A comparison between water exchange and settling tank as a method for suspended solids management in intensive biofloc technology systems: effects on shrimp (Litopenaeus vannamei) performance,water quality and water use

Biofloc systems rely on microbial processes in the water column to recycle animal waste products, reducing the need for water exchange. These increases biofloc concentration in the water and some form of removal is needed. An experiment was carried out to evaluate two management practices to control biofloc in Litopenaeus vannamei culture. Six tanks (48 m³) were divided into two treatments: water exchange and solid settler. Shrimp were stocked at 164 shrimp m^?2 and with 0.67 g of weight. After 61 days, shrimp under solid settler treatment demonstrated mean weight of 12.7 ± 0.5 g with survival of 73.8 ± 1.4%, and those under water exchange had a final weight of 10.1 ± 0.2 g and survival rate of 57.8 ± 11.1%. Total suspended solids did not differ between the treatments: 326.8 ± 24.9 mg L^?1 for water exchange and 310.9 ± 25.3 mg L^?1 for solid settlers. Settleable solids and productivity/respiration ratio was higher (P < 0.05) in water exchange treatment, indicating differences in physical and biological characteristics of bioflocs. Solids removal method influenced the water use, in which 1150 ± 249 L of water was necessary to produce one kilogram of shrimp using water exchange strategy, and 631 ± 25 L kg^?1 with the use of settlers. Our results indicate that continuous operation of settlers can reduce variability in solids characteristics and water quality variables such as ammonia. Both strategies are efficient in controlling biofloc concentrations of the water; however, settlers can reduce water use and improve shrimp production.     

Phylogenetic analysis of intestinal bacteria of freshwater salmon Salmo salar and sea trout Salmo trutta trutta and diet

The microbial diversity of culturable intestinal microflora of wild freshwater salmonid fishes salmon Salmo salar and sea trout Salmo trutta trutta juveniles (0+ years old) from the same environmental conditions were investigated by means of molecular identification techniques and analysis of diet. Significant differences in the intestinal microbial diversity were observed in different fish species. The predominant group in the intestinal tract of the salmon comprised representatives of the Enterobacteriaceae family (23%), Plesiomonas (19.2%) and Carnobacterium (15.3%). Predominant microbiota in sea trout intestinal tract were Enterobacteriaceae (52%), Aeromonas (22%) and Pseudomonas (14%). The results show that Enterobacteriaceae were predominant in the intestinal tract of the salmon and the sea trout juveniles raised on diets of different compositions. However, molecular identification of the intestinal microbiota at the species or genus level revealed differences in these fish species. Bacteria in the hindgut of salmon included Pragia and Serratia. However, bacteria in the gut contents of sea trout from the Enterobacteriaceae family were Buttiauxella, Enterobacter, Moellerella, Pantoea, Rahnella and Tiedjeia arctica. A novel phylotype of T. arctica is harbored in the intestinal tract of wild salmon, and may correspond to a previously undescribed species.     

Replacement of fish oil with vegetable oils in diets for jundiá (Rhamdia quelen Quoy and Gaimard 1824): effects on performance and whole body fatty acid composition

The jundiá (Rhamdia quelen) is a siluriform with great potential for aquaculture in South America. Fish oil is a raw material in diets for fish. However, the fisheries that provide fish oil have reached their limit of sustainability. Thus, the use of alternative sources for this ingredient is primordial. The aim of this study was to evaluate the performance and body composition of the jundiá fed with different sources of the vegetable oils. Jundiá (1.0±0.2 g) were fed for 31 days with five isonitrogenous (37%) and isoenergetic (19 kJ g^?1) diets, in which the following oils were added: 50 g kg^?1 corn oil (CO), 50 g kg^?1 fish oil (FO), 50 g kg^?1 linseed oil (LO), 33.4 g kg^?1 fish oil and 16.7 g kg^?1 linseed oil (1/3LO), 16.7 g kg^?1 fish oil and 33.4 g kg^?1 linseed oil (2/3LO). The performance did not show differences between treatments. The final fatty acid profile and n‐3/n‐6 ratio of the fish were highly influenced by the diet. Fish‐fed diets with linseed and/or fish oil showed superior n‐3/n‐6 ratios to the minimal recommended by the World Health Organization; whereas fish fed diets with corn oil showed an inferior value. Albeit in the present study the commercial size of fish was not attained, these results show a clear tendency. The desaturation/elongation capacity was evidenced, in this species, for the first time. Linseed oil can be utilized as a substitute for fish oil in diets of jundiá without affecting their performance and for producing good‐quality fish. However, more studies are necessary to confirm these results for commercial size.     

Effect of environmental factors on the fatty acid profiles and physicochemical composition of oysters (Crassostrea gasar) in Amazon estuarine farming

The objective of this study was to evaluate the effect of environmental factors on the fatty acid profiles and physicochemical composition of Crassostrea gasar cultured in two locations with differences in salinity and precipitation gradients. The study period was divided into four seasonal divisions—the rainy–dry transition period, the dry season, dry–rainy transition and the rainy season. The salinity, pH and temperature were measured at each site during specimen collection. A total of 712 oyster samples were used for fatty acid profiling and physicochemical analysis. Salinity and precipitation were the environmental parameters that influenced the fatty acid profile and physicochemical characteristics of oysters. C. gasar exhibited excellent values of n3 polyunsaturated fatty acids (DHA, EPA and eicosatrienoic), with a predominance of these acids during periods of higher precipitation. Variations in precipitation and salinity resulted in significant differences in oyster nutritional characteristics. Oysters grown in Amazonian estuaries can be considered nutritious throughout the year, with better conditions during the rainy season.     

