Dedicated To The Tribal Aquaculture Program

March 2003-Volume 43

Topics Of Interest:

AquaMats

Pond Fertilizing Procedure Used At The Lac du Flambeau Indian Reservation

Pond Fertilizing Procedure Used At The St. Croix Indian Reservation

Pond Fertilizing Procedure Used At The Leech Lake Indian Reservation

Fertilization Procedures for Pond Culture

Pond Management Tips

AquaMats
By:  Jamie Ennis, Meridian Aquatic Technology, LLC, 301-937-1240

... "By combining the natural habitat, food production, and biofiltration functions of natural seagrass beds and coral reefs, the developers of AquaMats are revolutionizing aquaculture by bringing these natural environmental conditions into the commercial rearing of fish and other aquatic animals and showing remarkable successes in doing so. "

By definition, aquaculture is the reproduction and manipulation of an aquatic environment in order that it may sufficiently support a given species.   The idea seems simple enough; give those slippery little babies water to swim in, food to eat and a fair ratio of girls to boys and poof youve got aquaculture, right?  Well, commercial production of aquatic animals either for consumption or restocking programs is infinitely more complicated than a dictionary could ever attempt to describe.  Mutating diseases, carrying capacities, food conversion ratios, biosecurity, and genetic diversity all sound like Sci-Fi titles but are very much a part of everyday operation of todays aquaculture facilities.   And as with most things in the 21st century, technology has been there to answer the call when problems arise.  Ozone for all the creepy crawlies you cant see, water quality monitors that will page you at the bowling alley should your pH drop, not to mention 47,975 types of equipment to make sure the dissolved oxygen is just right; all there at the touch of a button for your convenience.  However, for all its advances, technology has yet to eliminate the presence of disease or discover the perfect diet or for that matter be able to keep up with half the problems our fish seem to come up with everyday.  But maybe thats the point.  Maybe, just maybe, a patchwork of solutions isnt the way around these problems.  

Perhaps there are lessons we can learn from nature that could be applied in a modern aquaculture faculty to produce a more self-sustaining environment rather than one that needs constant maintenance.   Perhaps we can learn to stop banging our heads against the wall rather than taking aspirin for the pain. 

Natural Rearing

Natural Rearing is a method of looking at an animals natural habitat and attempting to reproduce that environment as best as you can in order to make that animal happier and ultimately healthier.  Why in the world should Joe Fishfarmer care about his fish being happy?  Because a happy fish grows faster, grows bigger, has superior Food Conversion Ratios (FCRs), is considerably less susceptible to disease and will never know what an eroded dorsal fin feels like.  Make a list of the things that fish have access to in the wild and youll see there is a lot more on that list than clean water and pellet food. 

In aquaculture, the most common application of Natural Rearing is installing structure or habitat of some sort in the ponds and rearing tanks.   Everything from Christmas trees to military surplus is used as fish habitat and that lesson has begun to filter down to aquaculture.  It seems when structure is installed in what would otherwise be a barren raceway or pond, the fish congregate around the structures for food and shelter.  Unfortunately, put a pile of cinderblock and two-by-fours in the middle of your raceway and you may encounter a few logistical hurdles that need to be overcome.  From that seemingly obvious lesson spawned an entire market of manufactured structures known as AquaMats.   By combining the natural habitat, food production, and biofiltration functions of natural seagrass beds and coral reefs, the developers of AquaMats are revolutionizing aquaculture by bringing these natural environmental conditions into the commercial rearing of fish and other aquatic animals and showing remarkable successes in doing so. 

Working Within The Food Chain

The idea of using habitat in tanks and ponds is certainly nothing new.   The innovations that AquaMats have brought to aquaculture and commercial biofiltration are their ability to reproduce and support a natural balance in environments that are nothing like nature.  At first glace, these structures dont look like much more then shredded plastic bags floating with the current, but upon closer inspection the genius of this technology becomes apparent.  The surfaces of these structures are designed and manufactured specifically to grow periphyton, a collection of benthic algae and bacteria, which attaches and grows on submerged surfaces.  Just like trees that filter carbon dioxide and produce oxygen, the periphytic community metabolizes toxic by-products like ammonia, nitrites, heavy metals and other problematic nutrients into non-toxic forms, which are then available for the plants to use for growth. 

