Anguilla Australis Research Articles

Effect of Stocking Density on Growth, Biochemical Composition, and Blood Parameters in the Pacific Shortfin Eel (Anguilla bicolor pacifica) Elvers

This study examined the effect of stocking density on growth, biochemical composition, and blood parameters of the Pacific shortfin eel Anguilla bicolor pacifica. Elvers (1.95 ± 0.14 g body weight) were randomly stocked in indoor tanks and reared over 186 d at three stocking densities (0.3, 0.6, and 0.9 kg m-3) set up in triplicates. Except for survival and biometric indices, elvers maintained at 0.3 and 0.6 kg m-3 densities exhibited higher growth and feed utilization than those held at 0.9 kg m-3. Yield increased with stocking density, which were significantly higher at 0.6 and 0.9 kg m-3. RNA/DNA ratio did not reflect growth rate, but trends in survival and RNA/DNA ratio with stocking density were positively related. In contrast to body proximate composition, increasing stocking density resulted in significantly higher erucic acid (22:1n-9) and total saturated fatty acid levels at 0.6 and 0.9 kg m-3 densities, respectively. Serum glutamic pyruvic transaminase activity was significantly elevated at 0.6 kg m-3, while total protein, glucose, and triglycerides slightly decreased with increasing stocking density. Results suggest that Pacific shortfin eel elvers can be reared in indoor tanks at a stocking density of 0.3 – 0.6 kg m-3 to achieve acceptable growth, feed performance, and health condition.

Highly contiguous genome assembly and gene annotation of the short-finned eel (Anguilla bicolor pacifica)

In East Asia, anguillid eels are commercially important. However, unlike other species, they have not been successfully cultivated throughout their lifecycle. Facing population decline due to overharvesting and environmental pressures, the industry is turning to alternatives, such as Anguilla bicolor pacifica (short-finned eel). However, genomic data for short-finned eels are unavailable. Here, we present in-depth whole-genome sequencing results for short-finned eel obtained using two sequencing platforms (PacBio Revio, and Illumina). In this study, we achieved a highly contiguous genome assembly of the short-finned eel, comprising 19 pseudochromosomes encompassing 99.76% of the 1.087 Gb genome sequence with an N50 of 16.88 and 61.07 Mb from contig and scaffold, respectively. Transcripts from four different tissues led to the annotation of 23,095 protein-coding genes in the eel genome, 98.66% of which were functionally annotated. This high-quality genome assembly, along with the annotation data, provides a foundation for future functional genomic studies of short-finned eels.

Host and geography impact virus diversity in New Zealand’s longfin and shortfin eels

The fishing and aquaculture industry is vital for global food security, yet viral diseases can result in mass fish die-off events. Determining the viromes of traditionally understudied species, such as fish, enhances our understanding of the global virosphere and the factors that influence virome composition and disease emergence. Very little is known about the viruses present in New Zealand’s native fish species, including the shortfin eel (Anguilla australis) and the longfin eel (Anguilla dieffenbachii), both of which are fished culturally by Māori (the indigenous population of New Zealand) and commercially. Through a total RNA metatranscriptomic analysis of longfin and shortfin eels across three different geographic locations in the South Island of New Zealand, we aimed to determine whether viruses had jumped between the two eel species and whether eel virome composition was impacted by life stage, species, and geographic location. We identified nine viral species spanning eight different families, thereby enhancing our understanding of eel virus diversity in New Zealand and the host range of these viral families. Viruses of the family Flaviviridae (genus Hepacivirus) were widespread and found in both longfin and shortfin eels, indicative of cross-species transmission or virus-host co-divergence. Notably, both host specificity and geographic location appeared to influence eel virome composition, highlighting the complex interaction between viruses, hosts, and their ecosystems. This study broadens our understanding of viromes in aquatic hosts and highlights the importance of gaining baseline knowledge of fish viral abundance and diversity, particularly in aquatic species that are facing population declines.

Factors influencing migration of short-finned eels (Anguilla australis) over 3 years from a wetland system, Lake Condah, south-east Australia, downstream to the sea.

