Importance of genetic principles
The importance of genetic principles to aquaculture development was recognized by the international community when it drafted the FAO Code of Conduct for Responsible Fisheries. Article 9.3 requires that "States should conserve genetic diversity while maintaining integrity by suitable management of the ecosystems and aquatic communities" (FAO, 1997)
General technical guidelines to help implement the Article have been developed that address brood-stock selection and management. The use of gmo's interaction of wild and farmed animals is being release and introduced. Genetic stock identification techniques are being used in fishery management to assess species stocking procedures and to determine mixing of aquaculture and wild stocks, as well as to assist in determining the composition of mixed stock fisheries (Brodziak et al., 1992).
1984 data from the Mediterranean regarding aquaculture production, reported only 6 species to FAO. These consisted mostly of shellfish, some mullet; sea bream culture and sea bass was just beginning. So far reported data on Mediterranean farmed species amounts to between 20 and 30.
Improvements of plant crops and livestock based on modern breeding methods are in contrast to the few examples of breeding programmes that exist for fish, an example being the Atlantic salmon in Norway. Therefore such genetic principles could be applied to the farming of marine species, greatly increasing the cost effectiveness through improved breeding methods.
Such technological applications can be grouped into short term and long term improvements.
Short term improvements for example sex reversal and hybridization chromosome set manipulation, is made over one to two generations. The improvements generally constitute a one off events. Another example of a long-term improvement programme is selective breeding where small gains accumulate over generations. Gene transfer may also be employed as a long-term strategy where the gains become significant, allbeit non accumulative from progeny to subsequent generation. Many of these technologies can be combined and used collectively.
Lately calls for the reduction of detrimental environmental effects by means of genetic intervention have been forth coming, specifically in the advent of farmed species escaping into the natural environment. Equally the applications of these techniques have been scrutinise from both ethical and moral standpoints. The challenge is how effectively manage and promote the new diversity, while conserving the natural genetic diversity among aquatic species. Invariably more and more aquatic species will become domesticated as breeding techniques become more efficient thus creating potential socio-economical, technical and biological quandaries (Welcomme R.L.1988)
Future implications for genetics and biotechnology in the marine environment
According to Bartley and Hallerman (1995) surveys of international attitudes on biotechnology revealed that developed countries expressed a strong desire to utilize aquatic species as bio-reactors. Transgenic rabbits have been produced with a salmon gene that produces calcitonin that helps to control calcium loss in humans. (Electronic Telegraph March 25, 1997). Tilapias are being engineered genetically in Canada to produce human insulin (Mackenzie,1996).
These applications are important activities for the aquaculture industry however more data needs to be collected and disseminated to all parties involved in fisheries science, as there is insufficient information on the genetic characteristics and the inheritance of those characters, of fish in natural waters. Assessment of genetic resources will encourage the development of programs to preserve and evaluate genetic integrity. There needs to be more development regarding the procedures for the preservation of natural gene pools. Also there is a need for the evaluation of strain, hybridization, polyploidy and sex reversal in fish (.Welcomme, R.L. 1988)
Also genetic inbreeding is potentially problematic and needs to be mitigated. Additionally, problem solving improves fishing strategies and reduces environmental stress caused by overfishing. Research is currently underway to study and isolate the natural ``antifreeze'' compounds found in the blood of marine organisms, and to eventually leverage the underlying chemical modifications in applications as diverse as additives for the automotive engine fluids and tissue and cell storage media for cryogenic processes. Many potential applications may arise from the creative reuse of the present-day functional diversity found in nature (Sager, B.2001)
Genetic technologies can be utilized in aquaculture for a variety of reasons, not just to improve productivity. Improvements in marketability, cultivability, and the conservation of natural resources can be facilitated by the appropriate genetic technology. Genetic improvement programmes can also be used to provide short-term or long-term gains The short term gains are usually immediate, within 2 generations, and generally not cumulative (unless combined with other long-term programmes), whereas the long term programmes such as selective breeding produce small gains that accumulate each generation (Falconer, 1981). In general, genetic improvement technologies have not been applied to marine species to the same extent as they have been applied to freshwater and anadromous (salmonid) species. Thus, as more marine species become farmed, genetic improvement can be expected to play an increasingly important role in improving production.
