Effects of silver carp and the small indigenous fish mola Amblypharyngodon mola and punti Puntius sophore on fish polyculture production

A sustainable semi-intensive pond aquaculture technology including major carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. The inclusion of silver carp (Hypophthalmichthys molitrix), a cheap large species affordable by poor farmers, is now being considered. As part of a study on the effects of this filter feeder on polycultures including the large carps rohu (Labeo rohita), catla (Catla catla) and common carp (Cyprinus carpio) and the SIS punti (Puntius sophore) and mola (Amblypharyngodon mola), an experiment was carried out under farm conditions to test the effects of silver carp and of each SIS species on the growth, survival and yield of the large and small species and on pond ecology.The experiment was performed in 38 farmers' fishponds of different sizes, from 220 m² to 1200 m². The results show that the larger the fish pond the better rohu performance, the larger punti fry weight and the lower punti fry harvested biomass. Pond size did not affect other fish species. The addition of 250 mola and/or punti per 100 m² fishponds affected rohu and catla and did not affect common and silver carps. The addition of mola alone reduced rohu's parameters by 15%. The addition of SIS in the three combinations tested (250 mola, 250 punti, 125 of each species) reduced catla's parameters by 20-24%. Punti fry were larger when both SIS were stocked and punti fry biomass was larger when only punti were present. Total mola harvested biomass and yield were larger when the entire SIS stocked were only mola.The addition of 10 silver carp over the 99 large carps stocked per 100 m² fishponds negatively affected rohu and catla growth and yield by about 15-21% and 45-50% respectively but not their survival, did not affect common carp performance, did not affect punti and mola reproduction in the ponds, reduced punti yields by 25%, reduced mola performance by about 35%, and silver carp own biomass increased total yield and total income in about 12% each. These effects are explained and discussed considering fish interactions through the food web. The decreased income from selling the more expensive large carps is more than compensated by that obtained from silver carp, which allows the option to the farmer to sell part of the silver carp to complete the cash income that would have been obtained from large carps only if silver carp would not be stocked, and consume the rest with the family.     

Decreased genetic diversity and a reduced effective population size in cultured silver-lipped pearl oysters (Pinctada maxima)

Before selection programmes for aquaculture species can commence, a fundamental knowledge of how the culture process affects genetic diversity is requisite. “South Sea” pearl production, through the culture of the silver-lipped pearl oyster, Pinctada maxima, stands to gain substantially from genetic selection. Aquaculture techniques for P. maxima have progressed vastly, to a point where the majority of current operations are based on hatchery-propagated stock; however, there has been no investigation on how the culture process is affecting the genetic diversity of this species. To address this deficiency, we investigated the genetic diversity and effective population sizes (N_e) in three wild and five hatchery-produced P. maxima populations. Using six microsatellite DNA markers, cultured populations exhibited low N_e (3.5–9.2) and reduced allelic richness (29–44%) compared with their wild progenitors. Observed heterozygosities were not affected greatly, however, an increased mean pairwise genetic relatedness was observed in all cultured populations. The practice of mass spawning was identified as a major factor in the reduction of diversity, although diversity was not necessarily maintained when a more controlled spawning approach was utilised. Pedigree reconstructions revealed genetic diversity and N_e is affected by large skews in full-sib family representations (up to 40% from a single family, in a cohort using 28 broodstock), and could be due to differential survival rates amongst communally reared families. In order to maximise future selective breeding efforts, further research should be directed towards identifying critical stages of the culture process in which genetic diversity is lost.     

Improving breed-and-release programmes in the face of a threatening pathogen,Batrachochytrium dendrobatidis

