Aquaculture Center Research Articles

Emergence of Edwardsiella piscicida in Farmed Channel ♀, Ictalurus punctatus × Blue ♂, Ictalurus furcatus, Hybrid Catfish Cultured in Mississippi

AbstractThere is a trend toward the increased incidence and prevalence of Edwardsiella piscicida septicemia in US catfish aquaculture, particularly in channel ♀, Ictalurus punctatus, × blue ♂, I. furcatus, hybrid catfish. From 2013 to 2017, a total of 3242 disease case submissions were made to the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, MS. Of these, 1400 (43.2%) were hybrids. E. piscicida was suspected in 138 (4.3%) of cases, the majority of which (89.1%) were from hybrid catfish. A molecular survey of these isolates confirmed the majority (92.0%) to be E. piscicida. Furthermore, cases of E. piscicida from hybrids submitted to the ARDL and the Aquatic Diagnostic Laboratory of the Mississippi State University College of Veterinary Medicine in Starkville, MS, were documented for gross lesions and histological analysis. Grossly, E. piscicida presents with small dermal ulcerations, a raised fluid‐filled cranial midline lesion that is frequently ulcerated, hemorrhage in the gills, exophthalmia, and abdominal distension. Internally, lesions include splenomegaly, straw‐colored ascites, renomegaly, and occasionally hemorrhagic intestines. Histopathological examination is in agreement with gross observations, and infected fish repeatedly demonstrate a mononuclear meningoencephalitis, hemorrhagic branchitis, splenitis, ulcerative dermatitis, granulomatous interstitial nephritis, and hepatitis coupled with a hemorrhagic enteritis.

Correlation between Oxygen Demand of Nematode Communities with Dissolved Oxygen in the Organic Shrimp Farming Ponds, Ca Mau Province

Correlation between Oxygen Demand of Nematode Communities with Dissolved Oxygen in the Organic Shrimp Farming Ponds, Ca Mau Province

Macroalgas exoticas en la costa de Chile: patrones espaciales y temporales en el proceso de invasion

In this paper we propose a checklist of 14 species of exotic seaweeds on the Chilean coast, and three species which, being native to the Chilean coast, have been introduced in areas outside their natural range. This list was compiled from previously published checklist, debugged the misidentified records, and incorporating new ones. The distribution of exotic seaweeds is not homogeneous along the coast, but it is concentrated in areas near ports and aquaculture centers. Most species display a fairly bounded distribution, and only four tend to invade ( i.e ., increase its range of distribution over time). However, considering that most introductions are recent (the last 60 years) and the positive relationship between amplitude of the distribution range and residence time of species on the Chilean coast, we suggest that some of these species may be in an expansion phase, which would explain its restricted distribution. This work not only updates the information related to exotic seaweed on the Chilean coast, but also allows us to understand the invasion process, through the analysis of the patterns described in these systems.

Genetic diversity and population structure of the African catfish, Clarias gariepinus (Burchell, 1822) in Kenya: implication for conservation and aquaculture

African catfish, Clarias gariepinus, is an important species in aquaculture and fisheries in Kenya. Mitochondrial D-loop control region was used to determine genetic variation and population structure in samples of C. gariepinus from 10 sites including five natural populations (Lakes Victoria (LVG), Kanyaboli (LKG), Turkana (LTA), Baringo (LBA) and Jipe (LJP), and five farms (Sangoro Aquaculture Center (SAN), Sagana Aquaculture Centre (SAG), University of Eldoret Fish Farm (UoE), Kibos Fish Farm (KIB), and Wakhungu Fish Farm (WKU)) in Kenya. Similarly, samples from eight localities (four natural populations: LVG/LKG, LTA, LBA, and four farmed: SAN, SAG, KIB, UoE) were genotyped using six microsatellite DNA loci. For the D-loop control region, samples from natural sites exhibited higher numbers of haplotypes and haplotype diversities compared to farmed samples, and 88.2% of haplotypes were private. All except LJP and LTA shared haplotypes, and the highest number of shared haplotypes (8) was detected in KIB. The 68 haplotypes we found in 268 individuals grouped into five phylogenetic clades: LVG/LKG, LTA, LBA, LJP and SAG. Haplotypes of farmed C. gariepinus mostly have haplotypes typical of LVG/LKG, and some shared haplotypes of the LBA population. Microsatellite analysis showed farmed samples have higher numbers of alleles than natural samples, but higher observed and expected heterozygosity levels were found in samples of natural populations. Fifteen pair-wise comparisons had significantly different FST values. All samples were in Hardy-Weinberg equilibrium. Samples from the eight localities grouped into four genetic clusters (LVG/LKG, LTA, LBA and SAG), indicating genetically distinct populations, which should be considered for aquaculture and conservation.

