Genetic manipulation in farmed fish: enhancing aquaculture production

Ever since the creation of human civilisation, breeding has been the pivotal struggles to increase and diversify agricultural production, enhance food security and incomes, and adapt farming to changing environmental conditions and social needs. This is achieved by exploiting variation of the plant and animal genetic resources’ traits. These preferred genetic materials are improved through selection and reproduction and this practice remains the basis for producing new generations of domesticated and indigenous breeds. Aquatic organisms particularly finfish and shellfish that are cultured today originated largely from the introduction of scientific breeding at the beginning of the twentieth century. Inclusion of crosses into breeding schemes prior to artificial selection and application of Mendel’s laws of inheritance to improve both simple and quantitative traits follows. For effective breeding effort, selecting genetic materials with one or a combination of the required traits still relies mainly on physical features (phenotype) which are influenced by the environment thus could be misguided to the actual heritable genetic composition (genotype) of the material being considered. The extent of aquatic diversity is both extremely large and relatively poorly understood. Thus, identification, selection and estimation of specific traits (such as growth rate, disease resistance) in wild and cultured fish and shellfish through genetic tools and breeding programmes are a must to secure future improvements in genetic resources for food. Ever since the discovering of DNA structure over 50 years ago, scientists have made tremendous strides in identifying genes and gene functions, making it increasingly possible to detect genetic differences (DNA polymorphisms) for traits among individuals in a much more direct way, thereby assisting in the selection of desired traits. In fish, manipulation of the pre-embryonic stages rendering different ploidy levels is achievable and tolerable. Triploid fish is produced through various physical, chemical and biological stimulants. Triploids generally cannot reproduce, so the energy that is not channelled into reproduction would go instead to increasing growth rate. Induction of gynogenesis involves egg activation by irradiated homologous or heterologous sperm, and diploidization by retention of the second polar body (meiotic gynogenesis), or suppression of the first mitotic cleavage (mitotic gynogenesis). As a consequence, these gynogens are “instantly inbred” and can be screened for phenotypes quickly to avoid the generations of breeding necessary in a conventional manner. Artificial breeding is a simple genetic technology for forced reproduction such as the use of pituitary gland extract and other hormones to initiate gamete development and induce spawning (the release of fish eggs) besides triggering factors of the environment

Length-weight relationships of seven catfish species in Peninsular Malaysia.

The study described the Length-Weight Relationship (LWR) of commercially important and indigenous freshwater catfishes from Peninsular Malaysia. Seven species of freshwater catfishes from three families (Bagriidae, Clariidae and Pangasidae) were collected from various rivers in Peninsular Malaysia. Allometric coefficient, b in LWR varied between 2.19 and 3.20. The LWR with high correlation coefficient (r2) is significant for all species except P. nasutus. The present study also documented first reference for Pangasius nasutus and Pseudomystus siamensis

Growth performance and gonad development in Diploid and Triploid Clarias batrachus (Linnaeus)

Full siblings of diploid and triploid walking catfish, Clarias batrachus, were reared in rectangular fibreglass tanks starting at the age of three weeks. Growth performances of diploids and triploids were compared by feeding with a 30% protein diet. At the end of the study period growth rate was found to be insignificantly different (P>0.05) between the diploid and the triploid. However, triploid fish had poorly developed gonads. Triploid ovaries contained fewer primary oocytes with some abnormal maturing oocytes. Triploid testes contained fewer seminiferous tubules and a larger amount of connective tissue

Cross-species amplification of microsatellite DNA markers and comparison on the sequence of microsatellite regions among Southeast Asian Catfish species

Thirty microsatellite markers developed for River catfish (Hemibagrus nemurus) were screened for cross amplification in six species of catfish. Out of 30 primers, only 3 (10) to 6 (20) produced successful amplifications in six catfish species. Six different loci could be amplified in Pangasius pangasius and Clarias batrachus, 5 loci in Clarias gariepinus, 4 loci in Pseudomystus siamensis and 3 loci in Clarias macrocephalus and Pangasius nasutus. The low rate of amplification in these 6 closely related species proved the primers are locus-specific. Sequence analysis of locus MnRm7-1 showed differences in the flanking region and repeat motif in certain species, suggesting the existence of indel mutations in catfish species in that particular region. The examined DNA sequence revealed that the repeat motif is conser ved within Pangasiid catfishes and not conser ved within Clariid catfishe

Cross species amplification of ikan kelah, Tor tambroides by using Mystus nemurus microsatellite markers

Thirty eight microsatellite markers developed from a Random Hybridising Microsatellite (RAMs) enrichment protocol created from the DNA of the river catfish, ikan baung, Mystus nemurus were screened to cross amplify ikan kelah, Tor tambroides . Only five primers which amplified bands at the expected allele size regions were used for characterizing this species. The observed heterozygosity values were higher than the expected heterozygosity values for the bands amplified by primer pairs MnSC4-3B, MnLR2-1-52A and MnRmC3-1 across the three populations but the bands amplified by primer pairs MnSC4-1A and MnLR2-1-17B showed lower observed heterozygosity values than the expected heterozygosity values. The mean FIS value across the three populations was negative, indicating no deficit in heterozygosity. The mean value of FST was low indicating no gene was fixed within populations relative to the total population. The high value of Nm suggested high gene flow among the three populations. Both the (x2) chi-square and the (G2) likelihood ratio tests showed significant differences (P<0.05), indicating deviations from Hardy-Weinberg equilibrium in most loci except for one locus (MnSC4-1A) in the Negeri Sembilan population and two loci (MnLR2-1-52A and MnSC4-1A) in the Kelantan population. The genetic distance values generated ranged from 0.1053 to 0.1960. The UPGMA dendrograms constructed from the genetic distances based on the microsatellite markers showed that the Negeri Sembilan and Kelantan populations shared a similar cluster while the Pahang population was on its own