1. As the proportion of threatened species increases, so too does the need for effective conservation strategies. In response, captive breed-and-release and habitat mitigation programmes are two conservation actions that are increasing in use and effectiveness.
2. Success of these programmes is frequently hampered by the continued presence of threatening processes. In the case of amphibian reintroductions, a key threatening process that is difficult to eliminate is the deadly fungal pathogen, Batrachochytrium dendrobatidis (Bd). This pathogen is the proximate cause of decline for the threatened green and golden bell frog, Litoria aurea, and has contributed to the failure of previous breed-and-release programmes of this amphibian.
3. To investigate whether is it possible to establish a captive-bred population of L. aurea that could persist in the presence of Bd, a breed-and-release programme was conducted in a created habitat that included increased salinity to inhibit fungal growth rates, exclusion of potential reservoir hosts and source animals bred from parents ‘experienced’ with the strain of Bd present in the release environment.
4. The population persisted in the created habitat for more than 4 years (the timescale of monitoring) but suffered higher infection levels compared with nearby extant populations of L. aurea. These infections significantly reduced apparent survival. Infection dynamics were linked to temperature, host density in the previous season, and size and age of the host, and these factors differed from those in extant populations and are likely to have contributed to the high levels of Bd infection at the created site.
5. This article discusses how it may be possible to manipulate these factors to improve the success of future breed-and-release programmes, and recommends the construction of warm water bodies and a strategy of prioritizing the release of fewer, large propagules of high body condition and mixed-age class, over large numbers of younger, smaller animals.

     

Effects of silver carp and small indigenous species on pond ecology and carp polycultures in Bangladesh

A sustainable semi-intensive pond aquaculture technology including major carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. The inclusion of silver carp (Hypophthalmichthys molitrix), a cheap large species affordable by poor farmers, is now being considered. As part of a study on the effects of this filter feeder on polycultures including the large carps rohu (Labeo rohita), catla (Catla catla) and common carp (Cyprinus carpio) and the SIS punti (Puntius sophore) and mola (Amblypharyngodon mola), an experiment was carried out to test the effects of silver carp and of each SIS species on the growth, survival and yield of the large and small fish and on pond ecology.The ecology of the ponds was dominated by changes in time, strongly related to the development of a surface plankton scum at the beginning of the culture season and weather conditions. The surface scum increased decomposition processes and decreased algal development in the water body, promoted photosynthesis and ammonium release and reduced nitrification. Over those effects, the presence of silver carp in the ponds decreased algal biomass through grazing and promoted nitrification providing and resuspending particles in the water column. These effects were also produced by mola, but were evident only in the absence of silver carp. Punti stirring on the pond bottom increased nutrient flow from the sediments into the water column and promoted nitrification, but were also evident only in the absence of silver carp.The addition of 10 silver carp over the 99 large carps stocked in the 100 m² fishponds did not affect punti and mola reproduction in the ponds, negatively affected rohu and catla growth and yield by about 20-25% but not their survival, did not affect common carp performance, reduced punti harvested biomass by 10%, reduced mola performance by about 50%, and silver carp's own biomass increased total yield and total income in about 20% each. The addition of 250 mola or punti to the large carp polycultures did not affect the performance of any of the large carps. The decreased income from selling the more expensive large carps was more than compensated by that obtained from silver carp, which increased total income by 13-24% as compared to the corresponding treatments without silver carp. This allows the option to the farmer of selling part of the silver carp to complete the cash income that would have been obtained from large carps only if silver carp would not be stocked, and consume the rest with the family.     

Factors affecting outbreaks of epizootic ulcerative syndrome in farmed fish in Bangladesh*

Abstract. Among 257 Bangladesh fish ponds investigated, 46% were affected by epizootic ulcerative syndrome (EUS) either fully or partially. Thai silver barb, Puntius gonionotus (Bleeker), culture ponds were worst affected (64%) by EUS, while all Nile tilapia, Oreochromis niloticus (L.), monoculture ponds remained unaffected. Stocking of silver barb for culture, use of piscicides as means of moving predators or unwanted species prior to stocking of cultured species, and culture of fish in previously derelict ponds are factors which significantly affected the probability of occurrence of EUS. Choice of species other than silver barb and use of lime during the post-stocking period significantly affected the probability of pond stocks being less adversely affected by EUS.     