Anguillid eel populations are under threat globally. A particularly vulnerable life-cycle stage is the migration of mature adult eels downstream from freshwater habitats through estuaries into the sea to spawn. This study investigated the factors associated with downstream migration of the short-finned eel Anguilla australis (Richardson 1841) from a coastal wetland (Lake Condah) in south-east Australia, using acoustic telemetry. Migration was associated with time of the year, higher water level and river flows, decreasing water temperature, and darker moon phases. Larger individuals and those in better condition were more likely to migrate from the wetland. Downstream migration peaked in spring, in contrast to the typical autumn migration period for other temperate anguillids. Variable responses, in comparison to other studies, highlight how migration cues may not be universal. In south-east Australia, short-finned eels may have evolved to migrate in multiple phases by first migrating to the estuary during typical seasonal spring flow pulses (e.g., to avoid being stranded in upland reaches during dry summer periods) and then migrating into the ocean in autumn. More research is needed to unravel these processes and causes, especially considering that the relationship between migration and hydrology may be complex and confounded (e.g., by human-induced disruptions to migratory pathways).

Effects of point-source discharges on shortfin eels (Anguilla australis) along the Waikato River, New Zealand

ABSTRACT The Waikato River is the longest river in New Zealand and is exposed to range of anthropogenic stressors. This study investigated the effects of three major point-source discharges on resident shortfin eels Anguilla australis along the river. Shortfin eels were caught from sites upstream and downstream of discharges of bleached kraft mill effluent (BKME) from pulp and paper manufacture, sewage, and a thermal power plant. At each site, population parameters (relative abundance and age structure) and individual metrics of health such as condition factor and organ (gonad, liver, and spleen) to somatic weight ratios were measured. Blood, biochemical (hepatic 7-ethoxyresorufin-O-deethylase or EROD) and chemical markers (bile chemistry and trace elements in flesh) were also measured. Measures of exposure and response to discharges confirmed that the shortfin eels were resident at the sites sampled. The discharges had few negative impacts on individual eel health and positive responses were seen to warm water discharge. However, resident shortfin eels were immature so reproductive responses could not be determined. In conclusion, shortfin eels in this study showed few responses to the effects of the discharges except for increased resin acids, bile polycyclic aromatic hydrocarbons, and EROD at the BKME site.

Characterization and Effect of Processing on Parvalbumin Content in Indonesian Shortfin Eel (Anguilla Bicolor-bicolor)

Indonesian shortfin eel (Anguilla bicolor bicolor) is a high economic value fish and a high nutritional content. However, their utilization can be limited because of hypersensitivity cases in individuals allergic to fish. This study aimed to determine the characteristics of the fish major allergenic protein, parvalbumin in different parts of the eel fillet and the effects of boiling technique on the content of this protein. The samples were boiled with 100 mL of water in an Erlenmeyer flask at 95°C for 10 min. The eel fillet was divided into three parts: the front, middle, and rear part of the body. Protein profiles from each part were identified using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Bradford assays. Parvalbumin was further purified by ammonium sulfate precipitation. The concentration of protein in the different parts of the eel was not significantly different, whereas the processing treatments (meat with water (F1 extract) and meat without water (F2 extract)) affected protein concentration. Eel meat contained proteins with molecular weights ranging from 10 to 186 kDa. Parvalbumins are highly water-soluble, as their content was reduced in the fillet, but were observed at a high concentration in the water after boiling. Parvalbumins of eel were purified by ammonium sulfate 70-90% with high purity. Interestingly, two different bands were observed in SDS-PAGE, suggesting the presence of a protein variant. The molecular weight of parvalbumin obtained from purification ranged from 10 to 11 kDa, similar to that of other fish.