The growth of the aquaculture sector has raised concerns on its risk to the environment and native species through the large-scale release or escape of farmed animals and their subsequent breeding with, competition with, or predation on local species; farmed aquatic animals may also be a vector for disease transmission to wild stocks. Aquaculture has been recognized as the primary reason for the purposeful movement (introduction) of aquatic species (Welcomme, 1988) and experience has shown that cultured species usually escape into the wild. Hatchery or farmed fish have been assumed to represent a risk to the native gene pool by introducing maladapted genes, i.e., genes adapted to the farm and not to the wild (Hindar et al., 1991). However, Campton (1995) pointed out that direct evidence for adverse effects resulting from the mixing of hatchery and wild stocks is difficult to come by. As genetic techniques increase in their frequency of application and in their alteration of the phenotype, there may be more concern for environmental bio-safety.
Although the use of hormones early in the culture of aquatic animals is becoming widely accepted due to the fact that no residue remains when the organism reaches market size, certain areas still have restrictions on the consumption of fish that have been treated with hormones. (Dunham, 1995) Religious and ethical concerns may also affect the application of some genetic technologies in aquaculture. Transferring genes between species may be viewed as an abomination of nature.
Some new technology may also be objectionable to animal-rights activist due the level of increased suffering in some of the improved animals, as in the case of arthritic transgenic pigs, or some transgenic Coho salmon that may starve due to underdeveloped mandibles (Devlin et al., 1994). Transgenic organisms may also contain new allergens that were not present in the non-transgenic form as in the case of a Brazil nut gene introduced into soybeans. The Pioneer HiBrid seed company developed a transgenic soybean with a gene from the Brazil nut; the protein produced by the transgenic plants elicited an allergic response in natives who previously were not allergic to non-transgenic soybeans. The company has discontinued the marketing of the transgenic soybean (Nordlee et al., 1996).
Marine biology and health care
Discussions have been made regarding the biodiversity loss implications for the global environment; however it is only recently been noted the serious and direct effects on the health of humans. Biodiversity loss affects the spread of human diseases and causes a loss of medical models, for example the studies carried out by Eric Davidson and colleagues, to understand endomesoderm specification in sea urchin larva, demonstrate the power of a systems approach to understanding developmental processes. The sea urchin is an excellent model for studying development because it exhibits a simple mode of development and the fertilized egg divides within a day or so into the five territories that constitute the major tissues in the larva. It is noted that the biodiversity loss diminishes supplies of raw materials for drug discovery and biotechnology, also threatening water quality and food production. (Grifo, F. et al 1997)
The use of marine organism in traditional medicine has a limited historical record, nonetheless the oceans, constitute over 70% of the surface of the earth which represents an enormous resource for the discovery of potential chemotherapeutic agents. The National Cancer Institute. Of America (NCI) after decades of Bio-prospecting has implicated a species of New Zealand sponge as a source for halichondin (a potential anticancer drug). The NCI is currently testing natural products in 30 countries in an attempt to find potential treatments for cancer, AIDS and other diseases sciencedaily 2007)
The first notable discovery of biologically active compounds from marine sources was the serendipitous isolation of the C-nucleosides, spongouridine, and spongothymidine, from the Caribbean sponge, Cryptotheca crypta, in the early 1950s. These compounds were found to possess antiviral activity, and synthetic analogue studies eventually led to the development of cytosine arabinoside (Ara-C) as a clinically useful anticancer agent approximately 15 years later, together with Ara-A as an antiviral agent. The systematic investigation of marine environments as sources of novel biologically active agents only began in earnest in the mid-1970s. These studies have clearly demonstrated that the marine environment is a rich source of bioactive compounds, many of which belong to totally novel chemical classes not found in terrestrial sources. Until recent no compound isolated from a marine source has advanced to commercial use as a chemotherapeutic agent, though several are in various phases of clinical development as potential anticancer agents. The most prominent of these is bryostatin 1 which was, isolated from the bryozoan, Bugula neritina to date; bryostatin has been in more than 80 human clinical trials, with more than 20 being completed at both the Phase I and Phase II levels.
