Growing Mealworms as a Fish Feed for Sustainable Aquaponics

Growing Mealworms as a Fish Feed for Sustainable Aquaponics

Summary

WORK ACTIVITIES

Mealworms were purchased and containers were modified to grow them in March of 2016.  The containers were recycled from food grade bins obtained from local restaurants.

Both 2-inch deep (shorter) and 5-inch deep (taller) sizes were modified by cutting rectangular openings in 2 places on each lid and gluing screen door mesh to these openings.  The openings were positioned so that bins could be stacked in a perpendicular manner on top of each other and allow for adequate ventilation of each container.

Initially 4 cups of substrate materials were placed in each of the two different sized containers with 300 meal worms in each container.

A subsequent set of four taller containers with 8 cups of substrate materials and 600 worms in each were started two weeks later.

Additional substrate materials and pieces of produce for moisture were added on approximately biweekly basis, as needed. Ratings were taken to evaluate estimated number of mealworms and activity, as well as depletion of substrate and moisture containing organic produce items.

Data loggers were added to existing ones and some were moved to track temperatures in greenhouses, soil, air, plant root zones, fish tanks and mealworm growing trays.

After about 3 months, it was determined that the shorter bins, although adequate for growth were less desirable than the taller ones.  Even though the substrate volume was reduced significantly from feeding by mealworms resulting in reduced dust sized particles, the taller bins would allow for more room for longer term growth.  Also, temperatures were likely to fluctuate more with the reduced air space above the growing media and drying was greater due to closer proximity to the screen openings in the lids of the shorter bins.  Therefore, the mealworms were all shifted into larger containers after this initial phase of evaluations.

Four different certified organic materials were evaluated as substrate media.  These were selected based on local availability and pricing and included rolled oats, rye flakes, spelt and red wheat bran.  A local organic bakery was the source for the rolled oats and spelt.  A local Whole Foods store was the source for rye flakes and red wheat bran.

Initial growth and maturation into adult beetles was slightly better for rye flakes.  However, both the spelt and wheat bran showed better feeding and more mealworms after several months than the rye flakes and rolled oats.  When sufficient quantities of adult beetles were observed, these were moved into a separate bin. The ones from the rolled oats and rye flakes were moved into a bin with a combination of both rolled oats and rye flakes.  The adults from the wheat bran and spelt were moved into separate containers with the same substrates that they were originally growing in.

After 4 months of evaluations, it was determined that the spelt and wheat bran had the best feeding and growth rates.  The rolled oats and rye flakes were not consumed as completely and the residual material was not small enough to allow for screening out of the mealworms to harvest for feeding to the fish.

The numbers and feeding activity observed was similar for both the spelt and wheat bran. Since the price was significantly higher for the spelt at more than double that for wheat bran and the growth rate was similar, after 6 months of evaluations, it was decided to focus on growing methods for maximizing production using the wheat bran alone.

Initial plans were for building a shaded containment area to grow the mealworms in the passive solar high tunnel greenhouse.  However, after initial observations of temperature fluctuations, especially air temperature spikes reaching over 100 degrees F, it was decided that use of a shaded room in the cooler renewable energy greenhouse would be more reasonable for the initial evaluations.  Plans will allow for increasing the supply of mealworms this spring and number of bins to the point where some bins will be moved to shaded containment in the passive solar greenhouse for further evaluation this summer.

The renewable energy greenhouse has supplemental propane heating and is set to keep temperatures above 45 degrees during winter months, however, temperatures as low as 40 degrees were recorded in the mealworm growing bins, as this room was far enough from the supplemental heat source to allow for lower temperatures during extreme colder nights.  It was observed that as temperatures dropped below 50 degrees, mealworm activity and growth was slowed significantly.  When temperatures dropped below 45 degrees, this resulted in the death of most of the adult beetles.  Until that time, no significant odors were observed from the growing bins. The dead adult beetles were not removed in the hopes that they might revive, but subsequent rotten smell proved that was not the case.  The activity of mealworms was only slowed at lower temperatures.  Some of the initially purchased mealworm larvae were even placed in the freezer for several days then thawed out without any loss of worms to determine if freezing temperatures would be an issue in the unheated passive greenhouse.