Detection of fish and mussel DNA in lake sediment cores depends on location, species, and molecular method

AbstractEnvironmental DNA provides an opportunity to track long‐term changes in biological communities in lake ecosystems but the detection of macroorganisms, such as freshwater fish and mussels, in sedimentary DNA (sedDNA) has only been successfully reported in a few studies to date. Factors such as low abundance of the target organisms, sampling location, the molecular approach used, and DNA quantity may influence detection, though studies exploring these factors are lacking. In the present study, sediment cores were collected from a depocenter and nearshore site in a small shallow lake where some historical fish survey data was available. DNA was extracted from the sediment core and analyzed for Anguilla australis (shortfin eel), Echyridella menziesii (freshwater mussel), and Perca fluviatilis (European perch) using droplet digital PCR (ddPCR) and general fish (class Actinopterygii) and macroinvertebrates using metabarcoding. The data from the historical fish surveys (last 20 years) aligned with the molecular data except for a lack of Anguilla dieffenbachii (longfin eel) DNA detection. Generalized additive mixed model analysis showed significantly higher detections in samples from the nearshore compared to depocenter core, which is most likely related to habitat of the target species. Differential detection of target species was likely caused by their ecology and locality. The ddPCR assays were more sensitive (88 ± 3% of samples with positive detections) than metabarcoding (48 ± 10%). However, the metabarcoding enabled the detection of additional fish species. Target species detection was negatively impacted by a reduction in total DNA concentration in older sediments. This research highlights that current molecular techniques used to target fish and mussel sedDNA can result in inconsistent temporal and spatial detection of species, especially in older sediments. We recommend that the methodology and interpretation of sedDNA results need to be considered in the context of species ecology, abundance, and DNA concentrations.

Effects of Indonesian Shortfin Eel (Anguilla bicolor) By-Product Oil Supplementation on HOMA-IR and Lipid Profile in Obese Male Wistar Rats.

The prevalence of people being overweight and obese has increased globally over the past decades. The use of omega-3 fatty acids-a compound usually primarily found in fish oil-has been known to improve the metabolic profile of obese patients. As the demand for eels increases, the number of waste products from the eels increases and creates environmental problems. This study was conducted to investigate the effect of a newly discovered Indonesian Shortfin eel by-product oil supplementation on the Homeostasis Model Assessment-Estimated Insulin Resistance (HOMA-IR) and lipid profiles of obese male (Lee index ≥ 0.3) Wistar rats (Rattus norvegicus). The oil was extracted from waste products (heads). Fifteen obese rats were divided into three groups and were administered NaCl (C), commercial fish oil (CO), and Indonesian shortfin eel by-product oil (EO). All groups had statistically significant differences in total cholesterol, LDL, and triglyceride levels (p < 0.05). The CO and EO group showed a significant decrease in total cholesterol, LDL, and triglyceride after treatment. However, no significant difference was found in HDL levels and HOMA-IR. The supplementation of Indonesian shortfin eel by-product oil significantly improved lipid profile while effectively mitigating environmental challenges.

Alternate Day Feeding as a Cost-effective Strategy for Tank Culture of the Pacific Shortfin Eel Anguilla bicolor pacifica

There is a growing interest in the aquaculture of tropical anguillid eels as an export commodity. However, studies on feeding strategies, and the present demand to reduce feed costs need to be addressed to ensure the economic viability of eel farming. In this study, the effects of daily (DF) and alternate day (ADF) feeding on growth, feed utilization, body composition, blood chemistry, liver and intestinal morphology, and economic viability in the Pacific shortfin eel Anguilla bicolor pacifica were examined. Each feeding group of 30 elvers (166.25 ± 16.23 g mean initial wt) were randomly stocked in triplicate 4 m3 outdoor concrete tanks. These were fed for 155 d with formulated eel powder diet (49.77% crude protein; 10.21% crude lipid) made into a paste. Growth and survival were not significantly different between the two feeding groups. However, feed efficiency was improved in the ADF group, with significantly higher protein efficiency ratio (0.63) than in the DF group (0.39). Feed conversion ratio (FCR) was lower in ADF (3.85) than in the DF group (6.44), resulting in a 40% reduction in total feed consumption. Biometric indices, body proximate composition, and blood chemistry were not significantly affected. Likewise, liver and intestinal morphology showed no apparent alterations between groups. Partial costs-and-returns analysis showed that ADF yielded higher net profit and profit index. These results suggest that feeding on alternate days promote compensatory growth, better feed utilization, and normal physiological condition of A. bicolor pacifica, and reduce feed cost in the rearing process. Therefore, alternate day feeding should be promoted as a sound feed management strategy in the tank culture of tropical anguillid eels.

