The term "aquaculture" is sometimes used to mean any form of cultivation of aquatics, which includes growing of fish for bait or aquaria as well as for food, or even stocking of natural waterways. I am using it here in the more limited and common sense of production of aquatic organisms under controlled conditions (more or less) for use as food. That point is important, particularly to aquaculturists who resent being painted with a broad brush, when considering the history of exotic invasions in the Great Lakes. A general survey of all documented introductions between 1810 and 1991 conducted by some of the leading researchers in the Great Lakes, often cited in the literature, ascribed 29% of total introductions to "unintentional releases," including aquaculture. But their actual coding of 33 species of aquatic fauna - including fish, mollusks, crustaceans, oligochaetes, other invertebrates, and bacterial and protozoan pathogens - included none that were actually classified as releases from "aquaculture" per se.⁽¹⁸¹⁾ In fact, a case can be made that "aquaculture" - in the limited sense distinct from older practices of cultivating new species of fish in natural lakes and rivers, which were associated with the introduction of the alewife, common carp, furunculosis, and Glugea hertwigi - has never been clearly associated with a significant introduction to the Great Lakes.⁽¹⁸²⁾ (One exception may be whirling disease, caused by Myxobolus cerebralis, a protozoan whose mechanism of release is unclear, although it was first documented in an Ohio aquaculture facility.⁽¹⁸³⁾) Thus, proponents of the aquaculture industry may argue that there is no scientific basis for even considering that industry to be a vector of concern.⁽¹⁸⁴⁾

That is an argument, but one which is not persuasive, if for no other reason than the fact that aquaculture is a relatively new and expanding industry in the United States and Canada. Fishery managers tend to look back at artificial stocking in natural lakes and rivers as the precursor to modern aquaculture, and then lump them together in the classification of "unintentional releases" or "intentional introductions," because those were the closest historical precursors. More to the point, there are perfectly logical reasons to be wary of accidents occurring as a result of the expansion of aquaculture in the future regardless of the lack of clear historical or empirical proof of danger. With the possible exception of certain closed recirculating aquaculture facilities, one must assume that any organism widely cultivated will have opportunities to escape. Exotic species used for aquaculture are likely to be exactly the sort of species successful at invasion if released by reason of their adaptability to the climate and strong breeding characteristics. As one scientist puts it, there are "ecological perils implicit in the characteristics of those species that make those species ideal for aquaculture."⁽¹⁸⁵⁾ The really big and bad ones such as the sea lamprey and the zebra mussel come along only infrequently, and each has its own unique history. One might have learned, from the devastation of the sea lamprey, that the key is to watch out for what swims up the canals. But that historical lesson was not good preparation for the invasions of the European ruffe and the zebra mussel in ballast water. Attempts to attack these problems "scientifically" with careful statistical analysis are of limited value as a guide to evaluating future threats.⁽¹⁸⁶⁾

In fact, up until now the great preponderance of aquaculture in the United States has used native catfish and trout species, with almost half of total production (49%) being catfish, which has been concentrated in the southern states. But the industry is now beginning to make more use of exotics such as African tilapias and Asian carps.⁽¹⁸⁷⁾ An exotic blue tilapia which escaped from aquaculture in Florida has established itself in the Everglades, where it is causing serious damage to native fish and vegetation.⁽¹⁸⁸⁾ Considering that there have been few exotic fish used in aquaculture in the Great Lakes in the past, just as there have been few alligators cultivated here, it therefore is not particularly significant to observe that we have suffered few invasions from exotic fish or alligators from aquaculture in the past.