The more places you offer for periphyton to grow, the more periphyton youll produce.  The more periphyton you have, the more of a biofiltration capacity your system will have.   This is not a new concept; every mechanical/biofilter ever produced runs on this simple concept of surface area dictating biological uptake and conversion.   But what makes an AquaMat unique is that the actual biofiltration is only part of the picture.  You see periphyton is also a very valuable food resource to herbivorous and omnivorous fish as is the zooplankton, copepods and countless other animals that are produced as a result of this community.  By introducing surface area you close the loop on the food chain.  In essence, waste from the fish becomes fertilizer for primary production and eventually fish biomass rather than washing out of the effluent.  If fact, AquaMats have proven to be such effective filtration units that they alone are designed to provide biofiltration to zero exchange aquaculture systems as well as remediation in the municipal and industrial wastewater industries.  The concept is simple; by adding AquaMats you give your water and its inhabitants the ability to reach a balance.  Instead of trying to manipulate and control all the aspects of the environment, you give it the tools so that it establishes and maintains a balance, which is after all what nature does.  And for your troubles, the system produces healthier fish, which ultimately leads to a healthier bottom line. 

Oh Give Me A Home

So now we know that AquaMats produce cleaner water through natural filtration, which has the benefit of also being an excellent supplementary food source.  Still thats only half the story.  Extensive studies on natural rearing and on AquaMats specifically continue to show the value habitat offers to aquaculture.  When structure is provided, measurable differences in Cortisol, an indicator of stress, has been shown. This reduction in stress has been attributed to higher survival despite double and triple stocking densities, near elimination of Dorsal Fin Erosion, notable resistance to various diseases such as Bacterial Kidney Disease (BKD) and increased growth rates, which produce fish that grow faster and are harvested larger.  

Another benefit to Natural Rearing techniques is using habitat to train behavior in the animals in an environment that is more like what they would encounter in the wild.  One of the biggest problems faced by hatchery managers involved in release programs is that fisherman often complain that the fish are too easy to catch.  Most monitoring groups record post-release survival of hatchery raised animals at dismal estimates.  And it makes sense doesnt it?  A fish raised without the benefit of habitat doesnt know how to hide from a predator or forage for food or even hunt for that matter.  So why would we assume that an animal, even one as driven by instinct as a fish, could adapt to a completely new environment quickly enough to survive in it.  

By offering structure like AquaMats, survival is increased not only in the facility but in the wild due to predator avoidance and the behavior traits learned in the presence of habitat during rearing.       

By combining these aspects of food production, biofiltration and habitat management, AquaMats are changing the face of aquaculture for the future.  But more than the technology itself, they represent a profound understanding that is occurring in this industry.  It is human nature to try to manipulate our environment to our benefit.  But what we are slowly learning is that nature has already answered most of the questions we seek and by incorporating the natural functions of the environment in the things we do, it is much easier for us to achieve those benefits.  Natural Rearing is just one more step towards a sustainable industry but moreover, it is a step closer to understanding the world around us and the lessons it has to offer. 

 Selected Case Studies

University of Miami, Rosenstiel School of Marine and Astmospheric Science

The University of Miami in cooperation with the Aquaculture Center of the Florida Keys, a commercial fish hatchery, are currently conducting research on the use of AquaMats in mesocosm systems for the semi-intensive husbandry of mutton snapper (Lutjanus analis).  Each system was fitted with AquaMats to reduce levels of NH4 and act as a natural habitat for larvae and organisms in with the mesocosm.  Preliminary results indicate rates of growth and development of L. analis is faster in outdoor mesocosms containing AquaMats than indoor intensive systems.  In fact, first year results marked a 30% growth rate increase and the average weight of the fish improved 25%.

Bozeman Fish Technology Research Center, US Fish and Wildlife, Bozeman, Montana

The Bozeman Fish Technology Research Center has conducted research studies implementing AquaMats technology since 1997.   Research has focused on the use of AquaMats to provide natural habitat for trout species to reduce the stress of raceway culture operations and to increase survival of fish released into the wild. Results during 1997 included a 15% increase in survival of trout species reared with AquaMats in raceway trials and marked improvement in the dorsal fin index (DFI) values, which rose from 2.9 in controls to 8.3 in AquaMats raceways.  (DFI is an indicator of stress as measured by dorsal fin erosion.  A DFI of 10 is considered ideal.)  Additionally, the average weight gain of fish in the AquaMats raceways was 11% greater than controls.  During 1998, trials indicated that AquaMats raceways experienced far-reduced vulnerability to bacterial kidney disease (BKD), with BKD appearing with 80% less frequency in raceways provided with AquaMats. Trials were also conducted to determine the quantity of structure necessary to optimize survival in western slope cutthroat and rainbow trout.