Application of herbal probiotics in feed on growth and blood profile of elver eels (Anguilla bicolor McClelland, 1844)

Shortfin eel cultivation in Indonesia has shown significant development in aquaculture. However, various challenges still hinder its successful implementation. This study aims to investigate the impact of herbal probiotics on the growth and blood profile of elver eels (Anguilla bicolor). The research was conducted at UPR Mina Mandiri in the Beutong District of Nagan Raya Regency, from August to October 2022This research was conducted at UPR Mina Mandiri, Beutong District, Nagan Raya Regency, from August to October 2022. A Completely Randomized Design (CRD) with five treatment levels and three replications was employed for this study. The treatments consisted of herbal probiotics added to the eels' feed: 0, 15, 20, 25, and 30 ml/kg. The data obtained from the experiment were subjected to an analysis of variance (ANOVA) to assess the significance of the results. ANOVA test results show that probiotics significantly affect survival rate, absolute weight growth, specific weight rates, feed efficiency, and the elver eel blood profile (hemoglobin, erythrocytes, and leukocytes). (P0.05). Duncan's advanced test revealed significant differences in the growth parameters and blood profiles among the various treatments. Treatment B, which utilized a dosage of 15 ml/kg of feed, displayed the most favorable outcomes. It achieved a survival rate of 93.33%, absolute weight growth of 2.69 grams, a specific growth rate of 1.73%, and a feed efficiency of 48.56%. Additionally, the blood profile measurements for treatment B were as follows: hemoglobin levels ranged from 9.53 to 9.73 g/dl, erythrocyte count ranged from 1.12 to 1.23 x 103 cells/mm3, and leukocyte count ranged from 120 to 133 x 103 cells/mm3.Keywords:blood profilefish healthgrowthshortfin eels probiotics

Feeding frequency on survival, growth, blood glucose of glass eel, Anguilla bicolor bicolor cultured in a recirculating aquaculture system

Indonesian shortfin eel, Anguilla bicolor bicolor is one of the eel species that high market demand both for local and export. Feeding frequency is an important that related to production for culture. The purpose of this experiment is to determine the optimal feeding frequencies on survival and growth of shortfin eel at glass eel to elver stages cultured in a recirculating aquaculture system. Four treatments of different feeding frequencies and three replicates each were performed. The treatments were as followed A) 1 time a day; B) 2 times a day; C) 3 times a day; and D) 4 times a day. The result showed that the feeding frequency affect the survival, length and weight growths, and glucose value. The best of survival rate (82.61±3.15%), weight (1.91±0.28 g) and length (10.64±0.45cm) found at feeding frequency 3 times a day compared to the others (P<.0.05). Blood glucose value increases with increasing feeding frequency. Water quality such as dissolved oxygen (DO), temperature and pH were within the optimal range. Three times a day of feeding frequency is recommended for applying on glass eel culture in a recirculating aquaculture system.

Configuration of gut bacterial community profile and their potential functionality in the digestive tract of the wild and cultivated Indonesian shortfin elver-phase eels (Anguilla bicolor bicolor McClelland, 1844).

This study aimed to explore the bacteria present in the digestive tracts of wild and cultivated Indonesian shortfin eel during the elver phase. The eel has high export potential due to its vitamin and micronutrient content, but slow growth and vulnerability to collapse in farm conditions hinder its cultivation. The microbiota in the eel's digestive tract is crucial for its health, particularly during the elver phase. This study used Next Generation Sequencing to analyze the community structure and diversity of bacteria in the eels' digestive tracts, focusing on the V3-V4 regions of the 16S rRNA gene. Mothur software was used for data analysis and PAST v.3.26 was used to calculate alpha diversity. The results showed that Proteobacteria (64.18%) and Firmicutes (33.55%) were the predominant phyla in the digestive tract of cultivated eels, while Bacteroidetes (54.16%), Firmicutes (14.71%), and Fusobacteria (10.56%) were predominant in wild eels. The most prevalent genera in cultivated and wild elver were Plesiomonas and Cetobacterium, respectively. The microbiota in the digestive tract of cultivated eels was diverse despite uneven distribution. The KEGG database analysis revealed that the primary function of the microbiome was to facilitate the eel's absorption of nutrients by contributing significantly to the metabolism of carbohydrates and amino acids. This study's findings can aid in assessing eel health and improving eel farming conditions.

