Extensive Walleye Production UWSP NADF Pond Culture 2017 Prepared By: Emma Wiermaa, Facility Outreach Specialist Greg Fischer, Facility Manager Kendall Holmes, Facility Foreman Introduction: Due to a collaboration with Red Cliff Tribal Hatchery, the University of Wisconsin- Stevens Point Northern Aquaculture Demonstration Facility (UWSP NADF) provided approximately 50,000 small fingerling walleyes (~45mm) for stocking in inland Wisconsin lakes. These walleye were raised in two outdoor rearing ponds at the UWSP NADF and were stocked by Red Cliff Tribal Hatchery staff. The information presented in this case study describes the methods and techniques used by UWSP NADF to incubate and pond raise walleyes to small fingerling size. The UWSP NADF used two outdoor earthen ponds, each 0.4 acre (0.16 ha) in size, utilizing both organic and inorganic fertilizers, various aeration systems and an external collection kettle for harvesting. In June of 2017, two ponds were harvested which totaled around 50,000 small fingerling walleye, averaging about 81% success in Pond 1 and 50% success in Pond 2 from fry to small fingerling. The intent of this report is to provide information to assist other aquaculture personnel that are raising walleye or similar species. These techniques have been formulated for UWSP NADF ponds and may differ for other hatcheries or facilities. These protocols can be used as a starting point for pond culture but may need to be adjusted for specific farm sites. Methods: Chicken Waterer Head Tank Trough Insert Tanks Fiberglass Tanks Figure 1. McDonald style bell jar incubation system at UWSP NADF. A chicken waterer was used to drip formalin treatment into incubation system head tank. As fry hatch from the jars they flow with the water into the trough and through piping to designated fry insert tanks.
Eggs: Eggs were collected and fertilized lake side by Red Cliff Hatchery staff from two locations (Lake Owen and Lake Namakagon). No information regarding egg fertilization or transportation was provided. The water hardened eggs were disinfected with 100 ppm iodine in a 10 minute bath and transported to UWSP NADF where they were tempered and placed in a bell jar incubation system located at the facility (Figure 1). Fertilization success was calculated for each group of eggs (Figure 2). Lake Namakagon Eggs: Approximately 2.0 liters of eggs were placed in McDonald style egg jars on April 18 th. Egg fertilization was determined at an average of 44% success, utilizing CellSens software at about 10X microscopic power. Fry began hatching on May 3 th and finished on May 15 th. Lake Owen Eggs: Approximately 1.0 liters of eggs were placed in McDonald style bell jars on April 24 th.egg fertilization was determined at an average of 43% success, utilizing CellSens software at about 10X microscopic power. Fry began hatching on May 7 th and finished on May 17 th. A. B. Figure 2. CellSens software was used to determine fertilization success. Photo A: Comparison of a fertilized egg (left) from an unfertilized egg (right). Photo B: One snapshot of a random sample of eggs at around 10X. Fertilization success was determined by taking the average success observed in three random snapshots of a group of eggs. Incubation: Temperature was maintained at 7.8-10ºC throughout incubation and increased to 15ºC during hatch-out to aid in hatching. Initial water flow through the jars was approximately 1.0 liter per minute then increased to 4.0 liters per minute once eggs became eyed. Dead eggs were siphoned out and
removed every other day from the hatching jars. To control fungus, eggs were treated daily with a 15 minute formalin drip (1600 mg/l). A modified chicken waterer was used to disperse treatment into the bell jar head tank over the course of 15 minutes. Formalin treatments were discontinued near egg hatch-out A. B. Figure 3. Fry insert tanks to collect 3-5 day old sac fry. Photo A: A box screen is utilized to enhance water drainage from the tank. Aeration tubing runs along the bottom of the box screen to provide a bubble curtain, keeping the screen clean of egg shells and fry mortalities. Photo B: Strong swimming fry are attracted to a light source, here they are concentrated to be obtained for stocking the ponds. Initial Pond Stocking: After hatch out, 3-5 day old strong swimming fry were collected from the incubation system insert tanks using a light source (Figure 3). They were then counted utilizing a JenSorter Larval Counter and stocked into the ponds. Pond 1 was stocked with 30,000 fry on May 15 th and 11,000 fry on May 17 th. Fry were carefully tempered from 12.1ºC to 14.6ºC at pond side before they were stocked. Pond 2 was stocked with 30,000 sac fry on May 16 th. Fry were tempered from 12.1ºC tank temperature to 13.5ºC pond water temperature. Pond Fertilization: Fertilization amount and timing is crucial to the survival of the walleye. With fertilizer application, nutrients are released which create phytoplankton blooms within the ponds, thus creating various zooplankton populations. During the first month of pond rearing, walleye consume various groups of zooplankton, beginning with rotifers as an initial first food source. It is important to match the timing of small rotifer population blooms with the hatching and stocking of young fry. As fish grow, they begin feeding on larger zooplankton such as copepods and then to cladocerans (also known as daphnia). Zooplankton population trends in ponds start with fast growing and multiplying rotifers and proceeds to cladocerans after several weeks and then to copepod populations after 3-4 weeks. Although copepods are the next food source for young fry after rotifers, copepod populations may take a month to develop within a pond. This is why proper timing is important to remember when managing food sources for your fry. Zooplankton levels should be monitored and managed regularly to ensure appropriate population levels and species in your pond environment (see figure 4).