Detection of Vibrio cholerae and Vibrio vulnificus by duplex PCR specific to the groEL gene

Vibrio cholerae and V. vulnificus are of major concern due to their effect on public health throughout the world. It is therefore imperative to identify a gene and method that are suitable for the accurate species-specific detection of these two species. A duplex polymerase chain reaction (PCR) assay was developed using two sets of primers targeting the groEL gene for the accurate simultaneous detection of V. cholerae and V. vulnificus. The nucleotide sequence of the groEL gene was compared with the sequences of other Vibrio and non-Vibrio species. The specificity of two primer sets for duplex PCR was checked using 24 Vibrio and 8 non-Vibrio species. The primer sets were found to be specific for these two species and could detect both of the target bacterial species without any ambiguity, even when comparing closely related species. For both species, the detection limit was 100 pg of purified genomic DNA. The duplex PCR showed high specificity and sensitivity for each species and was sufficient for the detection of V. cholerae and V. vulnificus from artificially infected shellfish tissue, flounder, and even inoculated seawater. This method is simple and cost-effective, and can be utilized for the simultaneous detection of both species, thus representing an effective tool for both epidemiologist and ecologist.     

High gene flow in two migratory Neotropical fish species,Salminus franciscanus and Brycon orthotaenia,and implications for conservation aquaculture

1. Two migratory and endangered freshwater fish species, Salminus franciscanus and Brycon orthotaenia, are endemic to one of the most important basins for hydropower capacity in South America. These two fish are target species of conservation aquaculture programmes along the São Francisco River system.
2. In order to implement effective strategies for the conservation of these species, microsatellite markers were developed and used to assess the genetic diversity and structure among wild groups. Fish were collected during the spawning season at four sampling sites, covering more than 1000 km.
3. Polymorphism loci were assessed, and a total of 133 and 107 alleles were found for S. franciscanus and B. orthotaenia, respectively. Despite the critical conservation status, B. orthotaenia showed high levels of genetic diversity, comparable with those of other closely related species.
4. Salminus franciscanus exhibited half of the genetic diversity of its sister species in terms of allelic diversity, indicating that this species will be more prone to genetic drift and inbreeding in conservation aquaculture programmes.
5. The results of an analysis of molecular variance for microsatellite markers in these species (F_ST = 0.007 for S. franciscanus and F_ST = 0.003 for B. orthotaenia) and the estimated recent migration rates (>40% among sampling sites) support panmixia in both species, despite the heterogeneities of the riverscape.
6. The results of this study and the microsatellites developed will play an important role in assisting agencies in making informed decisions on conservation aquaculture programmes.

     

Compatibility of silver barb Puntius gonionotus (Bleeker) with Indian major carps in a grow-out polyculture

The compatibility and growth performance of silver barb Puntius gonionotus (Barbonymous gonionotus) with the three Indian major carps, i.e., Catla catla, Labeo rohita and Cirrhinus mrigala, were assessed in a 10‐month carp polyculture trial. Treatments T‐1, T‐2, T‐3 and T‐4 were stocked with three of the above four carp species, with an absence of silver barb, mrigal, rohu and catla, respectively, while all four species were stocked in treatment T‐5. The treatments were stocked at 6000 fingerlings ha⁻¹, with an equal species ratio maintained in each treatment. Incorporation of silver barb into the polyculture system neither affected the survival of any carp irrespective of species combination nor yielded significant changes in biomass production among treatments, except for the one without catla, where it was significantly low. The study revealed a higher extent of competition between silver barb and rohu, perceptible from the lower growth of one in the presence of the other. Although a certain level of competition of silver barb with mrigal was evident, competition with catla was not perceptible. Irrespective of species combination with silver barb as a component species, similar total biomass production in treatments revealed the feasibility of its incorporation into the Indian major carp‐based polyculture practice without affecting the total yield.     

Development and characterization of a fibroblastic‐like cell line from caudal fin of the red‐line torpedo,Puntius denisonii (Day) (Teleostei: Cyprinidae)

A fibroblastic‐like cell line was established from the ornamental fish, red‐line torpedo (Puntius denisonii). The red‐line torpedo fin (RTF) cell line is being maintained in Leibovitz's L‐15 medium supplemented with 10% fetal bovine serum (FBS) for over 1 year at 28 °C on a continuous basis in normal atmosphere. The growth rate of RTF cells increased as the FBS proportion increased from 5% to 20% at 28 °C with optimum growth at the concentrations of 10% FBS. The morphology of RTF cell was predominantly fibroblastic like. Propagation of these cell lines was serum dependent, with a low plating efficiency (<15%). Karyotyping analysis of RTF cells at the 25th passage indicated that the modal chromosome number was 2n=50. The cell line was cryopreserved in liquid nitrogen at ?196 °C and could be recovered from storage after 6 months with good cell viability. Polymerase chain reaction amplification of a fragment of two mitochondrial genes, 16S rRNA and CO1, confirmed the identity of these cell lines with those reported from this animal species, confirming that the cell lines originated from P. denisonii. The bacterial extracellular products from Vibrio cholerae MTCC3904 and Aeromonas hydrophila were found to be toxic to RTF. The cell lines were not susceptible to viral nervous necrosis virus, a marine fish virus.     