Montana Warm Water Fish Hatchery, Montana Department of Fish, Wildlife and Parks, Miles City, Montana 

Extensive field trials were conducted during the 1997, 1998 and the 1999 growing seasons to optimize the use of AquaMats with five different species of warm water game fish, including walleye, largemouth bass, smallmouth bass, northern pike, and sturgeon. Average survivals for walleye with use of AquaMats have increased 40% over the past three years as compared with controls in ponds ranging from 0.5 to 3.0 acres in size. The culture work was conducted exclusively with live feeds generated in ponds, either with or without AquaMats. Fertilizer use has been reduced by 70% in AquaMats ponds (compared against controls) and fish stocking populations have been simultaneously increased by 33% over the three year period.  During its work with AquaMats, the Miles City facility has become the largest walleye hatchery in the US, handling 158 million eggs in 1999.

In addition to pond trials with fish, the Miles City facility relies on AquaMats for Flow Control as a filter field to reduce the sediment load of in-coming water for their 52-acre facility.  AquaMats for Flow Control reduced the average sediment load by 62% during the first year of operations.  This reduction of incoming sediment load had the beneficial effects of vastly reducing the acreage devoted by the facility to settlement functions and also reduced operational costs.     

North Carolina State/Smithfield Foods Inc. (commercial biofiltration application)

Effective and low-cost treatment of farm waste is a significant and important challenge for our nation.  Smithfield Foods, Inc., in cooperation with North Carlonia State and industry partners specializing in wastewater treatment, has worked aggressively to meet this national challenge. 

Like many commercial farm operations, the Smithfield Foods site in Duplin County has relied principally on anaerobic pits for treatment of a combined waste stream of solid and liquid waste.  Their objective was to receive water from an existing anaerobic pit (to include recycled liquid used to flush barns) and treat that water in an aerobic lagoon to (1) reduce ammonia and VOC levels of discharge water (2) reduce nitrogen loads for land application of effluent (3) reduce concentrations of Phosphorus and other metals in effluent and (4) reduce noxious odors.   

Pond Fertilizing Procedure Used At The Lac du Flambeau Indian Reservation
By:  Larry Wawronowicz (Natural Resource Director)

The ponds are partially filled approximately 4 weeks before the walleye fry are stocked. Initially, the ponds are fertilized and filled to one third the pond volume.  This allows the water to warm up faster which speeds up the establishment of zooplankton.  Surface water from Pokegama Lake is used to fill the ponds, which is the same water source used to hatch walleye eggs.  We are able to observe the zooplankton in the unfiltered hatchery water.  When the zooplankton is observed, the water from the lake is again pumped to capitalize on the plankton present in the lake water.  An additional one third of the volume is filled when we first see the plankton in the hatchery water and the final one third is added when walleye eggs start to hatch. 

The amount of fertilizer used largely depends on pond fertility, weather conditions, number and size of the fish and the quality and quantity of the zooplankton population.  Generally, we apply a total of 1,171 lb/acre of alfalfa meal and 115 lb/acre of Torula yeast.  The fertilization program usually begins by applying approximately the total amount of fertilizer required when the pond is first filled, and subsequent applications are weekly. Each weekly application is about 1/8 of the total amount of fertilizer required during the production season. See the Table below.

For more detail see Wawronowicz, L. J., and W. G. Allen. 1996. Walleye fingerling production techniques in drainable ponds on the Lac du Flambeau Indian Reservation. Pages 111-113 in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames.

Pond Fertilizing Procedure Used At The St. Croix Indian Reservation
By:  Donald Taylor, Field Supervisor, St. Croix Reservation

Here is a brief overview of how we fertilize our natural (undrainable) walleye ponds.  As a general rule, we would like to fertilize our ponds at least two weeks before the fry are stocked, which allows for a spike in zooplankton numbers. But, our department has a small staff and the spring is very busy with incubation and spring walleye assessments.  As a result we generally don't have time to fertilize.  We may still fertilize if after fry stocking we notice that the ponds are clear and plankton samples show low numbers. 