Mechanisms of N2O and NO production in the soil profile of a drained and forested peatland, as studied with acetylene, nitrapyrin and dimethyl ether

 Acetylene, dimethyl ether (DME) and 2-chloro-6-trichloromethyl pyridine (nitrapyrin) were used as inhibitors to study the contributions of nitrification and denitrification to the production of N₂O and nitric oxide (NO) in samples taken from the soil profile of a peatland drained for forestry. Acetylene and DME inhibited 60–100% of the nitrification activity in field-moist samples from the 0–5 cm and 5–10 cm peat layers, whereas nitrapyrin had no inhibitory effect. In the 0–5 cm peat layer the N₂O production could be reduced by up to 90% with inhibitors of nitrification, but in the 5–10 cm peat layer this proportion was 20–30%. All the inhibitors removed 96–100% of the nitrification potential in peat-water slurries from the 0–5 cm peat layer, but the 5–10 cm layer had a much lower nitrification activity, and here the efficiency of the inhibitors was more variable. Litter was the main net source of NO in the peat profile. NO₃ ^– production was lower in the litter layer than in the peat, whereas N₂O production was much higher in the litter than in the peat. Denitrification was the most probable source of N₂O and NO in the litter, which had a high availability of organic substrates. Received: 14 July 1997     

Simple and rapid field tests for brucellosis in livestock

Four simple and rapid field tests for the serodiagnosis of brucellosis in cattle, goat, sheep and swine were developed. The performance of the assays was investigated using serum samples collected in Portugal from animals originating from herds with a defined sanitary status with respect to the presence of brucellosis. The sensitivity calculated for the bovine, caprine, ovine and swine Brucella lateral flow assays based on results obtained for samples collected from animals with culture confirmed brucellosis was 90%, 100%, 90% and 73%, respectively. None of the samples from animals from herds free of brucellosis reacted in the flow assays indicating a high specificity. However, as expected, some degree of reactivity was observed when testing selected serum samples that reacted non-specific in reference tests for brucellosis.     

Effects of 5 years of digestate application on biomass production and quality of cocksfoot (Dactylis glomerata L.)

Anaerobic digestion of biomass produces biogas for combustion and also provides a residual digestate. Although sometimes regarded as a waste product, the nutrient‐rich chemical composition of digestate makes it a potential organic fertilizer for agriculture. The goal of this study was to evaluate the effectiveness of digestate as a fertilizer on the biomass yield and chemical composition of cocksfoot (Dactylis glomerata L.). In a 5‐year small‐plot field experiment digestate fertilization treatments supplying 90, 180, 270, 360 and 450 kg N ha^?1 were compared with untreated plots and plots fertilized with 180 kg N ha^?1 of mineral N fertilizer. Swards fertilized with digestate produced higher biomass yield compared with the control. The same rate of nitrogen fertilizer (180 kg N ha^?1) supplied as digestate and from mineral fertilizers gave similar results on biomass yield. Herbage in swards fertilized with digestate contained less nitrogen, but the C:N ratio was much more suitable for biogas production. Digestate fertilization resulted in higher concentrations of cellulose and hemicellulose in biomass and lower contents of the inhibitors of anaerobic digestion—sulphur, calcium, magnesium and phosphorus—compared with those of swards receiving mineral fertilizers.     

Dietary supplementation of yeast (<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>) improves growth,stress tolerance,and disease resistance in juvenile Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

The yeast Saccharomyces cerevisiae is one of the commonest probiotics incorporated in aquafeeds. An 84-day feeding trial was conducted to evaluate the effects of varying dietary inclusions of S. cerevisiae, 0% (control), 3% (YF3), 5% (YF5), and 7% (YF7), on growth, stress tolerance, and disease resistance in juvenile (body mass ~?21 g) Nile tilapia (Oreochromis niloticus). Fish were randomly distributed in groups of 20 into 12 1-m³ hapas and fed isoenergetic (~?17 kJ g^?1 gross energy) and isonitrogenous (~?300 g kg^?1 crude protein) diets at 3% of their bulk weight daily. Specific growth rates were significantly higher for the yeast-fed fish (0.77–0.78% day^?1) than for the control fish (0.60% day^?1) and resulted in significantly higher mean final weights for the yeast-treated groups. Protein and lipid retention efficiencies were also significantly higher in the yeast-fed fish than in the control group. In subsequent stress challenge trials, the yeast-fed fish had greater tolerance to acute heat as well as hypoxia exposure than the control fish. Survival rates of the yeast-treated groups following sudden exposure to elevated water temperature (40 °C) ranged from 82.5 to 100% compared to 15% for the control. Mean survival rates following a 24-h hypoxia exposure were also generally significantly higher for the yeast-fed fish. The probiotic groups recorded a relative percent survival (RPS) of 75% after a 14-day Aeromonas hydrophila infection challenge. The results of this study indicate that S. cerevisiae as an additive in Nile tilapia diets has beneficial impacts on growth, stress tolerance, and disease resistance.