Malaysia's aquatic ecosystems contribute 1.6% of her gross domestic product and provide employment to about 100,000 people. They are sources of a significant proportion of the nation's food supply, mainly by marine capture fisheries; but aquaculture, both marine and freshwater is becoming increasingly important. Hence, characterization of the species diversity of Malaysian biological resources (bioresources) is of paramount importance. One of the key components in any biodiversity investigation is elucidation of the population genetic structure of the species being studied, as it is an indication of the status of the species within the ecosystem. It is here that biochemical protein level and molecular DNA level indicators play crucial roles. Thus far, the studies that had been done in Malaysia using such biochemical and molecular markers were mainly on freshwater aquatic species that are important to aquaculture such as the catfish, Mystus nemurus and Clarias macrocephalus, and tilapia, Oreochromis niloticus and O. mossambicus, and the prawns Penaeus monodon and P. merguiensis. Random Amplified Polymorphic DNA (RAPD) and microsatellite markers had been used to study two species of marine turtles that nest on Malaysia's pristine beaches, the hawk's bill turtle, Eretmochelys imbricata and the green turtle, Chelonia mydas. However, none of the top ten marine fish species endemic in this country had been studied yet. A start had been made to study the genetic structure of the green-lipped mussel, Perna viridis, with a view to using it as a biomonitoring agent of environmental pollution. An association was found between increased heterozygosity level for allozyme loci and heavy metal pollution index in this species. This paper discusses these findings and makes suggestions for the use of biochemical and molecular markers as potential biomonitoring agents of pollution levels in future ecotoxicological studies of Malaysia's aquatic ecosystems.

Introduction

Since the 1980s Malaysia has embarked on an industrialization policy which transformed her from an agriculture-based economy to one based on industrial production with a vision of attaining a developed nation status by 2020. The standard of living of the country has improved dramatically as a result of this policy, but success in economic growth and industrialization has lead to environmental problems with ever increasing land, air and water pollution. Aquatic pollution is especially damaging for Malaysia because of her long coastlines on the Straits of Malacca and the South China Sea. Most of Malaysia's oil wells are offshore platforms in the South China Sea off the coast of Terengganu state on the east coast of Peninsular Malaysia and off Sarawak state on Borneo Island. In addition, maritime traffic in the Straits of Malacca, one of the busiest but narrowest international waterways between Peninsular Malaysia and Sumatra, Indonesia, is ever increasing, especially that of oil tankers. This strait is also the most important source of seafood for Malaysians accounting for half of the marine landed catches (DoF, 1997). Recently, the concentrations of Cd, Cu, Pb and Zn in the sediments were reported for the west coast of Peninsular Malaysia (Yap et al., 2002a, 2003). These studies further strengthened the importance of the west coast from an ecotoxicological point of view. Malaysians are also dependent on river systems for fresh water for drinking and washing, as well as for industrial use, and as a source of freshwater fish and prawns for food. Besides that, mangrove swamps and other wetlands are the breeding grounds for fish, prawns and crabs besides being the habitats of migratory birds. The few natural freshwater lakes, as well as dams, are sources of fish and prawns. The islands, lakes, dams and beaches are popular as recreational destinations for both local as well as foreign tourists, and the landing of turtles on the pristine beaches is a major attraction for visitors. Hence it is imperative for Malaysia to be able to systematically and efficiently monitor the health of her aquatic ecosystems, not only in terms of the levels of pollutants pouring into them, but also in terms of the state of richness of species diversity living in them. As far as the application of biochemical and molecular markers in the assessment of Malaysia's aquatic ecosystems is concerned, they have been mainly used to characterize potentially rich resources of genetic and phenotypic diversities, although a start has been made to use them to trace pollution sources and levels.

Characterization of bioresources

The Malaysian aquatic ecosystems which are the sources of a significant proportion of the nation's food through both marine capture fisheries and aquaculture, play prominent roles in the nation's economy. In 1997 they contributed 1.6% of the gross domestic product and provided employment to about 80,000 fishermen and 20,000 fish culturalists (DoF, 1997). Annually approximately 1,400,000 metric tones (mt) of fishery derived animals are landed in Malaysia, of which about 1,100,000 mt would be derived from marine fishery and the rest from freshwater (SEAFDEC, 1997). The main marine fishes landed are given in Table 1.