Our natural ponds are surrounded by agriculture fields and normal run-off brings ample amounts of nitrogen and phosphorus into the ponds.  Looking back in our records, we really could not find any correlation between harvest numbers and fertilizing.  There were times when we did not fertilize and had good harvest numbers and there were other times when we did fertilize but harvest numbers were below average.  Also, we had heavy algae blooms in years when we did not fertilize, yet no algae blooms when we did fertilize.

When we do fertilize we use "Arco" alfalfa meal and "Diamond V" yeast, both come in 50 lb bags.  We try to use 100-lbs/surface acre of both types.  The procedure is relatively easy, in that we open the bags and spread the fertilizer out evenly over the coverage area using a Jon boat.  What we do not want is to have the fertilizer "clump" out and then rest on the bottom of the pond.  We try to have the entire water column receive the fertilizer.

Besides fertilizing, what we really try to do is collect zooplankton and stock them into the ponds.  We go to the local wastewater treatment plants and get permission to collect the zooplankton.  On good days, a person can collect huge amounts of all sizes of zooplankton. 

Collecting them involves chest waders, a plankton dipnet, gauntlet gloves, and 5-gallon buckets.  We haul the zooplankton in our distribution truck, but you may use the buckets with lids.  We also bring a small pressure sprayer filled with a chlorine mixture to sterilize everything down after each use. 

 If timed correctly, the transfer of zooplankton 
could be a savior to the walleye fry.

Our natural ponds are controlled by elements beyond our control, which fortunately have usually worked to our benefit.  In the past we measured specific water quality parameters, but limited time, manpower, and funding have led us to stop measuring.

Pond Fertilizing Procedure Used At The Leech Lake Indian Reservation
By: John Ringle, Fish & Wildlife Director, Leech Lake Reservation

Introduction

The Leech Lake Tribal Fish Hatchery was first constructed in 1984 and expanded just two years later in 1986. This 25,000 square foot indoor complex contains rearing tank space in addition to an 80 jar egg incubation battery. Due to increasing production needs, construction began on a 10 acre drainable pond complex in 1993. This state of the art hatchery facility has a total capacity of about 1,500 quarts of eggs and indoor rearing space for about 400,000 whitefish fingerlings. Once the outdoor pond complex was completed, an additional 500,000 fingerling are were able to be reared. In addition, this program uses some of the small natural lakes on the reservation, as well as some natural rearing ponds on the White Earth Reservation, to cooperatively rear walleye fingerlings.

Annual fish production is 8 to 10 million walleye fry, 50,000 walleye fingerlings, 400,000 lake whitefish fingerlings, and when the need arises, trout, bass, cisco, and panfish are also produced. In addition, upwards of 20,000,000 white sucker eggs are collected annually. These eggs are incubated, hatched and sold to bait growers who in turn rear and sell them as fishing bait.

All of the game fish are stocked back into lakes and streams on the reservation for tribal subsistence harvest as well as tribal and non-tribal recreational fishing. Whitefish support a tribal commercial fishery and other nongame fish species are also commercially harvested by tribal members. A commercial bait harvest industry, regulated by the Leech Lake Band of Ojibwe also exists.

Pond Fertilization protocol for a 1 acre walleye pond:

• Ten days prior to stocking add 500 pounds of alfalfa meal
  and 50 pounds of brewers yeast.
  
  
  After initial fry stocking:

• This is followed by weekly applications of alfalfa meal (50 pounds)
  and 5 pounds of brewers yeast.

Fertilization Procedures for Pond Culture in Ohio Ponds 
By: David Culver, Department of Zoology, The Ohio State University 

The following is an excerpt that was reprinted from the Walleye Culture Manual, NCRAC Culture Series 101

A number of walleye and saugeye production problems have been addressed using limnological strategies. Four of these problems are highlighted below, along with the means for their solution.

