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The Genetic Frontier: How Transgenic Fish Are Revolutionizing Aquaculture

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* By Maharshi Limbola and Arya Singh.

Transgenic fish have been the subject of studies for the aquaculture sector with the goal of increasing growth rates, strengthening disease resistance, changing body composition, serving as biological factories for medical proteins, and even changing color and temperature tolerance. Transgenic fish technology is increasingly being used to produce fish with advantageous characteristics, such genetically modified food and environmental bio monitors.

Nowadays, molecular biology is advancing at a pace never seen before. Genetical engineered animals are one of them. An animal classified as transgenic is one whose genome has been altered to incorporate genes from a different species or to apply methods for editing the animal genome to produce particular features. One can intentionally modify a gene (or genes) to change an animal’s traits.

Transgenic fish have been the subject of studies for the aquaculture sector with the goal of increasing growth rates, strengthening disease resistance, changing body composition, serving as biological factories for medical proteins, and even changing color and temperature tolerance. Transgenesis will probably have a significant impact in the future. Transgenic fish technology is increasingly being used to produce fish with advantageous characteristics, such genetically modified food and environmental bio monitors. This article reviews the principle of the transgenic fish technology as well as its application in basic research and biotechnology applications.

Introduction

Transgenesis is the science of producing a genetically modified organism, which is somewhat easier to do in the fishes than compared to mammals. The reason behind that is fishes’ bred easily and lays large number of eggs which is totally different in the case with mammals. The main reasons to genetically engineer fishes are to boost the growth and capability of food conservation, and beneficial in order to enhance tolerance to environmental factors, like temperature as well as salinity. It is beneficial to introduce new color variations of attractive fish when it comes to fish. Producing fish with disease resistance is another benefit of transgenesis.

Many production techniques of transgenic fish have been refined, with each offering advantages and drawbacks that call for additional advancements. Both conventional selective breeding and transgenic approaches are necessary to supplement dramatically increase future food requirements because of the growth in human population. Although there has been considerable impact by selective breeding technology toward the production of fish, the process is slow and time-consuming; in the case of a genetic advancement through direct gene manipulation of a transgenic approach, it might take only years (Kiran et al., 2016).

Transgenesis is progressive study of making genetically changed fishes. The growing demand of fishes in global market has attracted massive research in the area of fish genetics and modification of organisms to make genetically modified organisms.

Previous years have witnessed immense development with the fast-growing industry and demand of AquaBounty salmon. AquaBounty salmon envisions to reach goal of 55,000 tons of salmon fishes annually by the year of 2028. First gene transfer in the fishes opened the gates of opportunity for development. This study deals with the status of transgenic fish specially AquaBounty salmon. The transgenesis concept plays a key role in science and technology.

In 1989 AquaBounty technologies genetically engineered (GE) Atlantic salmon that was named as AquAdvantage salmon. The growth hormone-regulating gene from Pacific Chinook salmon, which possesses a promoter sequence from ocean pout, was used to replace the growth hormone-regulating gene from Atlantic salmon. The genetic modification of salmon enables them to grow continuously throughout the year, rather than being limited to growth only during the spring and summer months (Devlin et al., 2006). These GE salmon are a cost-effective alternative to wild-caught salmon and traditional fish farming of unmodified salmon.

The primary goal of the modification is to accelerate the growth rate of the fish without altering its final size or other characteristics. Fish-farmed Atlantic salmon already exhibit faster growth rates compared to wild fish due to traditional selective breeding practices.

But instead of taking the typical three years to reach market size, genetically engineered salmon can grow even faster—in just 16 to 18 months (Kaufman, 2010). A single copy of the opAFP-GHc2 construct, which contains a promoter sequence from the ocean pout, was introduced when AquAdvantage salmon were produced in 1989 (FDA, 2010).

What basically happens is foreign genes are integrated into the genome of fishes, that are then inherited and expressed by their future generation. A quicker and more dependable way to modify the genetic makeup of several fish species is through direct gene editing, which is one of the most effective transgenic procedures (Devlin et al., 2001).

Maclean et al. (1992) reported the first transgenic fish generation in aquaculture using rainbow trout, and goldfish was the first ornamental transgenic fish (Zhu et al., 1985). Over time, a transgene encoding a growth hormone gene was inserted in an attempt to accelerate the growth of over 20 teleost species.

However, despite 25 years of progress in the development of transgenic fish, there is currently just one transgenic food fish available worldwide, along with pet fish such as zebrafish (Danio rerio), goldfish (Carassius auratus), and medaka (Oryzias latipes) for fundamental research. Nowadays, transgenesis is generally recognized as a potent tool for research in the developmental biology of model fish, particularly zebrafish and medaka.