In addition, 318,695 mt of trash fish of various species were also landed. Of the 103,685 mt of marine crustaceans landed: 22,250 mt were penaeid prawns, (udang puteh, udang kaki merah and udang susu), Penaeus merguiensis/P. indicus/P. latisulcatus; 634 mt were tiger prawns (udang harimau), Penaeus monodon/P. semisulcatus; 69,902 mt were of other types of prawns of various species; 702 mt were of spiny lobster (udang karang), Panulirus polyhagus; and 10,197 mt were of swimming crab (ketam laut), Portunus pelagicus. Among the 63,724 mt of mollusks landed: 15,476 mt were squids (sotong biasa), Loligo spp.; 15,475 mt were cuttlefish (sotong katak), Sepia spp.; and 15,982 mt were of other types of mollusks. In addition, 7,692 mt of jellyfish (ubur-ubur), Rhopilema spp., were also landed but no significant quantity of aquatic plants, for example seaweeds, was harvested from the sea.

Mariculture activities occupied 4,767 hectares (ha) of space and yielded 101,080 mt consisting mainly of blood cockle (kerang) (Table 2). The other animals maricultured included the blood cockle, green-lipped and green sea mussels, and the flat and rock oysters. Brackish water culture occupied 2,695 ha and involved 2,192 establishments with a yield of 13,169 mt consisting mainly of tiger prawn, barramundi (siakap), various types of marine fish, and mangrove crab.

Freshwater culture involved 15,659 establishments covering 6,537 ha with a total yield of 18,493 mt. As indicated in Table 2, the main fish cultured are tilapia, various types of carps, eel, which were cultured in a large farm of about 2,000 ha in Pahang, catfish, snakehead and miscellaneous other freshwater fish. Additionally 79 mt of the giant freshwater prawn, Macrobrachium rosenbergii, were also produced.

According to the Malaysian Department of Fisheries the per capita consumption of fish in Malaysia is 35 kg (about 60–70% of protein consumption) and fish is a food acceptable to all ethnic groups in this country except for vegetarians. Thus, aquatic resources should form an important basis for Malaysia's food security. The Government of Malaysia under the Malaysia Incorporated Concept is committed to the development of the fishing industry; be it capture fisheries or aquaculture, on a modern, commercialized basis involving the corporate sector and entrepreneurs. At the same time, it aims to ensure that the fisheries resources are sustainable in the long term and that aquaculture does not degrade the environment or cause deterioration in the water quality of the coastal areas (Mohd. Mazlan, 1997). Under the Malaysian National Agriculture Policy announced by the Minister of Agriculture in January 1999, the need for sustainable development of the fishery industry was emphasized. However, the Malaysian fishery industry is mainly dependent on marine capture for the supply of food. Currently the seas around Malaysia have already reached their potential exploitable fish resources. The growth in marine capture fisheries was 4.4% during the 1990–1995 6th Malaysia Plan whereas its targeted growth is only 1.2% during the current (1996–2000) 7th Malaysia Plan period. As an alternative, the development of Malaysia's own deep-sea fishing fleet had been suggested to overcome the present reliance on the coastal fishing industry (Mohd. Mazlan, 1997). However, even globally there is little prospect for further significant increases in fish production through marine capture fisheries (Knauss, 1997; Musick, 1999). This leaves aquaculture, both marine and land-based, as the only viable alternative for Malaysia to increase food production through the resources found in her extensive aquatic ecosystems. As both overfishing and aquaculture impact greatly on the natural aquatic environment, such activities should be monitored closely and effectively by the relevant regulatory authorities to prevent any adverse consequences from arising.

In order to do this, knowledge of the biological resources present in the aquatic ecosystems of Malaysia is essential and must be carried out using a multi-pronged approach which includes taxonomic, ecotoxicological and genetic studies. Genetic information is essential to understand the breeding structures of species, populations and stocks so that they can be managed and utilized sustainably, as well as to ascertain the long term effects of any environmental changes such as those that could be brought about by a major oil spill or the continued discharge of industrial and agricultural effluent into waterways and seas. Unfortunately, very little is now known about the genetic structures of the organisms living in aquatic ecosystems, especially in the sea. Currently, efficient techniques such as typing for biochemical markers at the protein level and molecular markers at the DNA level are available (Ferguson, 1994). Therefore, genetic surveys such as investigations on the genetic structures of a morphologically similar biomonitoring agent collected from different geographical areas and environmental backgrounds, are important to know the level of genetic differentiation due to environmental factors such as pollution. This information will greatly complement the ecotoxicological studies using the same biomonitoring species. In view of that, such genetic studies (biochemical/molecular markers) should be done in line with ecotoxicological studies, before further environmental changes (especially due to pollution) occur in the aquatic ecosystem.

