Is Fish Waste Compost worth the Mess and Effort?

Final Report for FS11-257

Project Type: Farmer/Rancher
Funds awarded in 2011: $9,848.00
Projected End Date: 12/31/2011
Region: Southern
State: South Carolina
Principal Investigator:
Dale Snyder
Sweetgrass Garden Co-op
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Project Information


1. Fish composting using a bio-filter compost bin liner and passive aeration is effective, with reasonable odor control.
2. Both fish and vegetable compost were more effective than no compost.
3. Fish compost was superior to vegetable compost based upon blinded, qualitative observation of plant size and vigor.
4. Late blight killed all the tomato plants in this study. However, plants in the fish compost group developed the disease later than plants in the veggie and no compost groups. We attribute this relative resistance to blight to better host defense, the vigor imparted by fish compost.


The Mayflower landed near modern day Plymouth in the spring of 1620. They had an immediate need to plant crops that would supply them through the following winter. The local soil was of poor quality, and fertility had been depleted by excessive farming by the indigenous people. Fortunately for them, the Pilgrims were not perceived as a threat by their new neighbors, who provided them with seed and instruction. The principle method for improving fertility was to plant a fish carcass in a raised hill with corn seed.

Thus, fish waste has long been known to be a useful soil amendment, a natural source of nitrogen. Fish meal is commercially available. And fish is a good source of nitrogen in compost. The problem with composting fish is odor, and the associated attraction of varmints. Developing an effective way to compost fish appeared especially attractive in our coastal community with extensive commercial fishing.

The purpose of the present study was to test a novel method for composting commercial fishing waste that mitigates odor, then to compare fish compost with organic vegetable compost in a garden test plot.

Project Objectives:

The purpose of the present study was to test a novel method for composting commercial fishing waste that mitigates odor, then to compare fish compost with organic vegetable compost in a garden test plot.


Click linked name(s) to expand
  • Betty Taylor
  • Dr. George Taylor


Materials and methods:

Composting: during the project we maintained four composting bins measuring 4x4x4 ft.

Fish composting:
Fish waste has provided by Mark Marhefka, a commercial fisherman in Mt. Pleasant, SC, who operates a fish cooperative by subscription. He fishes in the Gulf Stream for about 2 weeks each month, and his catch is shared by subscribers. Mark filets the fish, and what is left comes to us; previously it was dumped at sea. This includes the fish skeleton, viscera, head, tail and skin. This waste is saved in coolers and transported to Johns Island twice a month.
The compost was constructed in layers: 2 inches of fish (the thickness of a carcass), 4 inches of straw or leaves, and a half inch of garden soil. Odor was controlled with a bio-filter “liner”. The outer walls of the bin are constructed of two sheets of wire mesh stapled to the outside of a 2×4 inch frame so that there is a 4 inch compartment between the two layers of mesh(actually more than 4 inches because of bulging). This compartment is filled with finished compost. Thus, the cooking compost is enveloped by a 4+ inch wall of finished compost–a bin liner– that functions as a filter. It works well to block odor, but makes it difficult to turn the compost for aeration. Instead of turning, the bins incorporate a system of passive aeration. At the bottom of the bin four 5 inch poly sewer pipes are laid, and the pipe has perforations. Ends of the pipe extend beyond the bins, allowing free flow of air. As the compost heats, air moving through the pipes is drawn through perforations into the body of the compost, much as a hot chimney draws. The compost pile is watered as needed.

Vegetable composting:
We obtain organic vegetable waste from Whole Foods on James Island (a twice weekly pickup). The method of composting is identical to that described for fish, with wilted vegetables substituted for fish waste. There is no need for the bio-filter bin liner, but we do use the passive aeration system described.

Test Garden:

During this first season, we compared the efficacy of fish vs vegetable compost on tomatoes. Better Boy tomato plants were purchased from a local supplier. There were six alternating rows using fish compost, veggie compost, or no composite, and each row had 30 plants. Rows were positioned 5 feet apart, and plants were spaced 36 inches apart. Before planting the composted rows, a
4 inch layer compost was laid and worked into the soil by hand. Three weeks after planting, the plants were side dressed using the same compost.