PLANKTON COMMUNITY STRUCTURE ON FISH PONDS IN THE RIAM KANAN RIVER OF BANJAR REGENCY

Aquaculture in Riam Kanan river receives watersupply from rivers and Riam Kanan reservoir from upstream to downstream and practices different irrigation and fertilization systems. This study was aimed to compare the plankton community structure, to find out the physicalchemical parameters associated with the abundance of plankton and the fertility of the fish-farming ponds. The research was conducted at Mandiangin Freshwater Aquaculture Center (Balai Budidaya Air Tawar – BBAT), Karang Intan (Balai Benih dan Induk Ikan Air Tawar – BB-IAT) and Cindai Alus Minapolitan area by using the observation method. Water samples were taken by composite of 6 replicates at 12 stations. The parameters measured were temperature, visibility, pH, iron, free ammonia, nitrate, phosphate, DO, BOD and plankton analysis. Data were tested statistically with cluster, Pearson correlation and regression. The result shows that there are differences in plankton community structure in the fish ponds, shown by 5 cluster groups. The abundance of phytoplankton has a significant correlation with pH, temperature, DO, and free ammonia. The abundance of zooplankton also has a significant correlation with pH, DO, BOD, and free ammonia. The seed pond at BBAT Mandiangin is eutrophically dominated by Bacillarophyta and Amoboezoa, while in BB-IAT Karang Intan and Cindai Alus are dominated by Cyanophyta and Rotifera. The inlet channel of BB-IAT Karang Intan and the broodstock pond belong to mesotrophic category, predominance by Cyanophyta, Chlorophyta and Rotifer. BBIAT Karang Intan outlet ponds, BBAT Mandiangin inlet channel and Cindai Alus inlet pond are included in the oligotrophic category, predominance by Cyanophyta and Chlorophyta. Plankton community structure of the fishfarming pond varies even with the same ecological conditions.

Colorful invasion in permissive Neotropical ecosystems: establishment of ornamental non-native poeciliids of the genera Poecilia/Xiphophorus (Cyprinodontiformes: Poeciliidae) and management alternatives

ABSTRACT Headwater creeks are environments susceptible to invasion by non-native fishes. We evaluated the reproduction of 22 populations of the non-native livebearers guppy Poecilia reticulata, black molly Poecilia sphenops, Yucatan molly Poecilia velifera, green swordtail Xiphophorus hellerii, southern platyfish Xiphophorus maculatus, and variable platyfish Xiphophorus variatus during an annual cycle in five headwater creeks located in the largest South American ornamental aquaculture center, Paraíba do Sul River basin, southeastern Brazil. With few exceptions, females of most species were found reproducing (stages 2, 3, 4) all year round in the creeks and gravid females of all species showed small sizes indicating stunting. Juveniles were frequent in all sites. The fecundity of the six poeciliids was always low in all periods. The sex ratio was biased for females in most species, both bimonthly as for the whole period. Water temperature, water level and rainfall were not significantly correlated with reproduction in any species. Therefore, most populations appeared well established. The pertinence of different management actions, such as devices to prevent fish escape, eradication with rotenone and research about negative effects on native species, is discussed in the light of current aquaculture practices in the region.