Tan (1994) identified the sources of fish seed supply for aquaculture in Malaysia as being from local hatcheries, from the wild or from imports. The local hatcheries produce seeds of tilapia, Javanese carp, big head carp, common carp, catfish and seabass. For cockles, mussels, grouper and snapper the seeds are collected from the wild. It is imperative that the genetic diversity of the wild populations and the culture stocks be ascertained by the use of biochemical and molecular markers. This is because morphological markers usually cannot distinguish between populations and stocks within species or even between closely related species. Choices of stocks to be used in crosses should ideally be made with the knowledge of genetic distances calculated from gene frequency data of biochemical and molecular loci since stocks differ to varying degrees and are not all equally suitable for breeding programmes (Ferguson, 1994). Moreover, it is equally important to monitor the heterozygosity levels of the breeding stocks at every generation of aquaculture to prevent the appearance of the deleterious effects of inbreeding which can manifest themselves in economically important characters such as lowered resistances to diseases, slower growth and decreased survival rates. Such occurrences are common in the aquaculture industry such as in shrimp culture, which often undergoes cycles of boom and burst (Guo, 2000). For the same reasons it is even more important that the heterozygosity levels of the wild populations be maintained in order to prevent them from becoming extinct due to overexploitation by man, threats from environmental degradation, diseases and competition from the accidental release into the environment of exotic species imported by aquaculturalists. The genetic relationship between any two populations is a function of differences between them in allelic frequencies with this relationship usually expressed as a genetic distance (Nei, 1978). For good estimates of genetic relationships, Barker et al. (1997a, 1997b) recommended the use of at least 20 polymorphic loci.

Current status

Most of the biochemical and molecular genetic studies that have been done in Malaysia had been on freshwater aquacultured fish and marine and freshwater prawns. Patimah et al. (1989) and Daud et al. (1989) used between 15–18 allozyme loci to characterize the catfishes, Clarias macrocephalus, C. batrachus, Mystus nemurus and Prophagorus cataractus. Twenty-five allozyme loci were used to define the genetic relationships among seven local wild and hatchery populations of M. nemurus (Siraj et al., 1998a). Fewer loci, 3–6, were used by Tan et al. (1980) to study snakeskin gouramy (sepat Siam) Trichogaster pectoralis and by Mohd. Azlan (1985) and Halmy (1985) to study blood cockles. Yuzine (1996) used 32 and 35 allozyme loci respectively to study Penaeus merguiensis and Macrobrachium rosenbergi (udang galah) populations and brood stocks. Allozyme loci had been used for temporal studies in guppies, Poecilia reticulata (Yao, 1980; Hasnah, 1982; Surinderpal, 1984) and the edible aquatic snails introduced from South America Pomacea insularis and P. canaliculata (Nadirah, 1993; Chan, 1999) which are now major pests of paddy in Malaysia. Nadirah (1993) also did population studies on the indigenous aquatic snails, Pila scutata, P. pesmei and P. spp., using allozymes.

DNA level markers had been used to study the Malaysia's aquatic organisms since 1997. Tilapia had been studied using both 32 allozyme loci (Selvaraj et al., 1994) and 11 DNA microsatellite loci (Bhassu et al., 1999). Although tilapia originated in Africa, since its introduction to Malaysia in the early 1940s it has been extensively aquacultured and escapees from the culture ponds have now established themselves ubiquitously in the freshwater bodies of Malaysia. These feral fishes are usually O. mossambicus or O. niloticus or hybrids or backcrosses among themselves. Daud et al. (1997) used mitochondrial DNA restriction fragment length polymorphism (RFLP) to study six Malaysian Penaeus monodon populations and allozymes (Daud et al., 1995) to discriminate between P. monodon and P. merguiensis while Siraj et al. (1998b) had DNA fingerprinted the Javanese carp and Asma et al. (1998) used 73 random amplified polymorphic DNA (RAPD) markers in their study of three local strains of the ornamental fish tiger barb, Puntius tazona. Groupers (Epinephelus spp.) from the Straits of Malacca were typed using RAPD markers by Daud et al. (2000). The marine dinoflagellate, Ostreopsis ovata, found in coral reefs and seaweed beds in Malaysia may produce toxins that contribute to ciguatera fish poisoning. Using rRNA gene sequencing, Leaw et al. (2001) were able to not only distinguish genetically between two species O. ovata and O. lenticularis but also between two distinct strains of O. ovata; those from the Straits of Malacca (isolates from Port Dickson) and those from the South China Sea (isolates from Pulau Redang off the east coast of Peninsular Malaysia and from Kota Kinabalu on the island of Borneo).