It was observed that during hotter summer days that the need for supplemental moisture was critical for growth.  Several different sources were evaluated, including potatoes, carrots, cucumbers, summer squash and apples.

Initially potatoes and carrot pieces were placed in shallow plastic container lids that allowed mealworms to easily access as the raised edges of the lids were low enough to not discourage any climbing over them.  Even with the shorter food bins, little to no climbing up the walls was observed.  Potatoes had a greater feeding rate than the carrots.  As they became available during the summer months both cucumbers and summer squash were evaluated as a source of water for the mealworms.

Cucumbers were favored and devoured at a quicker rate than other items.  However, subsequent screening to separate mealworms resulted in cucumber seeds needing to be picked out from screened mealworms.  Also, infestations of cucumber beetles limited availability of cucumbers and summer squash during the late summer months.  Apples were then evaluated.  The mealworms devoured these for the moisture at rates similar, but slightly slower than cucumbers, however, they did not digest the skins and these had to be removed as mold was observed growing on the remaining skins.  Also, fruit flies were small enough to allow them to multiply, as the screening material hole size was large enough to allow them to lay eggs on the apples.

It was also observed that slices about ¼ inch thick were the optimal size to allow for greatest surface area access by mealworms, as opposed to irregular sized pieces.

During the dryer summer months, consideration was also given to adding water to separate lids, however, due to concerns about encouraging mold growth in the substrate and the need to carefully add water on an almost daily basis due to evaporation, it was decided to continue to add pieces of produce items.

The moisture at times during the hottest summer months was seen as the limiting factor.  A miniature water bowl with some kind of float mechanism that would prevent any overflow getting mixed with the growing substrate would be ideal, but due to the bowl needing to be shallow enough to prevent the mealworms from drowning, the design would be a challenge. It may be possible use a sponge in a shallow tray, but automated watering may be difficult to match with consumption rates.  Since no such device has been located, pieces of potatoes and seedless cucumbers (as available) will continue to be the source of moisture for the mealworms moving forward, until another alternative delivery method is developed.

Labor activities for growing mealworms included container construction, adding substrate materials, providing sliced produce items to allow for sufficient moisture to encourage growth, separating out adults, recording temperature data, making observations and sample analyses.  More time than expected was spent separating out and moving adult beetles so that they would not feed on young larvae.  Screening before larvae are too large may be an option to minimize the amount of time for separating.

Nutrient analyses of the fish feed, Aquamax 400, and mealworms grown on wheat bran were completed in December.  Prior to analysis, the fresh weight versus dried weight of the mealworms was determined to be able to provide an adequate size sampling of fresh mealworms for laboratory analysis.

RESULTS AND WHAT WAS LEARNED SO FAR

• Mealworms were successfully grown in food grade bins recycled from restaurants that were modified with ventilation screening in the lids. The taller containers were more suitable for accommodating longer term increase of substrate materials.

• Wheat bran was determined to provide the most growth activity and to be the most cost effective organic substrate material that also allowed for an easy screening process to harvest mealworms when needed.

• Moisture availability is critical during hot summer months for mealworm growth. Cucumber slices were the preferred means for providing moisture for mealworm growth, however, seedless varieties will be grown next year to avoid seeds during the screening process. Potato slices were also suitable for use when supplies of fresh items grown on-site are limited and are currently a low cost option.

• Temperature ranges fluctuated more in the unheated passive greenhouse than in the main renewable energy greenhouse. The fish tank, located in the passive greenhouse, had temperatures similar to ground temperatures as they are 50% in-ground.  In spite of air temperatures as low as 0 degrees F this winter, the covered frames above the fish tanks prevented freezing of circulating water and plant materials and harvests were able to continue through the winter months.

• Temperatures below 45 degrees resulted in the death of mealworm adult beetles, but did not result in any dead larvae mealworms, however, slower growth and activity were observed at low temperatures and reduced yields of mealwoms are expected. This should not be a problem, as fish feeding is stopped whenever water temperatures drop below 50 degrees, which is generally from late November thru early February.  Quantities needing to be grown during summer months will need to be determined to have a sufficient amount for fish feeding.  Since freezing of mealworms appears to be a viable option for maintaining a reliable source of mealworms when thawed, over producing during summer months can provide adequate supplies for months when growth is slower than fish feeding rates.