Seasonal distribution of dissolved iron in the surface water of Sanggou Bay, a typical aquaculture area in China

Sanggou Bay (SGB) is one of the largest aquaculture centers in China. Although iron is an essential biological element, little is known about its distribution in this bay. In this study, seasonal distributions of dissolved iron (dFe) in the surface water of SGB and its surrounding rivers and groundwater were investigated during the four seasons from April 2013 to January 2014. Our results indicate that SGB is a source of dFe on the bay scale. The average dFe concentrations in the surface water of SGB were 12.0±6.29nM in spring, 5.00±2.92nM in summer, 1.83±0.42nM in autumn, and 3.36±2.06nM in winter. External sources of dFe in SGB were ranked in the following order: atmospheric deposition>sediment diffusion>groundwater input>riverine input. The biological iron of the cultivated species (kelp, scallops, and oysters) was the main sink for dFe in SGB. The calculation of Fe⁎P (a tracer defined to quantify the degree of iron limitation in water relative to phosphorus) suggested that dFe was sufficient to support the biological utilization of dissolved inorganic phosphorus in spring and summer but was a potentially limiting factor for primary production in autumn.

Assessment of apparent effectiveness of chemical egg disinfectants for improved artificial hatching in Oreochromis karongae (Pisces: Cichlidae)

Oreochromis karongae is one of the three key Tilapia species locally known as ‘Chambo’ which is endemic to Lake Malawi. The species is favored by consumers and due to high demand its catches have significantly declined over time. Aquaculture holds the potential to supplement catches as well as produce seed for restocking purposes. However, seed production of O.karongae in artificial hatcheries has registered little success due to high egg and fry mortalities. Therefore, a study was conducted to compare the apparent effectiveness of three chemical egg disinfectants in an attempt to improve hatching success and reduce fry mortality in O. karongae in an artificial re-circulating incubation system at the National Aquaculture Center, Domasi, Malawi. Batches of 200 stage II eggs were immersed for 5 minutes in 50ml solutions of (1) 50mg/l Potassium Permanganate, (2) 500mg/l Formalin, (3) 1000mg/l Sodium Chloride, (4) 5000mg/l Sodium Chloride, while treatment (5) was a control without any chemical treatment. Each treatment was replicated three times in 1.2 L plastic incubation jars with continuous water flow rate of 0.17 l/s operated at 10% daily water replacement. There was significantly low total mortality and high hatchability in treatments (1), (2) and (3) than (4) and (5) (p<0.05). The results provided evidence that pre-incubation egg treatment using chemicals has potential to significantly reduce mortalities and increase fry production in an artificial re-circulating incubation system. It is recommended, based on the findings that lower concentrations of sodium chloride, being a safer and less toxic chemical can be used for disinfecting O.karongae eggs. Future studies should focus on undertaking a toxicity test with various levels of the chemical disinfectants to identify optimum doses. This should be coupled with microbiological assays to validate the apparent effectiveness found in this study and identify the key microbial species that are responsible for mortalities during incubation of O.karongae eggs in a re-circulating system. Key words: Egg, disinfectants, incubation, recirculation, hatchability, egg treatment, mortality, Oreochromis karongae

Myxobolus ictiobus n. sp. and Myxobolus minutus n. sp. (Cnidaria: Myxobolidae) from the gills of the smallmouth buffalo Ictiobus bubalus Rafinesque (Cypriniformes: Catostomidae).