(Cragg, G.M. et al 2005)
A discovery has been made in America by the researchers at the Scripps Institution of Oceanography; bacteria found in mud in the Bahamas, has the potential to help fight cancer.
A pharmaceutical company has now used the information that the bacteria's genome has been successfully sequenced, to treat bone marrow cancer patients. (. Sciencedaily 2007)
Salinispora tropica is a bacteria discovered in 1991 in the shallow ocean sediment off the Bahamas, it is related to the Streptomyces genus, a group of land-based bacteria renown as an antibiotic-producing organisms. After the bacterium's genome was successfully sequence it was confirmed that Salinispora produces natural antibiotics and anti-cancer agents. It was discovered that 10% of the bacteria's genome is utilised for producing molecules for antibiotics and anti-cancer agents, compared to only 6% to 8% of most organisms' genomes. Consequently the ability to decode this bacteria has lead to a host of implications for isolating and adapting potent molecules from marine organism for example salinosporamide A, is currently in human clinical trials for treating multiple myeloma, (a cancer of plasma cells in bone marrow), as well as for treating solid tumours. Another example of a marine species used for the advancement of medicine is the sea hare, Dolabella auricularia from the Indian Ocean; it is the source of more than 15 cytotoxic cyclic and linear peptides known as dolastatins. It entered Phase I clinical trials in the 1990s, and progressed through to Phase II trials as a single agent, but has been dropped due to lack of significant activity. As a result of the synthetic processes, many derivatives of the dolastatins have been synthesized with TZT-1027 (Auristatin PE or Soblidotin) now in Phase II clinical trials in Europe, Japan, and the United States. Sponges are traditionally a rich source of bioactive compounds in a variety of pharmacological screens and a number of sponge-derived agents are in clinical development as potential anticancer agents These include the polyhydroxylated lactone and discodermolide isolated from the Caribbean sponge, Discodermia dissoluta HTI-286, a synthetic analogue of hemiasterlin originally isolated from a South African sponge, Hemiasterella minor ,and soon thereafter from a Papua New Guinea sponge from the genus Cymbastela; and a synthetic analogue (E7389) of halichondrin B which was originally isolated in 1985 from the Japanese sponge, Halichondria okadai, and subsequently from Axinella sp. from the Western Pacific, Phakellia carteri from the Eastern Indian Ocean, and from Lissodendoryx sp. off the east coast of South Island, New Zealand . Girolline isolated from Pseudaxinyssa cantharella, and LAF-389, a synthetic analogue of bengamide A, isolated from Jaspis coraciae, advanced into clinical trials, but were dropped due to lack of efficacy Other marine-derived compounds currently in clinical trials against cancer include Ecteinascidin 743, isolated from the Caribbean ascidian Ecteinascidia turbinata ; aplidine, the dehydro analog of didemnin B, isolated from the Caribbean tunicate, Trididemnum solidum kahalalide F, isolated from the Hawaiian mollusc, Elysia rufescens spisulosine, isolated from the marine clam, Spisula polynyma squalamine, isolated from the common dogfish shark, Squalus acanthias,collected off the New England coast . The cryptophycins are metabolites isolated from a terrestrial cyanophyte (Nostoc sp.) and an Okinawan sponge, Dysidea arenaria, and a semi-synthetic derivative, cryptophycin 52 (LY355703), progressed to Phase II clinical trials, but was withdrawn in 2002
The extremely potent venoms (conatoxins) of predatory cone snails (Conus species) have yielded complex mixtures of small peptides (6-40 amino acids), which have provided models for the synthesis of novel painkillers (e.g., Ziconotider) which currently is in a pivotal Phase III trial Advances in the understanding of bacterial aromatic polyketide biosynthesis have led to the identification of multifunctional polyketide synthase enzymes (PKSs) responsible for the construction of polyketide backbones of defined chain lengths, the degree and region-specificity of keto-reduction, and the region-specificity of cyclizations and aromatizations, together with the genes encoding for the enzymes. Since polyketides constitute a large number of structurally diverse natural products exhibiting a broad range of biological activities (e.g., tetracyclines, doxorubicin, and avermectin), the potential for generating novel molecules with enhanced known bioactivities, or even novel bioactivities, appears to be high. Genome sequencing is figuring out