Effect of size grading on growth of yellow Pacific shortfin eel (Anguilla bicolor pacifica).

Heterogeneous growth, which is common among farmed fish, can be remedied by size grading. This study focused on whether the size grading process, which is commonly practiced in aquaculture, improves the subsequent growth performance of the Pacific shortfin eel Anguilla bicolor pacifica. Eels [338.70 ± 4.70 mm total length (TL) and 84.93 ± 1.87 g body weight (BW)] were initially reared for 60 days (pre-size grading period) and manually divided into three size groups: small (≤115 g), large (>150 g) and mixed (>115 g but <170 g), all maintained at a density of 5 kg m-3 and reared until day 150 (size grading period). After size grading, mean BW and TL at harvest significantly differed in all eel groups, suggesting growth was size specific. Nonetheless, at day 150, except for biomass, size grading had no significant effect on growth and survival, coefficient of variation of length and weight, and Fulton's condition factor. Large eels had a significantly higher feed intake than mixed or small eels, whereas feed efficiency did not differ among eel groups. Results suggest that size grading promotes size-specific growth but did not improve the overall growth performance of yellow stage of A. bicolor pacifica.

Laboratory-based comparison of screening materials for excluding juvenile freshwater fishes from New Zealand water intakes

ABSTRACT Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values.

Molecular Identification of Elvers (&lt;I&gt;Anguilla&lt;/I&gt; spp.) from River Estuaries in Central Java, Indonesia Using DNA Barcoding Based on &lt;I&gt;mt&lt;/I&gt;DNA CO1 Sequences

Highlight Research The elvers of Anguilla were identified through the morphological and molecular markers The result of morphological and molecular identification is different The molecular identification helps to confirm the morphological identification Based on this study molecular identification of the elvers of Anguilla found in river estuaries of Central Java is Anguilla bicolor bicolor Abstract An inventory of the presence and diversity of Anguilla spp. needs to be carried out as a basis for sustainable resource management. Conventional techniques based on morphological characteristics—are often less effective considering the morphological characteristics of Anguilla spp. are very identical and not so many can be observed, especially at the young eel stage. DNA-based molecular identification can be a way to determine diversity and phylogeny for conservation and inventory purposes. This research aimed to determine the diversity and phylogeny of Anguilla spp. obtained at the estuaries of Serayu River in Cilacap, Luk Ulo River in Kebumen, and Jali River in Purworejo in Central Java, Indonesia. A total of 10 samples were taken from each research location were analyzed morphologically, then it is known that there are 4 morphologically different samples at each research location so that a total of 12 samples were taken for molecular analysis. MEGA was used to construct the phylogenetic trees via Neighbour Joining (NJ) algorithms using the Kimura 2-parameter model with uniform rates and obtained by 1000 bootstraps replication. There are four species of Anguilla spp. identified morphologically, namely Anguilla bicolor bicolor, Anguilla bicolor pacifica, Anguilla obscura, and Anguilla australis. The species of Anguilla spp. that is molecularly identified is Anguilla bicolor bicolor with an identity percentage of &gt; 98%. All samples are also known to be related to Anguilla bicolor bicolor identified in other countries.

Lipoprotein receptors in ovary of eel, Anguilla australis: molecular characterisation of putative vitellogenin receptors

Lipoprotein receptors, including low-density lipoprotein receptor (LDLr) relatives (Lrs) and LDLr-related proteins (Lrps), belong to the LDLr supergene family and participate in diverse physiological functions. In this study, novel sequences of lr and lrp genes expressed in the ovary of the short-finned eel, Anguilla australis, during early gonadal development are presented. The genes encoding the LDLr-like, Lrp1-like, Lrp1b-like, Lrp3, Lrp4-like, Lrp5-like, Lrp6, Lrp10, Lrp11, Lrp12-like, and Lr11-like proteins were found and identified by sequence and structure analysis, in addition to phylogenetic analysis. Genes encoding proteins previously implicated in follicle development and vitellogenin (Vtg) uptake in oviparous vertebrates were also identified, i.e. lr8 (including lr8 + and lr8- variants) and lrp13; their identification was reinforced by conserved synteny with orthologues in other teleost fish. Compared to other lr/lrp genes, the genes encoding Lr8 + , Lr8-, and Lrp13 were highly expressed in ovary during early development, decreasing as oocyte development advanced when induced by hypophysation. Furthermore, lr8 + , lr8-, and lrp13 were dominantly expressed in the ovary when compared with 17 other tissues. Finally, this study successfully detected the expression of both lr8 variants, which showed different expression patterns to those reported in other oviparous vertebrates and provided the first characterisation of Lrp13 in Anguilla sp. We propose that lr8 + , lr8-, and lrp13 encode putative Vtg receptors in anguillid eels.