The river catfish Mystus nemurus is widely distributed in both mainland as well as archipelago Southeast Asia. Due to its good flesh quality, it is a popular freshwater food fish throughout the region and is therefore of interest to aquaculturists. In order to complement the information obtained through the use of protein level polymorphic markers, 42 random amplified polymorphic DNA (RAPD) and 158 amplified fragment length polymorphism (AFLP) markers were used to increase the number of molecular markers available to type this fish from populations obtained from Perak, Kedah, Johor, Selangor and Sarawak. Both types of markers revealed high genetic diversities within the Selangor and Sarawak populations and a low level in the Kedah population. The low level in the Kedah population may be an indication of overfishing while the high level in the Selangor population is in accordance with the fact that this hatchery population in Universiti Putra Malaysia was established by using fish obtained from different geographical areas. In order to get an idea of the genetic relationships among the populations based on RAPD and AFLP data respectively, an Unweighted Pair Group Method with Arithmetic Averaging (UPGMA) dendrogram was generated based on the similarity matrices (Nei and Li, 1979) for each of the two DNA typing techniques used. In both dendrograms, the four populations from Peninsular Malaysia clustered together whereas the Sarawak population from Borneo Island clustered by itself (Chong et al., 2000). These dominant markers are excellent for genetic characterization of populations and it can be expected that hybrid vigour in crosses between Sarawak and Peninsula fish will be found, but they are not efficient for testing for possible associations between quantitative traits of economic importance such as growth rates, disease resistance and molecular markers. Therefore several approaches were used including Random Amplified Hybridisation Microsatellites (RAHM) (Cifarelli et al., 1995) and Direct Amplification of Length Polymorphisms (DALP) (Desmarais et al., 1998) in order to obtain codominant DNA microsatellite markers for this species. We have identified more than fifty such microsatellite loci and are in the process of testing them for polymorphisms in the local populations.

In the realm of marine organisms, two of the four species of turtles that land on Malaysia's beaches namely the hawksbill turtle, Eretmochelys imbricata, and the green turtle, Chelonis mydas, had been studied. Tan et al. (2000) using RAPD markers to study hawksbill turtles found that the Sabah population was distinct from the peninsular populations from east Johor and Melaka. Joseph (2001) through the use of 14 DNA microsatellite loci confirmed the distinctiveness of the Sabah population from the peninsular ones from Melaka, Johor and Terengganu. The Johor and Terengganu populations from the peninsular east coast were also distinct from the west coast Melaka population. Similar studies by her also using 14 microsatellite loci on green turtle populations from Pahang, Terengganu, Perak, Sabah and Sarawak revealed that the peninsular east coast, west coast, Sarawak and Sabah populations are distinct from one another and conservation measures must be strictly enforced in each area so that these endangered animals will not become extinct. Traditionally, turtles have commercial value as sources of eggs, meat and shells and the green turtle is especially popular for preparing turtle soup. However, since marine turtles are mainly endangered now, commercial exploitation of these animals should be strictly curbed. Perhaps some day in the future should current conservation measures be successful in increasing the turtle populations worldwide, one may be able to once again enjoy turtle steak, soup and eggs.

Biochemical and molecular markers and pollution levels and sources

Gillespie and Guttman (1999), based on evidence from research in aquatic toxicology which they reviewed, proposed that allozyme analysis can be a useful tool for estimating the effects of environmental chemicals on genetic variation in natural populations. Associations had been found between exposure to environmental toxicants with changes in allozyme variation in natural populations of many species. However, the trend of the change is not consistent. Some studies, for example those of Fore et al. (1995a) on the stoneroller minnow, Campostoma anomalum, and DeMarais et al. (1993) on the river chub, Gila seminuda, found that the genetic heterozygosity levels increased with exposure to environmental pollutants. Others like those of Fore et al. (1995b) on the blunt nose minnow, Pimephales notatus,Benton et al. (1994) on the mosquitofish, Gambusia holbrooki, and Koop et al. (1992) on the central mud minnow, Umbra limi, showed just the reverse. In studies of natural populations from the field however, it is difficult to prove conclusively that chemical pollutants are the only causes of the changes in genetic variation. Factors such as the exact local conditions, the genetic structure of the species being studied, as well as genetic drift and gene flow dynamics (Avise, 1994) can also cause differences in allozyme gene frequencies.