Intraspecific polymorphism in mystus nemurus (C&V) detected by RAPD-PCR fingerprinting

Yellow catfish, Mystus nemurus (C&V), is becoming one of the majorfreshwater species farmed l7y aquaculturists in Southeast Asia. It was of interest to examine levels of genetic sub-population differentiation among samples of this species obtained from parts of its range, as well as to compare the genetics of wild and hatchery-bred fish. The genetic aspects of variation in the fish, which were collected from eight wild populations throughout Thailand and a hatchery stock, were determined at molecular (DNA) level using the technique ofRAPD-PCRfingerprinting. Five arbitrary primers namely OPA-11, OPA-14, OPA-18, OPA-19 and OPA-20 were chosen to amplify products, which showed 28 polymorphic loci in 9 populations. The highest genetic distance (D) was found between Chainat and Suratthani populations with the value of 0.289, while the lowest was found in Songkhla population and hatchery stock with the value of 0.087. The dendrogram depicts the genetic relationship among populations of M. nemurus, which are grouped into four clusters according to their regional areas

Effects of Packing Densities in Plastic Bags on Survival of Larvae and Fry of Helostoma temmincki (C&V)

Helostoma temmincki (C&V) larvae measuring 4.6 ± 0.6 mm total length were packed in plastic bags with oxygen at stocking densities of 0, 250, 500, 1000 and 1500/liter. Fry measuring 2. 0 cm ± 0.2 were similarly packed at densities of 0, 125, 250, 500 and 750/litre. The fish were observed for mortality 10 minutes, 24 hours and 48 hours after packing. The water quality parameters - temperature, dissolved oxygen, ammonia-N, dissolved carbon dioxide, pH and alkalinity - were determined at 0 hours for control bags only and for all bags at 48 hours after packing. There was no mortality in all bags 10 minutes after packing. After 24 hours, mortality of larvae packed at 500, 1000 and 1500/litre was less than 2% whereas no mortality was observed in the bags with fry. At 48 hours, mortalities of larvae were similar (P > 0.05) in all bags and were less than 2%. Mortalities of fry packed at 125, 250 and 500/litre were similar (P> 0.05) and less than 2%, whereas mortality of fry packed at 750/litre was significantly different (P < 0.05)

Morphometric analysis of Malaysian Oxudercine goby, Boleophthalmus boddarti (Pallas, 1770)

The Oxudercine gobies or mudskippers are locally known as belacak or "tembakul". These euryhaline fish are amongst the air breathing gobies found in Malaysia. Boleophthalmus boddarti is one of the common mudskippers inhabiting tidal flats, mangrove swamps, estuarines and coastal areas. Conventional and truss morphometrics as well as meristic data from 85 samples in five populations (Pulau Pinang, Kuala Selangor, Banting, Port Dickson and Melaka) of B. boddartiwere analyzed using one-way ANOVA and Principal Component Analysis (PCA). Fifteen morphometric, 28 truss morphometric and 9 meristic data were analyzed to examine the degree of similarity among the five populations. All morphometric characters within and between the populations were significantly different (P< 0.05). Using the conventional morphometric data analysed by PCA, the populations of B. boddarti are clustered into 3 groups, where Banting andMelaka populations form the first group, Pulau Pinang and Kuala Selangor populations the second group and Port Dickson population the third group. In contrast, 3 groups were also clustered based on the truss morphometric data but the grouping was different. The three groups from the truss morphometric data consist of Kuala Selangor and Banting populations in the first group, Melaka and Port Dickson populations the second group and the Pulau Pinang populationthe third group which is distantly separated from the other two groups. The results indicate that the shape of mudskippers in the northern part is distinct from the middle and southern parts of Peninsular Malaysia. Based on meristic data, all populations were centric and no grouping was identified. The length-weight relationship for B. boddarti in this study was described as log W=log 0.754 + 1.029 log TL

Mitochondrial DNA diversity of Tar douronensis valenciennes(Cyprinidae in Malaysian Borneo.

This study examines the population structure and taxonomy of Tor douronensis, an important indigenous freshwater fish species in Malaysian Borneo, by using sequence analysis of 466 base pairs of the mitochondrial cytochrome c oxidase I (COl) gene. A total of 62 fish samples were collected from five locations in Sarawak (N=54) and Sabah (N=8). The phylogenetic analysis using the Neighbour Joining (N]) method supported the monophyletic status between T. douronensis and Tor tambroides, which further reinforced their taxonomic status as distinct species. The T. douronensis haplo types were further divided into three major groups, with the Pelianuh from Sabah forming its own group (Cluster Ill) with strong bootstrap support. The large genetic differences separating the Sabah haplotypes from its Sarawak congeners suggested that the Pelian fish might represent a cryptic species. The current study showed high levels of intra and inter-population variations in T. douronensis. Within all population variations, T. douronensis populations were found, except in Bario. The presence offixed haplotype differences along with high FST values among the populations of T. douronensis, support the conclusion that little or no migration occurred among the extant populations separated by large geographic distances or river systems. However, the sharing of haplotypes between some such populations, for example between Batang Ai and Bario (HS6), and between Batang Ai and Ulu Limbang/Ba Kelalan (HS2) provided support that T. douronensis had a historically widespread natural distribution in the region probably during the Quaternary period. Overall, the present study was able to shed light on the taxonomy and population structure of T. douronensis in Malaysian Borneo