The smallmouth buffalo Ictiobus bubalus Rafinesque (Catostomidae) is native to North American waterways and occasionally grown in pond aquaculture. Species of Myxobolus Bütschli, 1882 have been reported from the gills, integument, and intestinal tract of buffalo fish, although there is ambiguity in some host records. In the summer of 2013, thirteen adult smallmouth buffalo were seined from a 0.1-acre (0.04-hectare) experimental research pond at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, Mississippi, USA, and examined for the presence of parasitic infection. Two previously unknown species of Myxobolus were observed parasitising the gills. Plasmodia of the two species differed from each other in both size and shape. Morphologically the two species were distinct from one another and from other Myxobolus spp. previously reported from buffalo fish. Myxospores of Myxobolus ictiobus n. sp. were spherical and measured 12.7-14.5 (13.9 ± 0.4) µm in length and 10.7-13.6 (12.5 ± 0.7) µm in width with a thickness of 10.3-14.8 (12.6 ± 2.3) µm. Polar capsules measured 5.6-7.4 (6.6 ± 0.4) µm in length and 3.7-4.9 (4.5 ± 0.8) µm in width and each contained a coiled polar filament with 5-6 turns. Myxospores of Myxobolus minutus n. sp. were circular in shape and measured 7.4-9.6 (8.6 ± 0.7) µm in length and 7.5-9.9 (8.8 ± 0.7) µm in width with a thickness of 6.5-7.3 (6.7 ± 0.3) µm. Polar capsules measured 3.6-4.9 (4.3 ± 0.3) µm in length and 2.8-3.8 (3.3 ± 0.3) µm and each contained a coiled polar filament with 5-6 turns. Supplemental 18S rRNA gene sequencing identified unique sequences for each isolate. Phylogenetic analysis of 18S rRNA sequences demonstrated a strong clustering of both isolates with other species of Myxobolus from cypriniform fish.

Costs and Risk of Catfish Split‐pond Systems

AbstractSplit ponds are recently developed pond‐based aquaculture systems that allow intensification of catfish aquaculture. Successful industry‐wide adoption of newly developing technologies like split‐pond systems will depend upon their productivity and cost efficiencies. Costs and production performance of the following three split‐pond design scenarios were monitored in Arkansas and Mississippi: (1) research design developed at the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi; (2) waterwheel design tested on commercial catfish ponds; and (3) screw‐pump design tested on commercial catfish ponds. An economic engineering approach using standard enterprise budget analysis was used to develop estimates of breakeven prices (BEPs) ($/kg) for producing foodsize hybrid catfish (♂Ictalurus furcatus × ♀Ictalurus punctatus) for each scenario. Estimates of BEPs of hybrid catfish raised in split ponds ranged from $1.72 to $2.05/kg. The cost of catfish production in split ponds was sensitive to yield, fish prices, and feed prices. Annual net cash flows from both commercial split‐pond systems were high and sufficient to make the investment profitable in the long run. Feed price, feed conversion ratio, and yield contributed the most to downside risk of split ponds.

Isolation, Characterization and Virulence Potential of Tenacibaculum dicentrarchi in Salmonid Cultures in Chile.

In this study, we isolated, identified and characterized isolates of Tenacibaculum dicentrarchi in Atlantic salmon (Salmo salar) farmed in Chile for the first time. In 2010 and 2014, mortalities were observed in Atlantic salmon (average weight 25-30 and 480-520g, respectively) at an aquaculture centre in Puerto Montt, Chile. Severe tail rots, frayed fins and, in some cases, damaged gills were detected. Wet smear analyses of these lesions revealed a high occurrence of Gram-negative, filamentous bacteria. Microbiological analysis of infected gill and tail tissues yielded six bacterial isolates. All were identified as T.dicentrarchi through polyphasic taxonomy, which included phenotypic characterization, 16S rRNA sequencing and multilocus sequence typing. The latter method revealed a close relationship of the Chilean genotype with the T.dicentrarchi type strain and two Norwegian Atlantic cod (Gadus morhua) isolates. The pathogenic potential of the TdChD05 isolate was assessed by challenging Atlantic salmon and rainbow trout (Oncorhynchus mykiss) for one hour, which resulted in mean cumulative mortality rates of 65% and 93%, respectively, as well as clinical signs 14days post-challenge. However, challenged Coho salmon (Oncorhynchus kisutch) presented no mortalities or clinical signs of infection. These findings indicate that the geographical and host distribution of T.dicentrarchi is wider than previously established and that this bacterium may have negative impacts on salmonid cultures.

