Based on an article by Steven Sullivan, Maccaferri Gabions, Inc.

 Photo 1
Photo 1:
Forage Development Site – Terryall River, CO

Over the past few years it has been brought to our attention that gabions are being used in not only a new, but rather revolutionary way. It could be a solution for several of the problems of fish hatcheries and the aquaculture of streams and rivers. Hal Hagen and his father, Dr. Darrel Hagen of Aquatic Alternatives, Buena Vista, CO, have been using gabions in their fish hatcheries and streams and have had great results. In order to investigate the use of the gabion structures, a team of Maccaferri personnel visited the Colorado streams where gabion structures are being used. One site was the Terryall River (Photo 1).
A full understanding of the aquatic environment is not possible in one day. The importance of the aquatic environment to the fish industry warrants, not only further investigation, but also verification of the results. Results in larger habitats have not been quantified, but data in smaller areas has been recorded.
The group felt overwhelmed with the amount of information and complexity of the relationships between fish and their environment. Hal Hagen is an expert in this field, and did his best to explain the interactions. A few of the points are discussed below.

 Photo 2
Photo 2:
Fecal Material in Hatchery Tank
Photo 3
Photo 3:
Water Recycling through Gabion Structure
 Photo 4
Photo 4:
Aeration Devise with Gabion Structure
 Photo 5
Photo 5:
Invertebrate Growth on
River Rocks – Terryall River, CO

The findings cover two specific areas: (1) The aquatic habitat in fish hatcheries, (2) The aquatic habitat in streams.
1) Fish Hatcheries:
The fish industry has many problems in need of solutions. Some of these problems include: Diseases that are prevalent in the fish hatcheries which degrade the quality and quantity of fish. Restocking of streams becomes a necessity. Hatchery fish are accustomed to eating artificial fish food and do not recognize the natural food found in the wild. Having been raised their entire life in concrete tanks and artificially fed they make poor quality game fish. The fish raised in hatcheries are poorly suited for life in the wild, and are either caught immediately or starve to death. The fecal material of the fish collects in the bottom of the tanks, is a disease carrier, limits the amount of fish that can be produced, and is a source of pollution to the streams (Photo 2). Because of this unnatural environment, the fish are not happy and have a high stress level, which hinders their growth and makes them more susceptible to disease. The concrete ponds are an unnatural environment and add to the stress level. A more natural environment, such as rocks, would reduce the stress level of the fish. Gabion rocks make a good bottom filter, through which the fecal material can be removed by pipes embedded in the bottom of the gabions. Water can be recycled through the gabions (Photo 3), air also being added to the water to improve the water quality (Photo 4), reducing the amount of water needed by a fish hatchery. The result is a fish of much higher quality, with fewer diseases, that is accustomed to natural food and a natural environment, better enabling it to survive in the wild. More fish can also be raised per cubic foot of water, and less food is needed.
2) Stream Habitat:
There are many problems facing this environment. The streams are over fished, have little food available, have few spawning pools, and the fry and fingerlings need areas for protection from larger fish. These problems can be amended by using gabions in streams. The first objective is to increase the amount of fish that a stream can support by increasing the amount of available food. This is done by installing gabions at strategic locations in the streambed. Leaves, twigs, etc., are trapped by the rocks, and then degrade, providing food for bacterial colonization and invertebrates (bugs, worms, stone flies, may flies, etc.); these later become food for the fish (Photo 5). There are not enough spawning beds, but these are a necessity for a self-sustaining fish population. Spawning structures can be constructed from gabions and larger rocks. Once the fry have hatched, they need protection from the larger fish. Gabion rock of appropriate size can provide the necessary protection. A total environment can be created, providing an abundance of food, a place to spawn, and protection for the fry and fingerlings. Results have been good, producing fish much larger than average, and at a faster rate.

Colorado Riparian Association