In order to control some of the variables found in field studies, laboratory studies had been done during which animals were exposed to chemical toxicants to determine the relationship between allozyme variation and various pollutants. Again the results had been ambiguous. Nevo et al. (1986) studied three pairs of species belonging to three genera and families of marine gastropods, Monodonta turbinate and M. turbiformis, Littorina punctata and L. neritoides, and Cerithium scabridum and C. rupestre, which were exposed to heavy metals (lead, copper, zinc, mercury and cadmium), detergents and crude oil, and found that in all three cases the species with a higher degree of genetic diversity was more resistant to all pollutants than its counterpart. Both Diamond et al. (1989) and Benton and Guttman (1992) who studied the effects of mercury exposure on Gambusia affinis and Nectopsyche albida, respectively, found increased tolerance to be positively correlated with allozyme genotype heterozygosity. This is in contrast to the result of Mulvey et al. (1995) who studied exposure of mercury to Gambusia holbrooki, but found no relationship between tolerance and allozyme heterozygosity, and that of Newman et al. (1989) who found that for arsenic exposed Gambusia affinis, increased tolerance was negatively correlated with heterozygosity in the males. In the mussel, Mytilus edulis, Beaumont and Toro (1996) tested for allozyme heterozygosity levels in animals exposed in the laboratory to copper toxicity or starvation. They found that among the survivors of copper toxicity there were a greater proportion of heterozygotes, whereas among the survivors of starvation, there was no such association. Of the many allozyme loci that had been studied, phosphoglucomutase (Pgm), glucose phosphate isomerase (Gpi) and malate dehydrogenase (Mdh) had been most often associated with correlations between environmental pollutants and allozyme frequency changes in both field and laboratory based studies. However, the reasons for the involvement of these loci is still unclear (Gillespie and Guttman, 1999) although many plausible hypotheses had been suggested such as differential inhibition of different allozymes by specific chemicals (Kramer and Newman, 1994), differential metabolic responses by different allozyme genotypes (Kramer et al., 1992) or that they may be closely linked to other loci that confer resistance to pollutants.

In Malaysia, the use of enzyme polymorphisms to study responses of aquatic organisms (or any organism for that matter) to environmental pollutants is just beginning. The green-lipped mussel, Perna viridis, is a local seafood delicacy besides being a potential biomonitoring agent of pollution levels as part of the worldwide Mussel Watch program. However, before it can be used as a valid biomonitoring agent the population genetic structure of this species in the straits must be known. Yap et al. (2002b) used 14 allozyme loci to study populations of the green-lipped mussel from eight locations in the Straits of Malacca. He found that the two northern populations from Penang were distinct from the other six populations from the central and southern parts of the straits but the Nei's genetic distance values (Nei, 1978) were within the range for conspecific populations. This allows P. viridis to be used as a biomonitoring agent for pollution levels in the Straits of Malacca. Subsequently, Yap et al. (2004) compared the metal pollution indices (MPI) based on the levels of copper, zinc, lead, cadmium and mercury in the habitat sediment as well as the soft tissues of P. viridis from four geographical locations from the central and southern parts of the Straits of Malacca namely Bagan Lalang, Pantai Lido, Tanjung Kupang and Kampung Pasir Puteh with values of the percentage of polymorphic loci (P) and mean heterozygosity (H) based on 14 allozyme loci. They found that the mussel population from Kampung Pasir Puteh, the location with the highest MPI for both sediment and tissue, had the highest P and H values also indicating that mussels living in the polluted area had greater genetic heterogeneity. Such studies should be expanded upon to include other environmental pollutants, molecular markers and laboratory based investigations as well as extended to other potential bioindicator organisms such as the freshwater snail, Brotia costula (Toy, 2001).

Zakaria et al. (2000) proposed the use of pentacyclic triterpanes (C29/C30 and C31-35/C30 ratios) as a molecular biomarker to identify the source of tar-ball as a pollutant in the Straits of Malacca in the event of an oil spill. This is because Southeast Asian oil and West Asian oil have different characteristic ratios. Unfortunately, this technique cannot be used to trace the origin of contamination by oil of sediment and mussel because the lubrication oil used in Malaysia is of West Asian origin.

