Farmed Seafood and Canadian Health: How Higher Seafood Consumption Can Save Lives
Click the link below to see the report prepared for The Canadian Aquaculture Industry Alliance
November 2013
CLICK HERE FOR REPORT
Despite widespread use of the androgen 17α-Methyl Testosterone (MT) in tilapia farming, the implications of tilapia hormone treatment in relation to human health and the environment have not been well articulated to the fish trade, or the general public. The purpose of this white paper is (a) to explain clearly why MT is widely used by the producers of farmed tilapia; and (b) to demonstrate why there are no risks to consumers, and no known risks to producers or the environment, provided the recommended best practices for MT use in aquaculture are followed. These best practices are described, so that tilapia dealers can ensure that their suppliers are taking the necessary steps to protect consumers, fish farm workers and the environment.
Click HERE to download and read the complete paper.
AQUACULTURE IN THE AMERICAS
By Kevin Fitzsimmons
Department of Soil, Water and Environmental Science
University of Arizona, Tucson, Arizona, 85706
Click HERE to download a pdf of article.
Introduction to Tilapia Sex-Determination and Sex-Reversal
Kevin Fitzsimmons
University of Arizona
One of the basic factors of tilapia aquaculture is that male fish grow bigger and faster than the females. Also, in order to avoid unwanted spawning in a production unit, all-male populations are preferred. There are several methods used to skew sex ratios and increase the percentage of males in a population.
The first method developed was to simply cull through a population, discard the females and keep the males. This system is obviously wasteful and inefficient. In the 1960’s and 70’s, Israeli scientists discovered that certain hybrid crosses resulted in skewed sex ratios favoring males. There are several theories regarding the genetic factors involving the number and location of sex genes on particular chromosomes. The use of hybrid crosses is still one of the primary methods of producing mostly male populations. The drawback to this method is that two separate broodlines must be maintained. The crossing must be done very carefully and meticulous records should be kept to insure that the parent species are kept pure. Also, usually only one sex from each species is used for any particular cross because the reciprocal cross (using the other sex from each species) is not as successful. Another problem is that the number of young produced is rarely as high as a single species spawn. Therefor, to maintain a commercial scale hatchery will usually require significant resources and staff.
The more common method of generating mostly male populations is through the use of steroids fed to sexually undifferentiated fry. Newly hatched tilapia are still developing their gonads. Even though they are determined genotypically their phenotype, or morphological characteristics can still be altered. By exposing the fish to forms of [...]
By Kevin Fitzsimmons
University of Arizona
One of the great advantages of tilapia for aquaculture is that they feed on a low trophic level. The members of the genus Oreochromis are all omnivores, feeding on algae, aquatic plants, small invertebrates, detrital material and the associated bacterial films. The individual species may have preferences between these materials and are more or less efficient depending on species and life stages in grazing on these foods. They are all somewhat opportunistic and will utilize any and all of these feeds when they are available. This provides an advantage to farmers because the fish can be reared in extensive situations that depend upon the natural productivity of a water body or in intensive systems that can be operated with lower cost feeds.
In extensive aquaculture, the fish will be able to grow by eating algae and detrital matter and the farmer can grow more fish in a given area because the fish are depending directly on the primary productivity of the body of water, primary consumers. Fish which feed on a higher trophic level, eating larger invertebrates or small fish, are secondary consumers and a system can only support a fraction of the biomass of secondary consumers compared to primary consumers.
In intensive systems, tilapia have the advantage that they can be fed a prepared feed that includes a high percentage of plant proteins. Carnivorous fish require fish meal or other animal proteins in their diets, which in general are more expensive than plant proteins. Nutritional studies which substitute plant proteins supplemented with specific amino acid supplements may lower costs, but still not to the level that can be achieved with tilapia diets.
Complete diets are used in systems that cannot provide any [...]
By Thomas D. Kocher
Department of Zoology & Program in Genetics
University of New Hampshire
Basic tilapia genetics
We are at an early stage in the genetic domestication of tilapia. During the approximately 40 year history of intensive culture, the genetic resources of tilapia have been poorly managed. The genetic problems now manifesting themselves are of several kinds. First is the loss of pure species through mismanagement of interspecific hybridization (McAndrew 1993), a technique which has been used to produce all-male fry which have a higher growth rate in production systems (Hickling 1960; Hulata et al.1983). One popular commercial strain is thought to contain genes from as many as four species (McAndrew et al. 1988). A second problem is high levels of inbreeding depression. Primary collections of wild broodstock frequently consisted of a small number of individuals. These were serially distributed, so that genetic problems have been passed from country to country, and farm to farm. Eknath et al. (1993) compared four strains farmed in the Philippines with four strains newly isolated from wild populations in Africa. The best performing strains were those most recently isolated from nature, consistent with the idea that domesticated strains suffer from inbreeding depression (Tave and Smitherman 1980; Hulata et al. 1986; Teichert-Coddington and Smitherman 1988). A survey of 18 microsatellite DNA markers in several commercial strains found some strains with heterozygosities less than 10% of that found in wild strains (Kocher et al., unpubl.). In addition to inbreeding, it is likely that negative selection for growth rate has occurred during the propagation of many stocks. Finally, there is evidence for contamination of genetically improved strains by introgression from feral species (Macaranas et al. 1986).
In recent years attention has focused on a single [...]
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