1) Maintaining an adequate abundance of copepods and cladocerans for fish growth and survival: We encouraged growth of small algae (diatoms, coccoid greens, flagellates) for growth using liquid inorganic fertilizers once per week to achieve an inorganic N:P ratio of 20:1 by weight. The ratio began changing immediately upon fertilization, but we restored it to 20:1 once per week. We stocked fish at 4-5 d of age and filled ponds at the same time using reservoir water. High densities (over 50/L) of zooplankton were not necessary to provide adequate food for fry at stocking. Walleye consumption per day per fish was very low initially and increased exponentially with time. The zooplankton bloom grew along with the walleye's appetite, and we avoided overgrazing by Daphnia by stocking sufficient fish to prevent overabundance of Daphnia in week 4 or 5.

2) Avoiding high ammonia concentrations in the ponds, especially during the clearwater phase during week 4 or 5: We measured nutrients in ponds once a week and fertilized up to a target inorganic P concentration and N:P ratio, rather than using one fixed fertilizer amount.

3) Avoiding low oxygen concentrations: We used no organic fertilizers. For each unit of photosynthetically-produced biomass, one unit of oxygen is released to the water; for each unit of heterotrophically produced biomass, one unit of oxygen is consumed.

4) Avoiding large filamentous green and blue-green algae: We maintained a low phosphate concentration, favoring those algae (mostly small species) whose phosphate uptake mechanisms become saturated at low concentrations. Addition of large amounts of fertilizer at one time, especially when ponds are filled, favored large filamentous phosphorus storers, so we fertilized often with small amounts of N and P. We restored the N:P ratio in the pond to 20:1 once per week to minimize growth of nitrogen-fixing filamentous blue-greens. Also, we found many filamentous greens and blue-greens grew heterotrophically on the bottom of the pond, especially in those ponds to which organic fertilizers such as alfalfa meal had been added. When ponds cleared up, these algae were still rich with phosphorus from the sediments and were able to photosynthesize sufficiently to produce oxygen bubbles, which caused them to float up to surface just when we wanted to harvest fish.

We use liquid nitrogen and phosphorus fertilizers from agricultural suppliers exclusively. For nitrogen fertilization, we use 28:0:0, which is a combination of urea and ammonium nitrate. All hatcheries now use phosphoric acid (0:54:0) as a phosphorus source. None of the agricultural fertilizers we have purchased contained exactly the amounts of N and P expected. Nevertheless, for planning purposes, 28:0:0 fertilizer has about 4 lb N/gal (480 g NIL) (half as urea), and phosphoric acid is about 3.3 lb P/gal (396 g PJL). A typical 1-1.2 acre pond with no inorganic nitrogen or reactive phosphate will receive 1.3-1.6 gal of the former and 10 fl oz of the latter. We have also used 10:34:0 liquid fertilizer (ammonium phosphate) plus 28:0:0 to obtain the desired additions, but the calculations are simpler using phosphoric acid and 28:0:0. Hatchery staff has reported no difficulties working with concentrated phosphoric acid, provided care is exercised, and they appreciate the much smaller volumes that need to be used. Measurements must be accurate. Once the N and P concentrations of fertilizer and ponds are known, we use them and the volume of each pond at the current water level to calculate the amounts of N and P fertilizers to add to each pond that week.

As noted above, we only use liquid inorganic fertilizer. Not only does organic fertilizer contribute to oxygen problems but it is also not possible to alter the relative amounts of N and P in organic fertilizer, nor is it possible to know with certainty when or where the N and P contained in organic fertilizer will be released into the pond. Inorganic fertilizers are also less expensive than organic fertilizers.

Liquid fertilizer is added to the tank of an agricultural sprayer that is attached to a tractor and diluted with 50 gal of pond water. Then the solution is sprayed over the surface of the pond as the tractor travels along the dam. Some practice is required to time tractor speed to spray the entire contents of the tank in one pass. Measuring out the fertilizer went quickly using carboys with spigots for dispensing the phosphoric acid and larger polyethylene tanks with valves for the nitrogen fertilizer. In practice, the N and P are depleted by the next week in most ponds.

The progress of the seasonal bloom of algae was followed with weekly algal counts or more frequent measurements with a Secchi disk. Secchi transparency can be seen to decrease and then increase as imperfect evidence of an algal bloom that builds and declines as a result of a zooplankton bloom that occurred in the ponds. The dynamics of the algae and zooplankton can also be followed by their indirect effects on water chemistry. For example, oxygen declined throughout the season as the algae declined. Lower algae abundance resulted in lower photosynthesis, resulting in lower oxygen concentration. The pH tends to be high when photosynthesis is high and declines later in the season.