Current Status of Transgenic Fish in the World

Genetic engineering has been the most promising technique to revolutionize society in the last forty years. For use in aquaculture, industry, and medicine, a variety of transgenic fishes have been created, comprising transgenic lines that express growth hormone. Since the gene sequence for growth hormone is largely conserved, a growth hormone construct was used to create the majority of transgenic fishes. The fish that underwent genetic modification shown a remarkable enhancement in their growth rate, indicating the beneficial application of transgenic technology in aquaculture (Cressey, 2009; Hu et al., 2007; Marris, 2010).

Afterwards, because of concerns related to bio safety, the auto-transgenic method was used effectively. Other than the growth trait, traits of resistance against disease and cold or hypoxia tolerance and Feed conversion ratio (FCR) upgradation were also considered for transgenesis.

The first transgenic food fish produced was called as “AquAdvantage Salmon” that has better ability to grow in quick manner and size when compared to salmon of  wild type. Seafood fish with improved growth, known as AquAdvantage Atlantic salmon (Salmo salar), has been licensed and marketed by the US Food and Drug Administration (FDA).

Based on the most recent data, the list of developed transgenic fishes is shown in Table 1.

The most commonly used gene in transgenic research is growth hormone, which is primarily used to increase the rate of growth. Growth hormone, metallothionein, antifreeze protein, nanocrystals, and regulatory genes such promoters are currently employed in transgenic fish studies. Heat shock protein, myosin light polypeptide chain 2, keratin, and metallothionein are among the promoter sequences that are successfully used for a variety of purposes to stimulate gene expression (Asaduzzaman et al. 2013). In order to combat stress conditions, the inducible and tissue specific promoters (eg. HSP70) were used (Halloran et al., 2000).

Many fish have been used as models to detect heavy metal pollution, such as cadmium, mercury, zinc, and copper, using metallathionin promoter. Fish prototypes, including medaka and zebra fish, have been utilized all around the world to answer biological issues and aid in drug development. For example, GFP has been employed as a reporter while using estrogenic vitellogenin gene promoters to track reproductive activities in medaka (Zeng et al. 2005b).

National Status on Transgenic Fish Production

In India, research on transgenic fishes goes long back, it has been reported first in 1980. When it comes to fishes, Madurai Kamaraj University, National Matha College, Kollam and Centre for Cellular and Molecular Biology, Hyderabad transgenic research started transgenic fish production using borrowed constructs from different countries. Year 1991, was the first time transgenic fish was generated in Madurai Kamaraj University using Growth hormone constructs.

In order to prevent biosafety issues, the Indian Council of Agricultural Research (ICAR) has also taken the initiative to participate in and support transgenic fish research programs for the development of auto-transgenic fishes like rohu and catla. Numerous experimental transgenic fish, including zebrafish, catfish, and rohu, have evolved this. According to that research, auto-transgenesis is less controversial and safer than dangerous (Rasal et al., 2016).

In ICAR-CIFA, the group of scientists started to work on transgenic fishes and reported many papers regarding the basic researches, gene therapy as well as transgenics (Barman et al., 2010; Mohapatra et al., 2010). The working β-actin gene promoter of rohu carp, that has ability to do driving ubiquitous expression, was granted (Barman et al., 2015). The separated β-actin gene promoter/regulatory region are conserved among Indian major carps. This promoter can be vital in order for any species of interests for foreign gene expressions. Opposed to this, the isolated of the rohu (Labeo rohita) mylz2 promoter (1.2 kb) can also be used in order to expression in targeted skeletal muscle (Barman et al., 2015).

Conclusion and Future Perspectives

The transgenic fish has become important since it improves fish production and indirectly reduces scarcity of food and facilitates livelihood. A promising approach in this is the development of sterile transgenic populations that are prevented from contaminating a natural gene pool. Such fish should then be made according to the Cartagena Protocol and the regulation on bio-safety.

The potential of transgenic fish is great, but further studies are also necessary to understand the effects by which they can be properly integrated into ecosystems. Careful and accurate risk assessments related to this technology use, especially on biodiversity and ecological impacts, are thus inevitable. Sterile transgenic fish must be utilized in aquaculture as a precautionary measure against biodiversity risks. Transgenic approaches combined with selection techniques and marker-assisted breeding should be used to create lines of fish of precise performance characteristics.

It is very important that the fisheries scientists be active monitors of the performance and ecological impacts of transgenic fish. It also lies in their interest to form public policy on their development and eventual release into the wild. Detailed risk assessments need to be conducted to ensure that released transgenic fish would not impact the wild population. Additionally, gene inactivation strategies with the aid of gene editing technologies may further enhance the economic value of transgenic fish, most especially by favoring species that produce higher yields in flesh and better food conversion ratios.

References and sources consulted by the author on the elaboration of this article are available under previous request to our editorial staff.
Maharshi Limbola
College of Fisheries Science, Veraval – 362265
Arya Singh
ICAR-Central Institutes of Fisheries Education, Mumbai – 400061
Corresponding email: maharshilimbola@gmail.com

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