Comparison of Spawning Rate between Wild and Improved Strain of &lt;i&gt;Oreochromis shiranus&lt;/i&gt; (Boulenger, 1897)

The study was conducted to determine the spawning rate of Malawian Tilapia, Oreochromis shiranus bred in hapas and placed in ponds at the Malawi’s National Aquaculture Centre (NAC). Two strains compared were improved strain from fifth (F5) generation brooders which were procured from a selective breeding program and the wild strain. The brood stock fish were grouped into 3 size categories (24-59g which was designated as treatment 1), 60-99g brooders were denoted as treatment 2 and treatment 3 comprised of brooders that were >100g. Two reproductive parameters were measured every fortnight: number of eggs produced and condition factor (CF) of the fish. The results showed no significant differences in the number of eggs produced between improved and wild strain (P<0.05). The study has demonstrated the significance of using body weight and standard length in selecting both wild and improved strain as a selection criterion for brooders in Malawian Tilapia aquaculture industry.

Combining environmental suitability and population abundances to evaluate the invasive potential of the tunicate Ciona intestinalis along the temperate South American coast.

The tunicate Ciona intestinalis is an opportunistic invader with high potential for causing economic losses in aquaculture centers. Recent phylogenetic and population genetic analysis support the existence of a genetic complex described as C. intestinalis with two main dominant species (sp A and B) occurring worldwide. In Chile, the species has been observed around 30°S of latitude, but no official reports exist for the presence of C. intestinalis in southern regions (above 40°S), where most of the mollusk aquaculture centers are located. Here, we used occurrences from multiple invaded regions and extensive field sampling to model and validate the environmental conditions that allow the species to persist and to find the geographic areas with the most suitable environmental conditions for the spread of C. intestinalis in the Chilean coast. By studying the potential expansion of C. intestinalis southward in the Chilean Coast, we aimed to provide valuable information that might help the development of control plans before the species becomes a significant problem, especially above 40°S. Our results highlight that, by using portions of the habitat that are apparently distinguishable, the species seem to be not only genetically distinct, but ecologically distinct as well. The two regional models fitted for sp A and for sp B showed disagreement on which sections of Chilean coastline are considered more suitable for these species. While the model for sp A identifies moderately to highly suitable areas between 30° and 40°S, the model for sp B classifies the areas around 45°S as the most appropriate. Data from field sampling show a positive linear relationship between density of C. intestinalis and the index of suitability for sp A in aquaculture centers. Understanding the relation of the distinct species with the surrounding environment provided valuable insights about probable routes of dispersion in Chile, especially into those areas considered suitable for aquaculture activities but where the species has not yet been recorded. We discuss the implications of our findings as a useful tool to anticipate the invasion of such harmful invasive species with regard to the most relevant environmental variables.

Urban Land Use, Water Quality, and Biological Conditions in the Lower Mississippi River Basin Bayous

Urban Land Use, Water Quality, and Biological Conditions in the Lower Mississippi River Basin Bayous Yushun Chen, Kathryn Herzog, Sagar Shrestha, Daniel Grigas, John Farrelly, Christopher Laskodi & Matthew Skoog a Institute of Hydrobiology, Chinese Academy of Sciences, 7 South Donghu Road, Wuhan, Hubei 430072, China. E-mail: b Aquaculture and Fisheries Center, University of Arkansas-Pine Bluff, Pine Bluff, AR 71601 Published online: 01 Jul 2015.

Spatio-temporal evaluation of Yamchi Dam basin water quality using Canadian water quality index.