• The dried weight of mealworms was determined to be 40% of the fresh weight. Dried weights sample analyses were virtually identical for the crude protein content of the fish feed and the mealworms. This means that to get the equivalent nutrients as from 1 lb of dried fish feed, 2.5 lbs of fresh meal worms will be needed.

• Significant amounts of mealworms will be required during the second phase of this project to provide adequate quantities for feeding the fish and more containers will be stocked with mealworms and wheat bran in late winter/early spring of 2017.

Dry weight analysis:

WORK PLAN FOR 2017

• The quantities of mealworms will need to be increased significantly to provide adequate amounts for the feeding phase. This will be accomplished prior to initiation of fish feeding as water temperatures increase above 52 degrees, usually in late April or early May.

• Separate bins will be evaluated to determine Feed Conversion Rates for yield of mealworm protein per pound of wheat bran over a six month period to be able to extrapolate potential economic feasibility for growing fish feed as compared to purchasing commercial feed.

• Plant growing bins will be emptied with new growing media and new plantings by early March. Based on market demands for the coming season, the planting ratio will be approximately 25% Mizuna and 75% Day Neutral Strawberries for each fish tank growing area. Separate yield records will be maintained for each growing area after replanting until the removal of the fish at the end of the growing season.

• Review of results indicates that several key nutrients may need further considerations.

Since the crude fat is higher than desirable for the mealworms, a preliminary study on a smaller sample of fish will be conducted to determine if the actual composition of the crude fat may be of concern for developing fatty livers. Not all forms of crude fats may be of concern. Further review with fish nutritionists will also be conducted.  Consulting with a fish vet may be needed to determine how to proceed for proper analysis of sampled fish.

Calcium and iron levels also appear to be significantly lower in mealworms and may need to be supplemented.

• Water sampling will be done to determine any need for supplementing minor nutrients through the biofiltration system for the mealworm fed fish tanks. Sampling will be done for both fish tanks and water source (pond water). Additional monthly sampling may be needed to maintain adequate minor nutrient levels.

• A preliminary smaller fish tank feed trial will be done with a small amount of bluegills and other fish species in early spring (prior to beginning feeding in the larger tanks) in the heated renewable energy greenhouse to determine if feeding with only mealworms could develop any problems.

• Feeding rates for the two larger passive greenhouse fish tanks will be determined based on dry weight nutrient analysis basis and the daily feed amount will be determined by minimum satiation rate of the fish, so that equal amounts will be fed to each tank throughout the growing season.

• Fish from each tank will be harvested and weighed for sale in early October when the water temperatures are suitable for fish pond restocking. Ten fish from each tank will also be analyzed for any fatty livers or other internal differences resulting from the feeding regimes.

• Plant tissue analyses will be sampled for both crops growing on top of both tanks in mid-summer as crops are actively growing.

• Since my main assistant, Katie Aukerman, has moved on to a full time position in October at a different location, a new project assistant will be hired this spring. Other part time labor was also used to assist with the adult beetle separation process during the summer months.

OUTREACH

• Three open greenhouse tours were held on May 14th, June 4^th and October 4th of 2016, with limited attendance due to poor weather conditions on all 3 dates. A total of 44 persons attended these tours.

• A North Central Region SARE tour group visited the farm on July 12, 2016, with a tour bus with a much larger group of about 80 persons.

• A video of this tour was posted on August 19, 2016 and linked on YouTube at:

https://www.youtube.com/watch?v=ikDJ783Nins&list=PLQLK9r1ZBhhEmeogq9tj0K2tRgeMLdZ8J&index=7  This site showed 298 views as of 1/29/17.

• Another site with this video does not post number of views:

https://www.youtube.com/watch?v=GFh9c6A-81c

• A speaker presentation was made at the Ohio Aquaculture Association Conference on January 26, 2016 with an estimated 40 persons in attendance.

• At least two more open greenhouse tours are planned for 2017.