Enhancing rotifer Brachionus calyciflorus population growth with commercial probiotics

The effect of a commercial probiotic (NanoCrusta, Altacrusta, Mexico City, Mexico) on the growth performance of Brachionus calyciflorus Pallas, 1766, was evaluated. In a first approach, probiotics were supplied in four densities (2.0 × 10³, 1.1 × 10⁵, 2.1 × 10⁵ and 2.1 × 10⁶ cells/ml), alone and in combination with Chlorella vulgaris (1 × 10⁶ cells/ml). The test rotifer did not grow on the probiotic alone. However, when probiotics + C. vulgaris were added, the maximum densities (D_max; ind/ml) and population growth rates (r) observed were higher. In the second experiment, probiotics were supplied at five higher densities (2.1 × 10⁶, 4.2 × 10⁶, 8.5 × 10⁶, 1.7 × 10⁷ and 3.4 × 10⁷ cells/ml) with C. vulgaris and a control treatment with only C. vulgaris (probiotic‐free). Treatments supplied with probiotics between 2.1 × 10⁶ and 1.7 × 10⁷ cells/ml showed significantly higher D_max and r than the control treatment. The results showed a positive effect of probiotic bacteria when supplied with C. vulgaris. The best outcome showed a D_max 2.16 times and an r 1.63 times higher than the density of the control treatment. Growth rates were higher in the treatments with probiotics compared to the control. We conclude that application of NanoCrusta is feasible to improve B. calyciflorus production, but the effects need to be tested in larger scales.     

Assessment of dietary lipid sources in tropical gar,Atractosteus tropicus larvae: Growth parameters and intermediary lipogenic gene expression

Five experimental diets containing different lipid sources, fish oil (D1), soybean lecithin (D2), corn oil (D3), canola oil (D4) and olive oil (D5), were evaluated in Atractosteus tropicus larvae for the relative gene expression of the enzymes fatty acid synthase (fas), acetyl‐CoA carboxylase 1 (acc1) and carnitine palmitoyltransferase 1C (cpt1c), in addition to their effects on larval growth, survival and cannibalism during a 30‐day feeding trial. Higher growth and survival were obtained in treatments D1 and D2, and lower performance in diets D3, D4 and D5. The highest levels of expression of fas and acc1 occurred in larvae fed with D1, which contained high amounts of n‐3 long‐chain polyunsaturated fatty acids (LC‐PUFA), mainly DHA and EPA FA are regulators of lipogenesis. The higher cpt1c expression in plant‐based diets is attributed to the fact that these diets are rich in α‐linolenic acid (ALA) and low DHA, EPA and ARA levels that favour ß‐oxidation. In conclusion, the diets with fish oil (D1) and soybean lecithin (D2) were the best treatments for larval growth, survival and cannibalism and thus appear to meet both lipid and energy requirements of A. tropicus larvae, meanwhile the use of vegetable oils influences the expression of intermediary lipogenic genes.     

Laboratory and on‐farm evaluation of low‐cost salt mixtures for use during salinity acclimation and the nursery phase of Pacific white shrimp (Litopenaeus vannamei)

The current study evaluates the efficacy of a low‐cost salt mixture (LCSM) to replace expensive reconstituted sea salt (RSS) in the salinity acclimation and nursery phase of Pacific white shrimp under laboratory and farm conditions. LCSM was formulated to yield sodium, potassium, calcium and magnesium concentrations closely comparable to that of diluted seawater. Laboratory‐based nursery trials were conducted at 2, 6 and 15 g/L salinities, incrementally replacing RSS with LCSM (25%, 50%, 75% and 100%) at four replicates per treatment. Thirty postlarvae were reared for 7 days in 24‐L aquaria during the 2 and 6 g/L trials, while the nursery trial for 15 g/L salinity was conducted for 21 days with 400 postlarvae stocked in 150‐L tanks. On‐farm evaluation of LCSM was carried out in two tank‐based systems installed on levees adjacent to shrimp production ponds. RSS was incrementally replaced with LCSM (0%, 50%, 75% and 100%) and 100 postlarvae stocked into each 800‐L tank. Salinity acclimation was done from 30 g/L to 6 or 1.5 g/L within 2–3 days by pumping water from adjacent shrimp production ponds. Following salinity acclimation, the S4 system maintained flow‐through at 1.5 g/L, while N10 system was maintained static at 6 g/L salinity. At the conclusion, no significant differences were observed for either survival or growth of shrimp postlarvae between RSS and LCSM treatments at all salinities examined. Results reflect the potential use of LCSM to replace RSS, which could be an excellent solution to bring down the cost of production in inland shrimp aquaculture.     