In recent years, the growth of population and increase of the industries around the tributaries of Yamchi Dam basin have led to deterioration of dam water quality. This study aimed to evaluate the quality of the Yamchi Dam basin water, which is used for drinking and irrigation consumptions using Canadian Water Quality Index (CWQI) model, and to determine the main water pollution sources of this basin. Initially, nine sampling stations were selected in the sensitive locations of the mentioned basin's tributaries, and 12 physico-chemical parameters and 2 biological parameters were measured. The CWQI for drinking consumptions was under 40 at all the stations indicating a poor water quality for drinking consumptions. On the other hand, the CWQI was 62-100 for irrigation at different stations; thus, the water had an excellent to fair quality for irrigation consumptions. Almost in all the stations, the quality of irrigation and drinking water in cold season was better. Besides, for drinking use, total coliform and fecal coliform had the highest frequency of failure, and total coliform had the maximum deviation from the specified objective. For irrigation use, total suspended solids had the highest frequency of failure and deviation from the objective in most of the stations. The pisciculture center, aquaculture center, and the Nir City wastewater discharge were determined as the main pollution sources of the Yamchi Dam basin. Therefore, to improve the water quality in this important surface water resource, urban and industrial wastewater treatment prior to disposal and more stringent environmental legislations are recommended.

Wet Season Variations of some Physicochemical Parameters of the Brackish Water farm, Buguma, Niger Delta, Nigeria

Some physicochemical parameters of Nigerian Institute for Oceanography and Marine Research/African Regional Aquaculture Centre (NIOMR/ARAC) brackish water fish farm; Buguma; Rivers State; Nigeria were monitored twice each month from April to October in 2011 and 2012; covering wet season for both years in the region. The result obtained indicates that for 2011 pH; ammonia-nitrogen; nitrite-nitrogen; nitrate-nitrogen; alkalinity; carbon (iv) oxide; salinity; dissolved oxygen and temperature ranges were between 6.5-7; 0-0.1 ppm; 0.25-0.25 ppm; 40-80 ppm; 5-10 ppm; 9-20 ppt; 3.8-6 ppm and 26-31oC respectively while for 2012 pH; ammonia-nitrogen; nitritenitrogen; nitrate-nitrogen; alkalinity; carbon (iv) oxide; salinity; dissolved oxygen and temperature ranges were between 6.5-7; 0-0.1 ppm; 0.05-0.05 ppm; 0.05-0.25 ppm; 40-80 ppm; 5-10 ppm; 9-20 ppm; 3.8-5.6 ppm; 26-31oC respectively. There were no significant differences (p>0.05) in all parameters for both years and the values measured were within tolerable limits for optimum aquaculture.

The Influence of Substrate to Larval Settlement of the Tropical Abalone (Haliotis asinina)

Larval settlement stage of abalone (Haliotis asinine) depends on availability of feed and substrate compatibility. Existing feed size and feed type diversity in substrate will affect larval settlement stage, feeding habit and survival rate of abalone larvae. This study aims to find out the most suitable substrate for larval settlement of the tropical abalone. It is conducted in February-April, 2013 at Brackish Water Aquaculture Center, Takalar Regency, South Sulawesi. Applied experimental design is Completely Randomized Design. There are 3 types of test substrate: coral, cement and plastic with 3 replications for each substrate. This study shows that statistically, substrate differences do not affect to larval settlement stage. The highest stage of larval settlement is to coral substrate by 3.3%, followed by cement and plastic by 2.2% and 0.2% respectively. The highest average stage of living larva on coral and cement substrate are 15.3%, while on plastic substrate is 8.7%.