The best expert opinion on the nature of the threat comes from the US National Science and Technology Council Joint Subcommittee on Aquaculture (JSA), which is a strong proponent of aquaculture development. The JSA has identified the following "challenges" in their national plan for aquaculture in the United States:

As US aquaculture continues to expand, it must be sustainable and environmentally compatible. We need substantially better knowledge about possible interactions between aquaculture and natural environments to minimize the potential for habitat degradation, disease transmission, genetic dilution of wild stocks through interbreeding with cultivated strains, introduction of non-indigenous species into natural waters, and discharges of wastes, toxins, and excess nutrients.⁽¹⁸⁹⁾

Aquaculture in the United States and Canada is very much on the beginning or "take off" segment of the S-curve so familiar to both ecologists and economists. That does not mean that it can safely be predicted to climb to the top of the curve. It just means that current growth is relatively rapid, beginning from very low levels, and that it has definite potential. Promotional literature for the development of aquaculture often points out that fish farming was first practiced as long ago as 2,000 BCE in China.⁽¹⁹⁰⁾ Nevertheless, aquaculture is still more of a potential than a major economic activity at the end of the Twentieth Century.

It did not begin in the United States, and then only in a rather limited form, until the last part of the Nineteenth Century. Up until the early 1960s, it was fairly restricted in the types of fish cultivated, and "Many of these early attempts at fish husbandry failed…."⁽¹⁹¹⁾ Aquaculture in the United States includes catfish, salmonids (predominantly trout), mussels, oysters, shrimp, and even alligators. The oldest, largest, and most economically viable sector of aquaculture is the farming of catfish in the southern states. (Catfish accounts for 49% of total production⁽¹⁹²⁾ and 84% of the increase in US production from 1983 to 1993.⁽¹⁹³⁾) Even this is small scale, although it has been growing. Catfish farming has gone from approximately 400 acres in 1960 to 161,000 acres in 1991, with 59% percent of that in the State of Mississippi.⁽¹⁹⁴⁾

Generally, aquaculture in the United States has been described as "the fastest growing agricultural sector, with production increases of 265 percent reported between 1980 and 1993."⁽¹⁹⁵⁾ However, "Despite this rapid growth, domestic aquaculture still provides less than 10 percent of the nation's total seafood supplies. Over 40 percent of the fish and shellfish consumed in the US is imported…."⁽¹⁹⁶⁾ (And that, it must be remembered, is a limited part of the US diet. Although seafood has been increasing in popularity, the average per capita consumption of seafood in the United States was still only 15.5 pounds in 1990.⁽¹⁹⁷⁾) The most recent figures available from the JSA show that aquaculture production for food in the United States in 1997 weighed in at 774 million pounds and was valued at $717 million.⁽¹⁹⁸⁾ (Not a staggering amount in a national economy with a GNP of over 7 trillion in 1995. But it does represent a simple annual average growth of 17% in weight and 19% in value during the last ten years of 1987-1997.)

In the "North Central Region" of the United States, a US Department of Agriculture (USDA) region which includes all of the Great Lakes states except Pennsylvania and New York, the two predominant species are catfish and trout. The largest percentage of catfish producers in the North Central region are in Missouri, Kansas, Illinois, Ohio, and Nebraska (in that order) and the largest percentage of producers of trout are in Wisconsin, Michigan, and Minnesota (in that order).⁽¹⁹⁹⁾ Wisconsin production has a "current" estimated value (probably based on mid-1990s figures) of $8.8 million a year.⁽²⁰⁰⁾ Pennsylvania, the leading state in the USDA's "Northeast Region," produced trout worth $16 million in 1995, but it is unclear how much of this was in the Great Lakes watershed.⁽²⁰¹⁾ Aquaculture in the Province of Ontario has been almost entirely production of rainbow trout, by reason of provincial policy, although the Ontario Ministry of Natural Resources significantly widened the number of species allowed for production in 1995.⁽²⁰²⁾ The great majority of the Ontario aquaculture facilities are in the "southern peninsula" between Lake Huron and the eastern lakes, squarely within the Great Lakes watershed. Ontario production came between 7.0 and 7.5 million pounds and C$12.5 to C$14.0 in 1995.⁽²⁰³⁾

