fish were observed to have parasites by the end of the test window. Based on the results of the necropsies, it is believed that this culture technique will be a method for preventing parasitism in fish even if the water source is infected with parasites.

    To initiate the study, Blue Iris purchased fish which were between three and one half to four inches and parasite free. Necropsies were conducted at the beginning of the study and at monthly intervals. It is possible that fish in the later part of the study (August) might have become infected even though no parasites were observed. The purpose of enlisting the assistance of the University of Wisconsin Stevens Point (parasite evaluation) was to identify infections that might be newly encysted near the end of the study which might otherwise not be noted through cursory observation. However, even with this level of inspection, no parasites were observed.

    There are many farmers who raise fish in outdoor ponds. Outdoor aquaculture is much less capital intensive than raising fish indoors however, production outdoors is substantially less per unit of farmed water and the quality of fish and fillet yields are lower outdoors. Many species of fish are susceptible to various parasites when raised outdoors and if parasitism is left unchecked, entire crops of fish can be unsuitable for use in the fish food market.

    The results of this study indicates that it is possible to raise fish using outdoor pond water (even if it is infested with parasites) without having the fish become infected with parasites. This was accomplished by using pond-side tanks and recirculating pond water through the tanks which housed the fish.

    Demonstrating that fish may not take up parasites given this scenario is one problem addressed by this study. Looking at the big picture, we want to be able to raise significantly more fish in pond-side tanks (or other moving water situations such as floating raceways) and in so doing, approach indoor production numbers. As noted above, the two parameters which appear to be limiting in this study were one, the ability to provide high quality feed water and two, the lack of a reliable oxygen backup system.

    Over the past eight years Blue Iris has spawned millions of perch. At any given time, there are thousands of fish that inhabit the water and most have at least a mild infection of parasites. Each year an attempt is made to bring at least a thousand fish to market to sell as food fish. To do that requires labor to pull nets, weed harvesting, sizing and grading equipment etc. With all that, we still end up with fish that are a wide range in size, many with at least some parasites, and by and large running smaller by way of fillet yield than indoor raised counterparts. This year with the installation of the pond-side tanks, we spend a little bit more time monitoring on a daily basis but when harvest time comes, it takes about 10 minutes to drain a tank. Since you could easily have 1000 fish in one tank, one tank exceeds the typical harvest from the entire three acre pond. The overall cost savings and production potential per unit effort is substantial. The reason pond-side tanks work well is because of the following:

    1. You know how many fish you have per tank
    2. You know how much feed it is going to take to feed the fish
    3. You can monitor the fish daily for health and well being
    4. You can protect the fish from parasites and predation
    5. You do not need much water (we can raise many times more fish with less water by not putting the fish in the pond)
    6. Labor associated with harvesting is negligible compared to traditional pond harvesting.

    Item #5 above has not been discussed much but it is the most important. As indicated before, there are many thousands of ponds in which fish are raised and this represents thousands and thousands of acres of water in the United States. What we know is that if we do not put the fish in the pond but in pond-side tanks, we can raise many times more fish. What this means is that a fish farmer can be successful with very little water – there is no need for expansive acres of water. This opens the door for farmers to raise fish successfully on very small farms.

    The primary focus of this study was to study methods to reduce or eliminate parasitic infestations of fish. The economic losses to the fish industry from yellow grub are in the billions annually. These losses are related to very important farmed species such as catfish, hybrid striped bass, yellow perch and bluegill (sunfish). Many species tolerate high density production methods and several tolerate flow-through production systems. This study demonstrated that yellow perch could be raised in a flow-through production setting without becoming infected with parasites even though the parasites were present in the water.

    If the results of this study can be applied to other similarly infected species, the economic impact would be immeasurable. There is a small trade-off with automating fish production outdoors (electric, tanks, etc), however, that is more than offset by having 100% of the fish harvested from the tanks parasite free. Economies for raising perch are as follows:

    1. Tens of thousands of perch can be raised with only ¼ acre of water. Alternatively, a well developed 40 acre perch operation will cost over $500,000 to purchase and develop (purchase of land, construction of ponds, utilities, buildings, etc).
    2. Using flow through systems, water usage is at a minimum (recycled). There is no need for large expanses of water for ponds which need to be permitted as would a high capacity well (if required).
    3. Labor is reduced to less than a full time equivalent for most daily activities.
    4. No requirements for pond maintenance, weed harvesting, seining, fish harvesting and all associated equipment, equipment storage requirements.

    This project is one phase of a larger concept – sustainable aquaculture. By solving the problem with parasites, production can move forward into more intense aquaculture production. This can be done in a smaller and smaller footprint. In doing so, production uses less and less water but cleans and reuses the water it does use. Waste from the water and the water itself is used for fertilizer, aquaponics, and other reuse ventures such as vermiculture. Therefore, we have gone from an economically driven project to one that has significant environmental and social impacts.

    As part of this project, Blue Iris Fish Farm, LLC has conducted two field days in 2009. At least two more are planned for 2010.

    In 2009 Blue Iris hosted the aquaculture class of UW-Stevens Point, Stevens Point, WI. A total of 15 individuals toured the facilities of Blue Iris and were given three hours of talks regarding aquaculture. Similarly, Blue Iris hosted a tour from West DePere High School where 10 students toured the facility.

    In November 2009, Blue Iris presented a summary of the project at the National Small Farm Trade Show and Conference in Columbia, MO. Approximately 6-10 people attended the specific presentation and a similar number visited a booth after the presentation.

    Blue Iris is preparing a power point presentation for the Wisconsin Aquaculture Association annual convention. This presentation will be given in March 2010 and is anticipated to have an audience of between 100 – 150.

    Blue Iris has contacted the State of Wisconsin and has received additional interest in expanding the project whereby farm-scale operations can be evaluated. Similarly, in collaboration with the University of Wisconsin, Stevens Point, Blue Iris is presenting its research to a wider body of aquaculturists (North Central Regional Aquaculture Center – NCRAC) to move the information into a twelve state arena.

    In the past Blue Iris has individually hosted one day seminars to provide training to small farmers. Blue Iris intends to host one or more seminars in 2010 specifically devoted to providing information obtained from the project.

    It is very refreshing as a small farm entity to be able to apply for and obtain a grant under the SARE program. Obviously, funding is very limited and a project has to be very well thought out to make the best use of the available funds and, more importantly, result in something that is really worth while to the end user.

    I have several ideas as to how to achieve outreach but I think that the program ought to have a repository for final reports. This project certainly will need a final report (which is being prepared) but it would be nice to have the SARE Program take credit for good projects.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.