Further applications of biochemical and molecular indicators in the study of the Malaysian aquatic ecosystems

Local genetic diversity information is not available for the ten major types of marine fish landed in Malaysia; namely Indian mackerel, round scad, selar scad, sardine, threadfin bream, longtail tuna, anchovy, hard tail scad, drum and croaker and ray. Genetic diversity studies have not yet been done on the other two species of turtles that land on Malaysian beaches; namely the leatherback turtle, Demochelys coriacea and the olive ridley, Lepidochelys olivacea. The painted terrapin, Callagur borneonsis, also lays eggs on these beaches. It is not a marine turtle as it lives in rivers and estuaries and swims out to coastal waters only during the nesting period. No genetic study has been done on this turtle either. Other bioresources that should be studied include aquatic micro-organisms, seagrasses, crabs and corals which are all important to the Malaysian aquatic ecosystem, as well as being of economic value for the biotechnology as well as tourism industries. Therefore, genetic studies using both biochemical and molecular markers should be done on them as a matter of priority.

Besides the biochemical and molecular techniques that have been discussed above, many others are available that could also be utilized to study Malaysia's aquatic ecosystems (Huggett et al., 1992). These could be used to determine the effects of stresses such as chemicals, metals and other pollutants, as well as temperature and other changes in the environment on living organisms. At the biochemical level, exposure to pollutants can lead to changes in a number of enzymes and other proteins, which are involved in the specific responses of organisms to toxic chemicals. In numerous cases, these responses are adaptive but they can also lead to toxic effects. Enzyme assays can be done using various substrates to ascertain the rate of conversion of the substrate to the final product. Among the systems (Stegeman et al., 1992) known to be involved in the responses that could be used as potential biomarkers are cytochrome P450 monooxygenases, metallothioneins, stress and heat shock proteins, phase II (conjugating) enzymes, antioxidant enzymes and the heme and porphyrin biosynthetic pathway.

At the DNA level, exposure of an organism to a genotoxic compound could lead to a series of events such as structural alterations to the DNA, processing of this damage and production of mutant genes could lead to a disease or genetic defect. The detection and quantification of these events may be used as molecular markers to determine the exposure of organisms to environmental contaminants and their effects (Shugart et al., 1992). Among the events that could be detected are the formation of DNA adducts, secondary modifications, strand breaks, minor nucleoside content, unscheduled DNA synthesis which in turn could lead to irreversible events such as cytogenetic effects and mutations. Mutations effects that could be detected include oncogene activation and increases in mutation rates. The presence of environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs) or chlorinated hydrocarbons can induce tumours in fish (Baumann et al., 1982). The ras gene family (McMahon et al., 1990) is involved in oncogene activation. While no such molecular level study had been done before in Malaysia, Shariff (2001, personal communication, M. Shariff, Faculty of Veterinary Medicine, Universiti Putra Malaysia, Serdang, Malaysia) has recently initiated a project to identify, isolate and sequence the homology of the ras gene among Malaysian flatfish and to subsequently compare the expression of this gene in those fish obtained from polluted and unpolluted sites along the Straits of Malacca, define the pollutant concentration that causes ras point mutations which could be used as bioindicators of pollution and determine the protein expression of this gene as an early health screen for pollution.

Conclusions

Numerous biochemical and molecular tools are currently available to study Malaysia's varied aquatic ecosystems, but their usage is just beginning. They can be utilized to elucidate the genetic structures of Malaysia's rich bioresources and biodiversity, to trace sources of origins of pollutants, as well as to study the biochemical and molecular effects of pollutants on biomonitoring organisms from the ecotoxicological point of view. It is, therefore, possible that biochemical and molecular markers could be used for monitoring aquatic environmental health, in terms of water pollution and eutrophication, for example. The potential diagnostic (both biochemical and molecular) markers are of relevance in detecting any potential toxicological effects in the biomonitoring organisms due to environmental pollution. Therefore, future studies utilizing biochemical/molecular genetics should be merged with ecotoxicological studies so that a better foundation for the use of biochemical and molecular indicators of environmental pollution in the aquatic ecosystem could be obtained. The problems facing Malaysia's aquatic ecosystems are now urgent, but what is limiting are the numbers of researchers and the research funding available to study them.

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