The rows were numbered so that blinded observation was possible (without knowledge of which compost was used in the row). There were two pre-specified end points. The first was the size of the tomato crop by weight, to be expressed as tomato weight per plant (with about 60 plants in each of the three treatment group). The second was a blinded, qualitative evaluation of plants, an estimation of plant health and vigor. For this part of the study, we enlisted two observers: Roger Francis, our Clemson agriculture extension agent, and Joseph Fields, a Johns Island farmer with long experience. Their grading system was admittedly crude: we simply asked them which plants–if any–looked better.

Research results and discussion:

The fish composting method worked well. A day after building the compost pile there is fish odor apparent within 10-15 feet of the bin. At that time flies collect on the surface of the bin. After a week, the odor has dissipated, and with it, the flies. Without turning the pile, we have observed that the middle of the compost bin consistently heats to 130 degrees F. After 3-4 weeks, the fish compost cooks down to half its original volume, and the compost matures at 6-8 weeks. At that time no soft fish parts are visible. Small bones have decomposed, and the compost has a uniform, dark, mature compost feel. Only some large bones (scapulae and skulls) can be seen. The end product has no fish odor, but instead smells like healthy soil. Our experience indicates that use of a bio-filter bin liner would allow fish composting as close as 40-50 feet to a residence.
We found that the vegetable compost pile is not quite as hot as fish compost, maintaining a consistent temperature around 110 degrees F. It takes about 3 weeks longer for the vegetable compost to mature.

Test Garden:
Blinded, qualitative observation 4 weeks after planting confirmed more rapid growth of tomatoes fertilized with fish compost when compared with other test rows. The plants were larger and appeared more vigorous to our observers; they were not equivocal with this observation. Fish composted plants had maturing fruit 1-2 weeks earlier than those treated with veggie compost. Furthermore, the plants treated with vegetable compost looked better than those receiving no compost.
***One month after planting, the tomato plants developed late blight (the diagnosis of Roger Francis). Within a week of early symptoms, the plants were dead. To our surprise, at first the plants treated with fish compost seemed immune to the disease, and we wondered if we had stumbled on a cure. However, between one and two weeks after the appearance of the disease in plants in the veggie and no compost groups, the more robust appearing plants that received fish fertilizer developed blight and succumbed over the next week. By this time these plants had set fruit, and we were able to harvest 3-5 red tomatoes per plant, compared with no red tomatoes from the veggie and no compost groups.
As another measure of blight resistance, at the point in time that all of the tomato plants in the veggie and no compost groups were dead, just 50% of the plants in the fish compost group had signs of blight (another observation confirmed by Roger Francis).

***Details from the garden log: On April 9, 2011, Better Boy tomatoes were planted from starts in rows 4, 5, 6 and rows 8, 9, 10. Rows 6 and 10 were fish compost, and 4 and 8, veggie compost. Rows 5 and 9 received no compost. First tomato fruit was seen in row 6 on May 6, a fish compost row. Five days later, on May 11, first signs of blight were seen on two plants in row 4, a vegetable compost row, and row 5, a neutral compost row. On May 12, signs of blight appeared on one plant in row 6, but others in rows 6 and 10 remained healthy for another week. On May 25, Roger Francis made another observational visit. He documented that 100% of the plants in rows 4 and 8 showed blight, 92% of the plants in row 5 and 9 showed blight, and 50% of the plants in row 6 and 10 (fish composted) showed blight.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

This report will go on our website (Facebook Page), and will include pictures.

In addition, the Sweetgrass Garden Co-op had an open house on February 25, 2012, to highlight our fish composting operation. It was attended by 135 people who were able to inspect the compost bins at various stages of development (a fish bin that was less than one week old, and others 3 and 6 weeks along) There were local farmers and fishermen in attendence. Study participants were available to discuss composting in general, as well as fish composting.

Our second year with the garden test plot is in prgress, this year using eggplant (another heavy feeder). We hope to generate data on the effect of fish compost on yield. The result of the continued study will be published on our web site. In addition, we will submit a brief communication to popular garden journals describing fish composting.

Later this season, we plan to develop a marketing plan for “Sweetgrass Garden Fish Compost”, and hope to sell some in local garden centers, as well as our vegetable and flower stand.

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.