the order of DNA nucleotides, or bases, in a genome: the building blocks that make up an organism's DNA. Since DNA sequencing methods can only handle short stretches of DNA at a time the entire genome can't be sequenced at once Genome sequencing is deciphering the order of DNA nucleotides, or bases, in a genome: the building blocks that make up an organism's DNA Recent research has revealed that deep ocean sediments are a valuable source of new actinomycete bacteria that are unique to the marine environment. Based on combined culture and phylogenetic approaches, the first truly marine actinomycete genus named Salinospora has been described, members of the genus are ubiquitous and are found in sediments on tropical ocean bottoms and in more shallow waters, often reaching concentrations up to 104 per cc of sediment. They also appear on the surfaces of numerous marine plants and animals. They can be cultured using the appropriate selective isolation techniques, and significant antibiotic and cytotoxic activity has been observed, leading to the isolation of a very potent cytotoxin, salinosporamide A; a very potent proteasome inhibitor. A recent example of the power of this technique when applied to natural products is the development of an efficient method for scale-up production of epothilone D , currently undergoing clinical trials as a potential anticancer agent. Epothilone D is the most active of the epothilone series isolated from the mycobacterium; Sporangium cellulosum it is the des-epoxy precursor of epothilone B The isolation and sequencing of the polyketide gene cluster producing epothilone B from two S. cellulosum strains has been reported, and the role of the last gene in the cluster, epoK, encoding cytochrome P450, in the epoxidation of epothilone D to epothilone B has been demonstrated. Heterologous expression of the gene cluster minus the epoK into Myxococcus xanthus resulted in large-scale production of crystalline epothilone D The total synthesis of complex natural products has long posed challenges to the top synthetic chemistry groups worldwide, and has led to the discovery of many novel reactions, and to developments in chiral catalytic reactions More recently, the efforts of some groups have been focused on the synthesis and modification of drugs that are difficult to isolate in sufficient quantities for development. In the process of total synthesis, it is often possible to determine the essential features of the molecule necessary for activity (the pharmacophore), and, in some instances, this has led to the synthesis of simpler analogues having similar or better activity. A notable example is that of the marine-derived antitumor agent, halichondrin B mentioned earlier.
In 1992, the synthesis of both halichondrin B and norhalichondrin B was reported and the synthetic schemes were utilized to synthesize a large number of variants of halichondrin B, particularly smaller molecules that maintained the biological activity, but were intrinsically more chemically stable, due to the substitution of a ketone for the ester linkage in the macrolide ring. Two of these agents were subsequently evaluated by NCI in conjunction with the Eisai Research Institute in the United States, and one of the compounds, (NSC 707389/E7389) is now in Phase I clinical trials The synthesis of the epothilones by several groups has permitted the preparation of a large number of designed analogues and detailed structure-activity studies, which have been reviewed These studies have identified desirable modifications, which might eventually lead to more suitable candidates for drug development, but thus far none of the analogs has been reported to surpass epothilone B in its potency against tumour cells (Cragg, G.M.et al 2005)
All but two of the 28 major animal phyla are represented in aquatic environments, with eight being exclusively aquatic or predominately marine prior to the development of reliable scuba diving techniques some 40 years ago, the collection of marine organisms was limited to those obtained by skin diving. Subsequently, depths from approximately 3 to 35 meters became routinely attainable, and the marine environment has been increasingly explored as a source of novel bioactive agents. Deep water collections can be made by dredging or trawling, but these methods suffer from disadvantages, such as environmental damage and non-selective sampling. These disadvantages can be partially over- come by use of manned submersibles or remotely operated vehicles (ROVs); however, the high cost of these forms of collecting precludes their extensive use in routine collections
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