Development of a method for live octopus (Octopus vulgaris) transportation for long distance at high densities

The development of new octopus‐based products with a growing economic value ensures the commercial interest of this species, making live octopus export an activity of great interest. The aim of this study was to develop a method for long‐distance transportation of live octopus at high densities. The system was composed by 220‐L tanks with cooling and aeration, where the animals were kept separated from each others. The water temperature was maintained at 10°C, after a decreasing of 1°C/hr. Live octopus transportation was tested for 48 hr at two densities: 50 kg/m³ and 100 kg/m³. During this period, water parameters were monitored. Stress response was evaluated through the analysis of haemolymph, muscle and brain tissues. No mortality was registered after 48 hr for both treatments. In all trials, water quality remained within the normal limits in both densities; there was, however, a significative increase of ammonia levels in the water. Ammonia, dopamine and Hsp70 levels were analysed in the beginning and at the end of the experiment for both densities; however, no significant differences were found among them. In general, this system seems to be a viable solution for live octopus 48‐hr transportation at a density of 100 kg/m³.     

Development and testing of a Bayesian population model for the bigeye thresher shark,Alopias superciliosus,in an area subset of the western North Pacific

A Bayesian population modelling tool integrating separable virtual population analysis, per‐recruit models and age‐structured demographic analysis was developed for the bigeye thresher Alopias superciliosus (Lowe) population in an area subset of the western North Pacific. The mortality rates for years 1989–2016 were estimated, various biological reference points and associated risks of decline were also estimated, and alternative harvest strategies for the stock were evaluated. Estimates of the posterior mean of fishing mortality for bigeye thresher shark suggest fishing pressure has been high in recent years (2011–2016). The estimated population growth rate (λ) (without fishing) obtained from age‐structured demographic model was relatively low (λ = 1.01 per year; 95% confidence intervals of 1.00 and 1.03 per year). Risk analyses revealed that only low levels of fishing pressure (10% of the current fishing pressure) over a wide range of ages could maintain a relatively low risk of population decline for bigeye threshers. Sensitivity testing indicated that the model is robust to prior specification. The developed framework could be used as an assessment tool to evaluate the risk of decline for other widely distributed pelagic shark species where insufficient catch and effort data are available.     

Boom‐bust like dynamics of invasive black bullhead (Ameiurus melas) in Lake Sava (Serbia)

The life‐history traits and population dynamics of the black bullhead Ameiurus melas (Rafinesque) were studied monthly from August 2009 to December 2012 in Lake Sava in Belgrade (Serbia). This period included a mass mortality event in May 2011 and subsequent population recovery during 2012. Available evidence suggests the mass mortality was caused by European catfish virus that only affected the black bullhead. Changes in key life‐history traits and the recovery potential (increase in catch‐per‐unit‐effort, doubling of young‐of‐the‐year to adult ratio, earlier maturation and increased fecundity) following the mass mortality event suggest population resilience typical of a recurring boom‐bust pattern and demonstrate the species’ capacity to recover rapidly and re‐establish following disturbance. Repeated systematic mass removals of both juveniles and adults (using fyke nets) will be required if future fishery management measures aimed at limiting the population size are to be effective.     