As a matter of basic physics and biology, aquaculture has an obvious potential for producing high-quality protein far more efficiently than terrestrial agriculture.⁽²⁰⁴⁾ But small-scale producers frequently meet with unpleasant surprises in the form of large capital investments required for the facilities,⁽²⁰⁵⁾ the difficulty of maintaining consistent water quality (including problems with levels of heat, air, nutrients, and toxins, the problem of handling waste water), and the problems of preventing spread of diseases in highly concentrated and stressed populations. Aquaculture facilities are quite varied in design and degree of sophistication. They may consist of isolated ponds, cages connected to public waters, artificial raceways (almost exclusively for trout), and closed recirculating systems. Ponds, which may resemble the layout of terrestrial agricultural fields, require a lot of land. Cages (highly disfavored by US Great Lakes conservation agencies) result in discharge of wastes to public waters and present a high probability of escapes. Raceways require specialized construction and a good source of fresh water, unless they are combined with a water recirculating system. Closed recirculating systems, which may resemble huge, factory-like aquaria, require expensive pumping, feeding, cleaning, and water control equipment. But they can be highly productive and environmentally clean. One closed recirculating facility in Pennsylvania produces 500,000 pounds of hybrid striped bass, tilapia, steelhead, and yellow perch in huge tanks while recirculating 98% of its water.⁽²⁰⁶⁾ From the point of view of preventing both escapes of exotics and discharge of harmful wastewater, these systems are much preferred over the others, especially the cages.⁽²⁰⁷⁾

The fish or their eggs may come from anywhere. This includes (1) natural stocks in the same watershed (which almost always require a permit from the conservation authorities), (2) cross-trading between different aquaculture farms (which may require little in the way of permits and documentation), or, (3) more commonly, one of a relatively small number of large farms (which will usually require some sort of permit or health certification from agriculture or conservation authorities). Most of the trout producers in the eastern United States buy eggs from large farms in the western United States.⁽²⁰⁸⁾ Sources for stock used in the Great Lakes region varies. For example, Michigan brook and brown trout eggs are produced almost entirely within Michigan,⁽²⁰⁹⁾ but most of the rainbow trout producers in Michigan buy eggs from a single large supplier in the State of Washington, which sends them by air freight, along with a certification that they are free from disease. ⁽²¹⁰⁾

Aquaculture diseases. Disease is a major concern for the aquaculture industry. Many of the same pathogens which have minimal effects in the natural environment become a serious problem for aquaculture fish because of their high densities, poor water quality, inadequate nutrition, and poor sanitation.⁽²¹¹⁾ In addition, the transportation of fish for use in aquaculture, even if not exotic species, has the potential to transport exotic pathogens which can have a serious impact on native strains of the same species with less resistance to those pathogens.⁽²¹²⁾

The Joint Subcommittee on Aquaculture (JSA) has observed that "the US government's ability to prevent and control aquatic animal diseases is presently inadequate. The government's effectiveness is impaired by a fragmented, uncertain, and incomplete Federal regulatory framework, often characterized by disagreements among agencies with roles and responsibilities in aquatic animal health."⁽²¹³⁾ Also, the lack of a "competent authority" for aquaculture disease control at the federal level in the United States (meaning, technically, one agency with clear authority over the issue) has been of concern to authorities in the European Union, who do not generally consider US regulation of the industry to be up to par.⁽²¹⁴⁾ The US Animal and Plant Health Inspection Service (APHIS) in the US Department of Agriculture (USDA) is developing regional laboratories for better certification of US agriculture products for export.

