Transmission mechanisms of fish electric signals

Fishes utilize electric signals for passive and active electrolocation and communication at night in murky water. To our knowledge, the mechanism of transmission of fish electric signals through water has not been addressed. In such a medium, the transmission of electrical signals can occur by movement of ions (ion conduction) under the influence of a generated electric field, or through its perturbation by nearby objects that have electric permittivity different than water. This latter property refers to the ability of a medium to resist the formation of electric fields with no involvement of ion transport. In this study, we discuss the relevance of each mechanism in the context of previous reports on transmission of signals by electric fishes in water environments.     

Multiplex PCR for genotyping Flavobacterium columnare

Recent research has identified four distinct genetic groups among isolates of Flavobacterium columnare through multilocus phylogenetic analyses; however, there are no quick methods to determine the genotype of an isolate. The objective of this research was to develop a multiplex PCR to rapidly genotype F. columnare to genetic group. Comparative bacterial genomics was used to identify regions in the genomes unique to each genetic group, and primers were designed to specifically amplify different sized amplicons for each genetic group. The optimized assay was demonstrated to be specific for each genetic group and F. columnare, and no specific amplicons were generated using gDNA from a panel of other Flavobacterium spp. and bacterial fish pathogens. The analytical sensitivity of the assay ranged from 209 to 883 genome equivalents depending on the genetic group. The multiplex PCR was evaluated by genotyping a panel of 22 unknown F. columnare isolates and performing DNA sequencing of the dnaK gene in parallel. The results demonstrated 100% accordance between multiplex PCR results and assignment to genetic group via phylogenetic analysis. The multiplex PCR provides a useful tool for assigning an unknown isolate to genetic group and may be used to determine which genetic groups of F. columnare are circulating and most predominant in different aquaculture industries.     

Comparison of Stunning Methods on the Physicochemical Properties of Frozen Nile Tilapia (Oreochromis niloticus) Fillets

This study compares how CO₂ narcosis and thermal shock affect the physicochemical aspects of Nile tilapia fillets held frozen (?18°C) for up to 6 months. The characteristics of tilapia fillets subjected to CO₂ narcosis were those of higher lightness and whiteness and lower redness. The hardness values of fillets of tilapia subjected to thermal shock were lower than those subjected to CO₂ narcosis. During frozen storage to both treatments, the drip loss, denaturation of myosin, and lipid oxidation increased, while fillet water holding capacity and hardness decreased. The physicochemical properties of frozen fillets of tilapia stunned by CO₂ narcosis were considered more desirable; therefore, the method can be a potential replacement to thermal shock.     

Effects of conjugated linoleic acid and curcumin on growth performance and oxidative stress enzymes in juvenile Pacific white shrimp (Litopenaeus vannamei) feed with aflatoxins

Aflatoxicosis is a growing problem in aquaculture. A 42‐day study was designed to evaluate the efficacy of conjugated linoleic acid (CLA) and curcumin (CUR) to protect juvenile Pacific white shrimp (Litopenaeus vannamei) from aflatoxins. Growth parameters along with alkaline phosphatase (ALP) and glutathione S‐transferase (GST) activities were measured. Shrimps (36) with an average weight of 76 ± 0.9 mg were randomly allocated in eight experimental groups. Non‐contaminated diet (NCD) and aflatoxin‐contaminated diet (ACD) at 200 μg/kg were prepared. ACD was used to prepare six diets supplemented with CLA (4, 5 or 6 g/kg) and CUR (0.15, 0.2 and 0.3 g/kg). ACD reduced feed intake, growth rate and nitrogen retention efficiency, and increased ALP and GST activity. Improved nitrogen retention was observed for all groups feed with CLA. CUR supplementation at 0.2 g/kg increased feed intake and growth rate while at 0.15 g/kg increased nitrogen retention. ALP activity was reduced in all CUR groups and in 5 and 6 g/kg CLA groups. Reduction in GST activity was observed in 0.15 and 0.2 g/kg CUR groups and 4 g/kg CLA group. CLA supplementation and CUR supplementation can be beneficial to protect juvenile shrimp against aflatoxins.     

Redox dysregulation and bioaccumulation of copper in tilapia Oreocromis niloticus

The objective of this study was to evaluate the effect of two concentrations of copper (0.13 and 0.5 mg L^?1) on juveniles of tilapia, Oreocromis niloticus (Linnaeus), using two toxicological assays (I‐ copper exposure and II‐ copper exposure followed by recovery). Doses were taken from the liver of the test organisms to determine the concentrations of copper, reduced glutathione, activities of glutathione S‐transferase and catalase, and lipid peroxidation. Exposure to copper in both assays resulted in significant accumulation of this metal in the analysed tissue and in decreased concentration of reduced glutathione. There was no alteration in the activities of catalase and glutathione S‐transferase and in lipid peroxidation.     

Seroprevalence of Neospora caninum infection in dairy and beef cattle in Paraguay

Seroprevalence of Neospora caninum in 879 beef and dairy cattle in different locations of Paraguay was determined by an ELISA. In the survey, 262 (29.8%) cattle were positive to N. caninum, and animals with anti-Neospora antibody titre were observed in all the locations tested in the country. Serum samples taken from a herd that exhibited persistent abortion had the highest percentage of animals being positive to the parasite (17/30, 56.7%). In the same herd, abortion was significantly more likely in animals with high anti-Neospora antibody titre. Immunoblot analysis demonstrated that the banding pattern from positive Paraguayan cattle was similar to that seen with the positive control sample. In conclusion, N. caninum infection is present among Paraguayan beef and dairy cattle, and it may be an important cause of bovine abortion in Paraguay.