Comparing the performance of three common species distribution modelling frameworks for freshwater environments through application to eel species in New Zealand

Globally, many freshwater species are depleting and require population-level assessments. Many species distribution modelling frameworks are available for such assessments, but comparisons are needed to understand their predictive performance under different settings. K-fold cross-validation techniques were employed to compare the performance of three commonly used frameworks: machine learning, spatiotemporal modelling, and Gaussian process (GP) modelling. Through application to New Zealand populations of longfin eel ( Anguilla dieffenbachii) and shortfin eel ( Anguilla australis), area under the receiver operating characteristic curve (AUC) and true skill statistic (TSS) model performance metrics were estimated. All modelling frameworks produced approximately consistent distribution maps but differed in predictive performance. AUC and TSS results indicated that model predictions from the spatiotemporal modelling framework were the most accurate, followed by GP modelling. However, all modelling frameworks performed similarly when training and test data were spatially independent. In addition to having the best predictive performance, the spatiotemporal modelling framework showed the greatest promise for advancement in population-level assessment and is therefore recommended. The results are useful for freshwater ecologists and resource managers to make informed decisions on the appropriateness of a modelling framework for their research objective.

Safety, Adherence, Enzymatic Activities, and Application Effects of Oral Probiotic Candidates for Shortfin Eel (Anguilla bicolor bicolor)

Highlight Research The shortfin eel elver bicolor bicolor was tested for the safety of Enterobacter sp. JC05, Lactococcus sp. JAL37, and Bacillus sp. PCP1 The ability of bacterial strains to adhere to epithelial cells of shortfin eel epithelial cells was demonstrated The bacterial strains' proteolytic, cellulolytic, and lipolytic activities were detected Oral administration of the bacterial cocktail lowered overall viable bacterial count but did not affect the shortfin eel's intestinal histological characteristics Abstract Aquaculture of the shortfin eel (Anguilla bicolor bicolor) has been plagued by low survival and growth due to the low tolerance to water quality and feed. The microbiota and shape of the fish intestinal tract influence the immune and digestive systems. The use of bacterial probiotics is fascinating to enhance the digestion system. This study aimed to characterize bacterial probiotic candidates' safety and potential probiotic features for shortfin eel (A. bicolor bicolor) aquaculture. The safety, adherence, and enzymatic activity of three bacterial strains (Bacillus sp. PCP1, Lactococcus sp. JAL 37, and Enterobacter sp. JC05) were investigated. An oral application test was performed on shortfin eel (n=880, 15 g) every four days with 0, 3x103, 3x105, and 3x107 CFU/g diet dosages in quadruplicates for two months. At the end of the experiment, total cultivable bacteria and intestinal morphology were assessed. Based on the hemolytic test and intraperitoneal injection, the bacterial strains were considered harmless. In an in vitro investigation, the bacteria attached to shortfin eel intestinal epithelial cells. An agar diffusion method validated the proteolytic, lipolytic, and cellulolytic activities. In vivo feeding tests with the bacterial cocktail lowered the total viable bacteria in the gut while preserving the gut histology. Bacterial strains of the present study are potential probiotic candidates for shortfin (A. bicolor bicolor) aquaculture.

Sperm quality of artificially matured shortfinned eel is not affected by human chorionic gonadotropin dose and route of administration.