On the import side, the Michigan Department of Agriculture (MDA) and Michigan State University (MSU) are working to develop cheaper and faster laboratory techniques for the identification of diseases in fish imported for aquaculture,⁽²¹⁵⁾ and the Great Lakes Fishery Commission (GLFC) has published a model program for controlling pathogens in salmonid imports.⁽²¹⁶⁾ The GLFC guidance is provided to aquaculturists, but not actually required to be used, under the Michigan Aquaculture Development Act.⁽²¹⁷⁾ MDA has active programs, in coordination with the Michigan DNR, for monitoring specific diseases such as the whirling disease, which is common among salmonids.⁽²¹⁸⁾ (Whirling disease is caused by Myxobolus cerebralis, a protozoan originally exotic to the Great Lakes, whose mechanism of release is unclear, although it was first documented in an Ohio aquaculture facility.⁽²¹⁹⁾)

The diagnosis of diseases depends on specific protocols, developed by biologists and veterinarians in response to specific outbreaks. Nor do there even seem to be any established field or laboratory protocols for the detection of a wide number of pathogens known to be present in non-salmonid species of fish around the world,⁽²²⁰⁾ but not yet known to be a problem in the Great Lakes. Disease diagnosis, for fish as well as humans, requires a fair amount of expertise and experience.⁽²²¹⁾ It also requires an opportunity to observe the population providing the eggs under controlled conditions. The fact that the industry is structured in such a way that most imported eggs are supplied by a small number of large and easily identified farms offers government regulators an excellent target of opportunity for quality control of the supply. But that requires some effective exercise of authority at federal and international levels.

Genetic modifications bear on the exotic problem in two ways. Genetic modification can be used as a method for preventing invasions. Grass carp and other salmonids which have been modified at the point of fertilization to have an extra set of chromosomes, making them "triploids" instead of normal "diploids," are thereby made sterile. This has been particularly desirable in the case of grass carp because they are useful in the control of exotic and other nuisance aquatic weeds. It may also have collateral benefits for aquaculture in that triploid fish will not fully mature, and thus maintain more desirable flesh.⁽²²²⁾ But this technique is far from foolproof. It requires careful testing of stocks (using blood tests) to insure that no normal diploids are present. Contrary to early expectations, a diploid male may be able to impregnate the eggs of a triploid female. Also, experiments with oysters indicate that some sterilized organisms can revert back to a fertile state.⁽²²³⁾

Genetic modifications, through either simple selection and inbreeding or more sophisticated techniques for modifying genes or transplanting them from one organism to another ("transgenic" organisms) amount to human creation of exotics. Some species, such as salmon, may be deliberately selected for characteristics which make them more suitable for aquaculture, such as lower aggression, but which have the potential to be harmful if spread to the native stock.⁽²²⁴⁾ More generally, the simple fact that the inbred stocks have less genetic diversity can cause ultimate loss of genes in the native population.⁽²²⁵⁾ Such inbred strains have not been considered a major threat to biodiversity by many biologists, based on good experience with terrestrial organisms. But some researchers point out that "terrestrial breeding programs may not be an appropriate model upon which to base regulations for the aquatic sector, partly because so much of aquatic biodiversity is found in wild populations,"⁽²²⁶⁾ and others warn that the escape of exotic cultured stocks could cause "devastation."⁽²²⁷⁾ The potential for contamination of native stocks by genetically modified fish is considered a matter of concern by the United Nations Food and Agriculture Organization (FAO).⁽²²⁸⁾

A vice president of the World Bank has said that "The next great leap in producing food will come from 'domesticated' and genetically improved varieties of fish and other seafood."⁽²²⁹⁾ The only US policy statement on the issue seems to be the general note of concern in the "challenges" quoted above in the JSA plan for aquaculture.⁽²³⁰⁾ The Canadian Government is actively promoting a "biotechnology strategy" which includes creation of transgenic fish and other aquatic organisms.⁽²³¹⁾ That program is led by the Department of Industry (Industry Canada). The Department of Fisheries and Oceans (DFO) is supportive of the Industry Canada plan, but somewhat more cautious about the use of transgenics. DFO notes that "transgenics, such as carp that have the rainbow trout growth hormone gene, are considered by some as new organisms for which there is little existing information relevant to their behavior, interaction, or performance in the wild; nor is there any appropriate theoretical basis for prediction."⁽²³²⁾