Genetic improvement for important farmed aquaculture species with a reference to carp,tilapia and prawns in Asia: achievements,lessons and challenges

This study provides an overview of successful genetic improvement programmes for important farmed aquaculture species in Asia, with a focus on lessons and experiences gained as well as challenges remaining. In both fish and prawns (Macrobrachium rosenbergii), conventional selective breeding approaches have resulted in significant improvement in productivity, with genetic gains ranging from 8 to 12% per generation. Selection for high growth has also brought about beneficial changes in fillet weight of fish and edible meat in prawns without detrimental effects on flesh quality attributes and fitness‐related traits. Genetically improved animals show remarkable vigour and high adaptation to a range of culture environments/conditions in Asian countries. Despite these successes, however, the conduct and practical implementation of such breeding programmes still present several challenges. These include the expansion of breeding objectives, management of inbreeding in closed‐selection populations, controlling the effects of genotype by environment interactions, simultaneous production of large number of full‐ and half‐sib families for species with asynchronous spawning behaviour, maintaining pedigree records, dissemination of the improved strains for widespread production, as well as a reluctance by many to carry out systematically designed genetic improvement for aquatic animal species. There are also challenges with regard to the application of genomic information in genetic enhancement programmes and the development of genetically improved strains in response to climate and environmental changes. In this study, each of these challenges is discussed and solutions are proposed to increase efficiency of future genetic improvement programmes for economically important aquaculture species.     

Genetic diversity and population structure of burbot Lota lota in Germany: Implications for conservation and management

The genetic structure of the gadiform fish species, burbot Lota lota L., was investigated across Germany to derive management options for facilitating the preservation of genetic diversity. Sequence analysis of the mitochondrial control region (n = 244) and microsatellite analysis (n = 861) of specimens from 20 sites revealed genetic structuring between major river basins, and particularly between lake and river habitats. The admixture zone between the Eurasian and West European phylogenetic clades in Lake Constance was confirmed and expanded to include the drainage basins of the rivers Rhine and Schlei/Trave. Haplotype distribution and private haplotypes in single river basins indicated population differentiation and imply that German burbot constituted an important part of the entire species' diversity. The derived genetic structuring has implications for future stocking programmes and the preservation of the adaptive potential of burbot, a guiding species for oligotrophic lakes in Europe.     

Impact of Aeration on the Growth Performance of Silver Barb,Puntius gonionotus,during Fingerling Rearing

Impact of aeration on growth of silver barb, Puntius gonionotus during fingerling rearing was studied through a 100‐d rearing experiment conducted in 18 concrete tanks of 50 m² (10 × 5 × 1.2 m) size. Fry (0.74 ± 0.27 g, 35 ± 6 mm) were stocked in the experimental tanks at three stocking densities (25, 50, and 75 fry/m²) and were evaluated with and without provision of 6 h (2400–0600 h) of night time aeration. Aeration resulted in higher pH and dissolved oxygen regime and increased fingerling length and weight. The results suggest a rearing density of 75/m² to be ideal for rearing fry to fingerling of this species when aeration is provided, whereas, under non‐aerated condition, rearing the fry to fingerling stage at 50/m² was found advantageous over those at 25 and 75/m².     

Disease problems of prawns in recirculation systems in the U.K.

Prawn diseases encountered by the authors during research programmes on prawn cultivation are described and discussed. A variety of seawater penaeid species, the freshwater caridean Macrobrachium rosenbergii, and the seawater caridean Palaemon serratus were affected. Poor husbandry, in terms of holding tank design, water quality and/or inadequate nutrition, is often the major factor precipitating prawn disease. Attention to husbandry techniques and the routine monitoring of water quality are of paramount importance in the prevention of disease outbreaks. The significance of disease to prawn cultivation, either as a direct cause of mortalities or as a limitation to market sale, is highlighted.     