Figure 4. Various zooplankton as initial food source for young walleye fry to small fingerling. From left to right; rotifer, copepod and daphnia. Walleyes will consume rotifers first, then feed on copepods and then to daphnia as the fish grow. There are two general types of fertilizers used to enhance pond productivity, organic and inorganic. Fertilizers considered organic generally include composted plant material or manure that contain high amounts of nitrogen and organic carbon. These fertilizers slowly release nutrients over a period of time which are utilized by phytoplankton. Inorganic fertilizers, in comparison, are man-made chemical solutions or pellets specifically containing precise elements utilized by autotrophic food chain which is driven by sunlight. Inorganics provide an immediate influx of nutrients to a pond system. UWSP NADF utilizes both organic and inorganic fertilizers. There are a variety of fertilizer products available based on accessibility and cost at the local feed mill. Alfalfa meal is generally used as an organic fertilizer at UWSP NADF. Ammonium sulfate (Nitrogen source at 21-0-0) and granulated phosphorus (at 0-45-0) are available as inorganic fertilizers. Urea has also been used as an inorganic fertilizer in UWSP NADF ponds (Nitrogen source of 46-0-0) but was no longer available locally. Generally, UWSP NADF follows a fertilization schedule that was created for the facility s clay lined half acre ponds based on previous years success (Table 1). Fertilization amount and timing may vary each year and depends on a variety of factors including weather, temperature, plankton numbers, water clarity or turbidity, and initial stocking density. For initial fertilization, 400lbs of alfalfa was added to each pond and was distributed across the bottom before water was added on April 25 th. Water was slowly added to the ponds following initial organic fertilization. On April 28 th, both ponds were fertilized with inorganics; 11 pounds of urea (leftover from previous year) and 1 pound of phosphorus. Standard fertilization was applied throughout the rearing period, generally following the basic schedule (Table 1).
UWSP-NADF POND FERTILIZATION SCHEDULE Initial fertilization (approx. April 20, depending on weather) 400 pds Alfalfa meal or Soybean meal 18 lbs/1.7 gal liquid Urea (28-0-0 nitrogen) 1.0 lb phosphate(0-45-0 liquified) Spread organic fertilizer before filling, spray liquid inorganic fertilizer into water Standard fertilization (approx. every week or as needed)(verify with seechi disk readings and plankton sample tows). 100 lbs alfalfa meal or soybean meal 3.0 lbs Urea 0.5 lbs phosphate applied through June, as long as plankton bloom is needed Table 1. UWSP NADF general pond fertilization schedule for half acre clay lined ponds. Pond Aeration: A 5 horse power main rotary air blower system to provide aeration to all ponds through in-pond rubber diffusers. A Kasco surface aerator was used for emergencies when oxygen dropped to dangerous levels below 4ppm. Screening had to be wrapped around the aerators to protect the young fry from the prop. Fresh well water, which is degassed and aerated, was also added at 8 C periodically to also assist oxygen levels and temperature control, during the rearing season as well as during harvest. Fertilization Costs: Local Agriculture stores in various locations may vary on pricing. UWSP NADF purchased alfalfa meal at $16.95 per 50 pounds, phosphorus fertilizer at $0.36/pound, nitrogen-urea $1.56/pound, and ammonium sulfate at $1.40/pound. Total cost of fertilizer for both ponds during the rearing period was $631.57. Pond 1: A total of 800 pounds of alfalfa meal costing $271.20, 2.75 pounds of phosphorus costing $0.99, 11 pounds of nitrogen urea costing $17.16, and 26 pounds of Ammonium Sulfate costing $36.40. Total fertilizer cost for Pond 1: $325.75. Pond 2: A total of 750 pounds of alfalfa meal costing $254.25, 2.25 pounds of phosphorus costing $0.81, 11 pounds of nitrogen urea costing $17.16, and 24 pounds of ammonium sulfate costing $33.60. Total fertilizer cost for Pond 2 was $305.82.
( C) (ppm) University of Wisconsin-Stevens Point Optimal Temp (23 C) Min. Oxygen (5ppm) Graph 1. Pond 1 temperature in red (left y-axis) and oxygen in blue (right y-axis) throughout the rearing period graphed every two days of monitoring. Temperature and oxygen was monitored every morning near the pond apron. Graph also shows weather throughout the rearing period; sunny, partly cloudy, cloudy or rainy on the x-axis above the date monitored. The dotted red line shows the optimum temperature for best walleye growth at 23 C, the dotted blue line shows the minimum oxygen requirement for best fish performance (growth and survival). Pond Monitoring: Every morning ponds were monitored for temperature and oxygen along with recording weather each day (Graph 1). Water turbidity was checked nearly every day using a secchi disk, managing the pond to at least a reading of 12 or less, meaning at 12 the secchi disk should no longer be visible. Pond ph was monitored every few weeks to ensure safe levels between 6-9pH. Fish were sub-sampled weekly to assess length, weight, and overall fish condition such as fin condition and body proportions (Figure 5). Pond zooplankton levels were checked every week using plankton net and microscope at 1X power to determine plankton species and population in the pond (see Figure 6). cm Figure 5. Pond reared fingerling walleye at 30 days post hatch averaging around 30mm. These fish show good fin quality, and body proportions. Gut is plump and head looks proportionate to rest of body.