Amino acid changes in the capsid protein of a reassortant betanodavirus strain: Effect on viral replication in vitro and in vivo

Betanodavirus reassortant strains (RGNNV/SJNNV) isolated from Senegalese sole harbour an SJNNV capsid featuring several changes with respect to the SJNNV‐type strain, sharing three hallmark substitutions. Here, we have employed recombinant strains harbouring mutations in these positions (r20 and r20 + 247 + 270) and have demonstrated that the three substitutions affect different steps of the viral replication process. Adsorption ability and efficiency of viral attachment were only affected by substitutions in the C‐terminal side of the capsid. However, the concurrent mutation in the N‐terminal side seems to slightly decrease these properties, suggesting that this region could also be involved in viral binding. Differences in the intracellular and extracellular production of the mutant strains suggest that both the C‐terminal and N‐terminal regions of the capsid protein may be involved in the particle budding. Furthermore, viral replication in sole brain tissue of the mutant strains, and especially double‐ and triple‐mutant strains, is clearly delayed with respect to the wt strain. These data support previous findings indicating that the C‐terminal side plays a role in virulence because of a slower spread in the fish host brain and suggest that the concurrent participation of the N‐terminal side is also important for viral replication in vivo.     

Biocontrol of saprolegniosis in rainbow trout (Oncorhynchus mykiss Walbaum) using two bacterial isolates (LE89 and LE141) of Pseudomonas fluorescens

The probiotic activity of 15 bacterial isolates that inhibit Saprolegnia parasitica in vitro was tested for the biocontrol of saprolegniosis in rainbow trout (Oncorhynchus mykiss Walbaum), adding the bacteria to tank water for 14 days at a concentration of 10⁶ bacteria ml^?1 water. Pseudomonas fluorescens LE89 and Pseudomonas fluorescens LE141 were effective in controlling experimental infection with S. parasitica since of the fish treated with LE89, 24.5% ± 16.27% (p < 0.05) became infected, as did 42.8% ± 8.41% (p < 0.05) of those treated with LE141. Given their protective effect when administered in water, their effect was also studied when administered in feed before and after experimental infection. Both bacterial isolates survived low pH levels and the action of bile, grew in skin and intestinal mucus, were resistant to several antibiotics and survived in feed; however, neither of the two isolates prevented S. parasitica infection when administered in feed.     

Multilocus sequence typing detects new Piscirickettsia salmonis hybrid genogroup in Chilean fish farms: Evidence for genetic diversity and population structure

Piscirickettsia salmonisis the causative bacterial pathogen of piscirickettsiosis, a salmonid disease that causes notable mortalities in the worldwide aquaculture industry. Published research describes the phenotypic traits, virulence factors, pathogenicity and antibiotic‐resistance potential for various P. salmonisstrains. However, evolutionary and genetic information is scarce for P. salmonis. The present study used multilocus sequence typing (MLST) to gain insight into the population structure and evolution of P. salmonis. Forty‐two Chilean P. salmonisisolates, as well as the type strain LF‐89^T, were recovered from diseased Salmo salar, Oncorhynchus kisutchand Oncorhynchus mykissfrom two Chilean Regions. MLST assessed the loci sequences of dnaK, efp, fumC, glyA, murG, rpoD and trpB. Bioinformatics analyses established the genetic diversity among P. salmonis isolates (H = 0.5810). A total of 23 sequence types (ST) were identified, 53.48% of which were represented by ST1, ST5 and ST2. Population structure analysis through polymorphism patterns showed few polymorphic sites (218 nucleotides from 4,010 bp), while dN/dS ratio analysis indicated purifying selection for dnaK, epf, fumC, murG, and rpoD but neutral selection for the trpB loci. The standardized index of association indicated strong linkage disequilibrium, suggesting clonal population structure. However, recombination events were detected in a group of seven isolates. Findings included genogroups homologous to the LF‐89^T and EM‐90 strains, as well as a seven‐isolate hybrid genogroup recovered from both assessed regions (three O. mykiss and four S. salar isolates). The presented MLST scheme has comparative potential, with promising applications in studying distinct P. salmonis isolates (e.g., from different hosts, farms, geographical areas) and in understanding the epidemiology of this pathogen.