BackgroundAcquisition of high quality sperm is key to the artificial propagation of eels in captivity, but fertility drugs are expensive and repeated handling is stressful to the fish. An interrupted treatment regime (an initial hormone injection to stimulate spermatogenesis, followed several weeks later by weekly booster injections to induce sperm maturation) for acquisition of sperm in captive male eels has promise for high sperm quality on the one hand, and animal welfare benefits on the other. To further develop this approach for shortfinned eel, Anguilla australis, we evaluated the efficacy of (i) different initial doses of human chorionic gonadotropin (hCG) and (ii) route of administration.MethodsMale eels were artificially induced to mature with a single injection of 0, 250, 500 or 1,000 IU/fish of hCG, administered either intramuscularly (IM) or intraperitoneally (IP). Sperm maturation was induced with 150 IU hCG/fish from week 5 onwards and sperm collected for evaluation of quality by computer-assisted sperm analysis.ResultsControl males did not mature and hence, sperm could not be retrieved and analysed, but all other treatments were effective in inducing testicular maturation. Milt volume tended to be higher for fish injected IM compared to those injected IP, whereas hCG dose had no effect. Conversely, the concentration of spermatozoa tended to be higher for several sperm collection time points in IP-injected than in IM-injected fish. Sperm quality, represented by percent motility, percent progressive motility and curvilinear velocity, was equal in fish given an initial dose of 250 IU hCG to those given higher initial doses of hCG.ConclusionsWe recommend that an initial dose of 250 IU hCG/fish be administered to induce spermatogenesis in male A. australis, and, after a period of 4–5 weeks, weekly booster injections of ∼150 IU hCG/fish be administered in the day prior to sperm collection; both routes of administration (IM or IP) are equally effective. We contend that an interrupted treatment regime has notable benefits for induced maturation in male anguillids, as it reduces fish handling and manipulation and reduces the resources required to produce high quality sperm.

Optimised protocol for the extraction of fish DNA from freshwater sediments

Abstract Monitoring fish is necessary for understanding population dynamics, tracking distribution patterns and evaluating conservation efforts. Molecular techniques targeting environmental DNA (eDNA) are now considered effective methods for detecting specific species or characterising fish communities. The analysis of DNA from lake‐surface sediments (sedDNA) can provide a time‐integrated sampling approach which reduces the variability sometimes observed in water samples. However, studies of sedDNA have had varying success in detecting fish. The present study aimed to determine the most effective extraction method for recovering fish DNA from lake‐surface sediments. A literature review was undertaken to identify DNA extraction methods used previously on aquatic sediments targeting aquatic and terrestrial animals. Five methods with various modifications were tested to establish their ability to desorb extracellular DNA. Based on these results, two methods were selected and optimised, and the recovery of fish sedDNA characterised using droplet digital PCR assays targeting eel and perch (Anguilla australis, Anguilla dieffenbachii, Perca fluviatilis). A range of sediment masses (0.25–20 g) were assessed to establish the optimal amount required to accurately assess fish sedDNA. The DNA extraction methods found to be most effective at recovering extracellular DNA spiked into small sediment masses (0.25 g) were the DNeasy PowerSoil DNA Isolation Kit (QIAGEN), and the ABPS protocol which involved an initial alkaline buffer extraction followed by the PowerSoil extraction kit. For larger sediment masses (&gt;0.25 g) the ABPS protocol or the DNeasy PowerMax Soil Kit (QIAGEN) with an additional ethanol DNA concentration step (PMET protocol) yielded the highest concentrations of target genes across a range of lake sediments. Larger sediment masses (≤20 g was tested) increased the likelihood of detection of fish in sedDNA. Optimisation of the ABPS protocol was required (65°C incubation temperature, pooling of multiple PowerSoil extractions) to overcome technical challenges related to co‐precipitation of organic content in lake‐surface sediments. This optimised ABPS protocol was called the “Lakes ABPS protocol”. We recommend the use of the Lakes ABPS protocol as it is cheaper than the PMET protocol. Additionally, after the first extraction step, the process can be automated on a DNA extraction robot, allowing for higher sample throughput. A mass of 10 g is suggested, although higher detection is achieved with more sediment, a suite of challenges, such as co‐precipitation of organic content, are encountered when the amount is increased. This study highlights the complexity of the extraction and detection of fish sedDNA from lake sediment, especially when it has a high organic content. We have optimised a DNA extraction method to overcome some of these complexities that can be applied to a wide range of lake sediments.