Figure 6. Sample of zooplankton populations under a microscope at around 10X using a plankton net of three tows in Pond 1 on May 16 th. This shows a good amount of zooplankton of varying sizes and species. Rotifers, daphnia and copepods are present in this sample. Figure 7. Concrete funnel shown in an empty or drained pond (left) and in a filled pond (right). Pond bottom is slightly sloped towards the middle and down to the funnel to drain the fish with the pond water which then gravity feeds into a collection kettle for harvest.
Harvest Techniques: Several days before final harvest, the water from each pond is slowly drained via gravity into an external harvest kettle by use of gate valves and dam boards located in the concrete funnel structure at the rear of the ponds (Figure 7). A vinyl swimming pool 12 diameter by 3 deep is set up alongside the kettle for excess fish during harvest. Aeration and freshwater is provided to the harvest kettle and pool during draining. The pond is drained down to approximately half before the final harvest day. Most of the walleyes stay in the last half to quarter of the water left in the pond. Harvest day is planned around the weather and the health of the fish. Weather should be cool and cloudy for harvest and should happen in the early morning. Fish should look plump and healthy for best survival (Figure 5). The fish were netted from the kettle, weighed in water, and transferred to Red Cliff Hatchery Hauling truck which was parked next to the kettle (Figure 8 & Figure 9). The fish were then stocked into inland lakes by Red Cliff Tribal Hatchery as part of Red Cliff s walleye conservation program. Figure 8. Walleye fingerlings from each pond were harvested from the kettle and weighed in a bucket of water before transferring to the hauling truck. Figure 9. UWSP NADF staff harvesting fingerlings from the collection kettle and weighing the fish in water (left). Buckets of fish were handed to Red Cliff Hatchery staff to place into the hauling tanks (right).
Results: Fish were harvested in the morning on a cool, rainy day on June 28 th. From Pond 1, 33,288 fish were harvested, which resulted in about 81% survival of initial stocked fry. From Pond 2, 14,891 fish were harvested, resulting in about 50% survival of initial stocked fry. Pond 1 fish averaged 1250 fish/kg (average weight:.80gm, average length: 48 mm). Pond 2 fish averaged 1174 fish/kg (average weight:.85gm, average length 47 mm), see Table 2. Pond (%) Egg Fertilization Success Initial Fry Stocked Ave. Fish Length Ave. Fish Weight #Fish/Kilogram Total Fish Weight Harvested Total #Fish Fry to Fingerling Success (%) Pond 1 43-44% 41,000 fry 48mm.80 gm 1250 f/kg 26.63 Kg 33,288 fish 81% Pond 2 43-44% 30,000 fry 47mm.85 gm 1176 f/kg 12.66 Kg 14,891 fish 50% Table 2. Average success and fish samples from Pond 1 and Pond 2. N=50 from each pond. Discussion: Temperature and oxygen posed an issue for starting and managing ponds this year. Snow and sleet was recorded during the first week of initial fertilization on April 25 th and less than optimal sunny days were recorded during the rearing period. 60 days were recorded for weather conditions during the rearing period, with just over half of those days (35) recorded as sunny or partly sunny. The other days were rainy, cloudy or overcast. Not enough sunlight lead to low intitial plankton blooms, low oxygen levels and low pond temperature. Fortunately, low oxygen levels in the pond was managed by use of diffusers, Kasco aerators, and addition of fresh water. Unfortunately, pond temperature remained below the optimal for walleye production, which is 23 C, according to The Walleye Culture Manual (Summerfelt, et.al.). This optimum temperature was never recorded for Pond 1 or Pond 2 during the rearing period. Although ponds may have reached this temperature during the afternoon, maximum morning temperatures were recorded at 22.7 C and 22.5 C for Pond 1 and Pond 2, respectively. Non fish species such as tadpoles and clam shrimp were unable to be separated from the walleye fingerlings in the kettle, in Pond 2. Final weights were then adjusted to account for the added weight of these species. Acknowledgements: This project was a collaboration between UWSP NADF and Red Cliff Tribal Hatchery, to support the tribe in walleye conservation efforts. Red Cliff Tribal Hatchery provided the fertilized walleye eggs and organic fertilizer, assisted with harvesting as well as transported and stocked the walleye into inland lakes. Also, special thanks to UWSP NADF Technicians Jared Neibauer & Jim Miazga, UWSP NADF intern Josh Siebert and Michigan State Doctoral Candidate Tyler Firkus.
References: R. C. Summerfelt, Walleye Culture Manual, in Walleye Culture Manual, 1996. Download available at North Central Regional Aquaculture Center: https://www.ncrac.org/content/walleye-culture-manual Four half acre, clay lined and drainable rearing ponds at UWSP NADF.