Performance of Alternative Diets Containing Solvent‐Extracted Distillers Dried Grains with Solubles Compared to Traditional Diets for Pond‐Raised Channel Catfish, Ictalurus punctatus, and Hybrid Catfish, Ictalurus punctatus × Ictalurus furcatus

AbstractTwo concurrent pond studies were initiated in April 2011 to evaluate feeds containing solvent‐extracted distillers dried grains with solubles (SE‐DDGS) in both 28 and 32% protein catfish feeds. Channel catfish, Ictalurus punctatus, were stocked in multiple‐batch production ponds at the University of Arkansas at Pine Bluff (UAPB) and hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, in single‐batch production ponds at the National Warmwater Aquaculture Center (NWAC), Mississippi State University, Stoneville, Mississippi, USA. The experimental design was a 2 × 2 factorial with two protein levels (32 and 28% protein), with and without 20% SE‐DDGS. Fish were fed once daily to apparent satiation, and managed similarly to a commercial farm for 186 d at UAPB and 172 d at NWAC. For channel catfish, two‐way ANOVA showed significant effects of both protein level (28% being better than 32%) and protein source (20% SE‐DDGS diets being better than traditional diets) on yield, survival, total diet fed, and feed conversion ratio (FCR), due primarily to effects on the understocked fingerlings. Partial budget analysis suggested that the 28% protein diet with the 20% SE‐DDGS was preferred economically for the prevailing feed costs. For hybrid catfish, two‐way ANOVA did not show significant differences in total diet fed, yield, survival, and processing yields, but use of SE‐DDGS resulted in a lower FCR. Results showed that both channel and hybrid catfish can utilize 20% SE‐DDGS in the diet without adversely affecting production or processing characteristics.

Development of a bacterial challenge test for gnotobiotic Nile tilapia Oreochromis niloticus larvae

Gastrointestinal microbiota have an important impact on fish health and disease, stimulating interest in a better understanding of how these gastrointestinal microbial communities are composed and consequently affect host fitness. In this respect, probiotic microorganisms have been extensively used in recent aquaculture production. To study the use of probiotics in the treatment of infectious diseases, the establishment of a method of experimental infection to obtain consistent results for mortality and infection in challenge tests is important. In pathogen-screening tests, 4 candidate pathogenic bacteria strains (Edwardsiella ictaluri gly09, E. ictaluri gly10, E. tarda LMG2793 and Streptococcus agalactiae LMG15977) were individually tested on xenic Nile tilapia larvae. Only Edwardsiella strains delivered via Artemia nauplii, with or without additional pathogen delivery via the culture water, led to increased mortality in fish larvae. A gnotobiotic Nile tilapia larvae model system was developed to provide a research tool to investigate the effects and modes-of-action of probiotics under controlled conditions. A double disinfection procedure using hydrogen peroxide and sodium hypochlorite solution was applied to the fish eggs, which were subsequently incubated in a cocktail of antibiotic and antifungal agents. In the gnotobiotic challenge test, E. ictaluri gly09R was added to the model system via Artemia nauplii and culture water, resulting in a significant mortality of the gnotobiotic fish larvae. The developed gnotobiotic Nile tilapia model can be used as a tool to extend understanding of the mechanisms involved in host-microbe interactions and to evaluate new methods of disease control.

ANALISIS PENDAPATAN DAN RESIKO USAHA BUDIDAYA IKAN AIR TAWAR DI KABUPATEN BENGKULU SELATAN

The main objective of this study is to determine the income and financial risks of freshwater aquaculture, especially tilapia. The study was conducted in Seginim, South Bengkulu, with consideration that Seginim is an area of aquaculture centers in South Bengkulu. Samples have been taken as many as 50 tilapia farmers. Data analysis was using quantitative and qualitative models. Approach starts from the calculation of operating cost, revenue, and income, and then the study of risk analysis approached by variance analysis. The results show that the income of freshwater fish farming, tilapia in particular, is Rp 59,512,743.75 per period of production per farming unit, and the level of business risk is quite high with the number of CV more than 50% (&gt;0,5) and it has opportunity losing of income as much as minus Rp 7,127,386.37 per period of production. Keywords: Aquaculture, Freshwater Fish, Income, and Risk