Fish growth is monitored weekly, and the pond draining is influenced by whether growth exceeds 1 mm/d, apparent condition of the fish, and whether they are >25mm. Fish are usually harvested when they are 30-40 mm; larger fish are easier to harvest, as they are less likely to be pressed against the screens on the kettle by the draining currents. Growth is affected by stocking density, but it is difficult to follow this through the season, since survival is not 100% and one cannot know with certainty when mortality occurred. If we assume that most mortality occurs the first week after stocking, however, we can compare growth of fish living at different densities using their abundance at harvest. Walleye and saugeye attained larger size at harvest densities below 32,000/acre. Above that density, however, fish size at harvest stays constant up through at least 144,000/acre.

These techniques may need to be adjusted for other locations where lower or higher inorganic carbon content (alkalinity), warmer or colder water temperatures, or differently shaped ponds might alter the dynamics of the system. For example, we use lower phosphorus additions in our deep ponds and in lakes. Still, chemical and biological monitoring of the production season and high stocking density have successfully decreased the variability among ponds, while increasing the number and weight of fish produced per acre.

Pond Management Tips

• Pond fertilization is one of many methods of managing your pond to increase production. Because the number of fish that can be produced in a pond greatly depends on water fertility, fertilization may improve the quality of fish growth, if the watershed in which your pond is located is poor in natural nutrients. However, while fertilization can benefit your pond, improper management can lead to significant problems such as excessive aquatic vegetation or oxygen depletion.
• Adequate oxygen can be maintained by removing excess vegetation from the water and by keeping pond banks fairly open, allowing wind to circulate the water. If heavy snow covers the ice during winter, scraping it clear can let sunlight penetrate and stimulate photosynthesis. If you choose to aerate your pond, consider a bubbler system rather than one which sprays water into the air. A bubbler can circulate the water efficiently, and it's much less energy-expensive to pump air than to pump water.
• Excessive growth of aquatic plants and algae are the most frequently received complaints from farm pond managers. Controls for nuisance plants can be physical, chemical, or biological. For physical control, shallow areas of the pond should be deepened by mechanical dredging and the pond sides should have 3:1 slopes. Watershed management that avoids leaching from fertilized fields, manure or sewage can help minimize algae mats and other problems.  Chemical weed control is a seasonal approach which, if done properly, can eliminate weeds and still leave the water suitable for other uses. Mats of algae, identified by their thick, hair-like appearance, are controlled best with copper sulfate. Submerged weeds can be held in check by a number of aquatic herbicides. Emergent plants like cattails are easily killed by glyphosate herbicides labeled for aquatic use. With any herbicide pay very strict attention to the label instructions and precautions.  
• Fertilization may not necessarily increase the size of individual fish, though it can help increase the total poundage.
• Ponds with excessive water flow should not be fertilized. In ponds such as these, you are probably wasting time and contributing to nutrient overload, or enrichment, in waters downstream from your pond.
• Ponds with extensive areas less than two feet in depth should not be fertilized. The addition of nutrients will only worsen the problem with overgrowth of aquatic vegetation.
• Ponds that have acidic soils should not be fertilized before proper liming. Proper liming allows the phosphorus to be available to the phytoplankton and not become bound up on the soil.
• The total hardness of the pond and soil pH should be checked every 3 to 5 years. If liming is required, apply at the recommended rate and that should improve the ability of the pond to develop adequate blooms.
• Ponds that are constantly muddy should not be fertilized. Phytoplankton require sunlight for growth and if the pond is constantly muddy, it is most likely that insufficient sunlight is penetrating the water to allow proper phytoplankton blooms to develop.
• A poor, infrequent fertilization program is worse than no fertilization program at all. Infrequent fertilization can result in fluctuations in the food chain and, therefore, food that is available to the fish populations. Infrequent fertilization can also add to aquatic weed problems.
• Once rooted aquatic vegetation begins to become established in a pond, you should not fertilize. The addition of inorganic nutrients at this time will only result in worsening the aquatic vegetation problems.