Reproductive Biology of Puntius sarana, an indigenous species, and Tilapia rendalli (melanopleura), an exotic, in an Ancient Man-Made Lake in Sri Lanka

Investigations on the reproductive biology of Puntius sarana an indigenous species and Tiiapia remialli (melanopleura) an exotic, in an ancient man-made lake, Parakrama Sarnudra (Sea of Parakrama), in Sri Lanka, carried out from February 1978 to May 1979 are presented. The overall female to male ratio in T. rendalli and P. sarana were 1.1:1.0 and 1.5:1.0, respectively. Considerable deviation from the mean ratio was observed and are attributed to their spawning behaviour and migrations. In the larger size groups in T. rendalti males were dominant while the reverse was observed in P. sarana. Both species were found to breed through out the year, with well defined peaks in the case of P. sarana which were coincidental with the main rainy seasons. Both species are multiple spawners, fecundity ranging from 760 to 6160 in T. rendalli with length and weight varying from 18.8 to 25.8 cm and 126 to 380 g, respectively. In P. sarana. with a length of 23.8–38.0cm and a weight of 180–792 g, fecundity ranged between 16,000 and 290,000.     

Habitat suitability index models for the juvenile soles,Solea solea and Solea senegalensis,in the Tagus estuary: Defining variables for species management

Habitat suitability index (HSI) models were used to map habitat quality for the sympatric soles Solea solea and Solea senegalensis in the Tagus estuary, Portugal. The selection of input variables to be used in these models is crucial since the recollection of such data involves important human and time resources. Various combinations of variables were developed and compared. Habitat maps were constructed for the months of peak abundance of S. solea and S. senegalensis consisting of grid maps for depth, temperature, salinity, substrate type, presence of intertidal mudflats, density of amphipods, density of polychaetes and density of bivalves. The HSI models were run in a Geographic Information System by reclassifying the habitat maps to a 0–1 suitability index scale. Following reclassification, the geometric mean of the suitability index values for each variable was calculated by grid cell, using different combinations of variables, and the results were mapped. Models performance was evaluated by comparing model outputs to data on species’ densities in the field surveys at the time. Further model testing was performed using independent data. Results show that there are two areas that provide the highest habitat quality. The model that combined density of amphipods and the abiotic variables had the highest correlation with the distribution of S. solea while the combination of density of polychaetes and the abiotic variables had the highest correlation with S. senegalensis distribution. These variables should be taken into account in future management plans, since they indicate the main nursery grounds for these species.     

Comparaison de la croissance et de la composition chimique d'Oreochromis (Tilapia) niloticus L. et de Cichlasoma (Theraps) melanurum Gth. Nourris avec Azolla

The growth of two species of Cichlidae, the African Oreochromis niloticus and the Central American Cichlasoma melanurum, fed with three different diets (100% pellets, 50% pellets and 50% Azolla, 100% Azolla) was compared. The growth performances of O. niloticus (G=2.3) fed only with pellets were higher than those of C. melanurum (G=0.9). With the mixed diet (50% pellets and 50% Azolla) growth was reduced for both species but this reduction was proportionally lower with C. melanurum. The fish fed exclusively with Azolla showed negative growth but fish weight loss was least for C. melanurum.Comparison of the chemical composition of the two fish species reveals significant differences. Generally moisture is lower for C. melanurum and lipid concentration is higher for this species with all three diets. Fed with Azolla, both species have a higher moisture and lower lipid concentration. Crude protein concentration (±15%) is very similar for both species regardless of diet.In conclusion, for intensive fish culture based on commercial pellets, the African species O. niloticus performs better than the American C. melanurum. On the other hand, the use of Azolla as feed for these fish does not seem very satisfactory but experiments should be conducted with typical herbivorous Cichlidae which may be able to utilize this fern in agro-piscicultural ecosystems.     

Molecular cytogenetic study in Octopus (Amphioctopus) areolatus from Japan

Octopus (Amphioctopus) areolatus is an important marine cephalopod in Japan. We examined its diploid chromosome number, karyotype, and genome size (C value), and performed fluorescence in situ hybridization (FISH) using a vertebrate telomeric probe. The diploid chromosome number was 60 in embryonic cells, with 24 pairs of metacentric chromosomes, four pairs of metacentric/submetacentric chromosomes, and two pairs of submetacentric chromosomes. The mean C value was estimated to be 5.47 pg. From these findings, and those reported previously for other octopus species, we suggest that the factor causing the quantum change of C value in O. (A.) areolatus was genome duplication, and not polyploidy. In telomeric FISH analysis, hybridization signals were clearly observed in the telomeric regions of the chromosomes. This is the first report of FISH analysis of cephalopod chromosomes, and our findings suggest that the telomere sequence of O. (A.) areolatus is (TTAGGG) _n , which may allow gene mapping in the future.     

Experimental effects of salinity on gonad growth and maintenance in small tropical freshwater ostariophysans

A selection of cyprinids of the genera Rasbora and Puntius, various neotropical characins and a species of kuhli loach, Pangio semicincta, were exposed to different salinity regimes (in the conductivity range 0--2000 S cm–1), to determine whether there was any effect on gonadal development. There was no conclusive evidence for such an effect in any species, although there was a trend for ovarian development to be somewhat reduced at high conductivities in some species. These results appear to refute any suggestion that, in the wild, changes in environmental salinity may play any considerable role in the regulation of gonadal cycles of small non-electroreceptive tropical freshwater teleosts     

Use of Rotenone as Piscicide: Toxicity Levels in a Few Common Freshwater Predatory and Weed Fishes

Toxicity of rotenone was studied in a few common freshwater predatory and weed fishes through wet laboratory experiments for its use as a piscicide during pond preparation. Cube root powder (CRP) (ENT-133 Rotenone) containing 9% rotenone was used as the toxicant source. Lethal concentration of CRP for these common predatory and weed fishes varied between 0.75–2.70 mg L^?1 (0.068–0.243 mg L^?1 of rotenone). Acute toxicity study revealed Puntius sophore to have more susceptibility to rotenone toxicity with 24 h LC₅₀ value of CRP at 0.50 mg L^?1 (0.045 mg L^?1 rotenone) compared to 1.17 mg L^?1 (0.105 mg L^?1 rotenone) in Anabas testudineus and 1.90 mg L^?1 in Channa punctatus (0.171 mg L^?1 rotenone); while Heteropneustes fossilis showed higher tolerance with 24 h LC₅₀ value at 2.42 mg L^?1 (0.218 mg L^?1 rotenone). Such result suggested rotenone toxicity to depend on the respiratory behavior of fish. The marginal reduction in 48 h LC₅₀ of CRP compared to its 24 h value and no fish mortality beyond 48-h in all tested species suggested faster degradation of the toxicant in water. Since application of the piscicide aims at eradication of all commonly available species of predatory and weed fishes in the culture pond, the study suggested a dose of 2.5 mg L^?1 of CRP (0.225 mg L^?1 rotenone) for pond application.     

Determination of allogeneic and xenogeneic markers in the genus of Tilapia. II. Identification of T. aurea,T. vulcani and T. nilotica by electrophoretic analysis of their serum proteins

Sera from Israeli stocks of T. nilotica, T. vulcani and T. aurea were analysed, by polyacrylamide gel electrophoresis, for the existence of species-specific markers. Markers situated in the fast region of the electropherogram were found to be male sex and species specific. Interspecies polymorphism in markers in the post albumin area (transferrins) permit the distinction between these related species of Tilapia. No significant polymorphism was found in the electropherogram of T. vulcani. T. aurea presented some slight variations in the transferrin zone, and T. nilotica displayed a high polymorphism everywhere along the electropherogram. Two other species specific bands were found in the prealbumin zone; bands 1 (specific for T. aurea) and 2 (specific for T. vulcani). A selection of fish stocks of T. aurea and T. vulcani is currently done now on the basis of this electrophoretic criteria and on the ability to produce a high percentage of male hybrids. It was concluded that the stock of T. nilotica which exist in Israel do not represent the pure species of T. nilotica. The failure to obtain 100% males in all paired interspecific mating (Pruginin et al., 1975) was explained on this basis.