Transcriptional analysis of immune-relevant genes in the mucus of Labeo rohita, experimentally infected with Argulus siamensis

Fish Skin Mucus Extracts: An Underexplored Source of Antimicrobial Agents

The slow discovery of new antibiotics combined with the alarming emergence of antibiotic-resistant bacteria underscores the need for alternative treatments. In this regard, fish skin mucus has been demonstrated to contain a diverse array of bioactive molecules with antimicrobial properties, including peptides, proteins, and other metabolites. This review aims to provide an overview of the antimicrobial molecules found in fish skin mucus and its reported in vitro antimicrobial capacity against bacteria, fungi, and viruses. Additionally, the different methods of mucus extraction, which can be grouped as aqueous, organic, and acidic extractions, are presented. Finally, omic techniques (genomics, transcriptomics, proteomics, metabolomics, and multiomics) are described as key tools for the identification and isolation of new antimicrobial compounds. Overall, this study provides valuable insight into the potential of fish skin mucus as a promising source for the discovery of new antimicrobial agents.

Stability evaluation and validation of appropriate reference genes for real-time PCR expression analysis of immune genes in the rohu (Labeo rohita) skin following argulosis

Argulosis is one of the most unrestrained economically significant freshwater fish ectoparasitic diseases. Proper selection or normalization of the best reference gene governs the accuracy of results of gene expression studies using real-time PCR. Earlier studies in rohu carp (Labeo rohita) have used reference genes without proper validation. Here, seven candidate reference genes viz., acidic ribosomal protein (ARP0), glyceraldehyde 3-phosphate dehydrogenase, RNA polymerase II (RPo), elongation factor1α (EF1α), α- tubulin (AT), ribosomal protein L 10, and β-actin were evaluated using four algorithms (geNorm, BestKeeper, NormFinder and ∆Ct) followed by a comprehensive gene expression analysis using skin tissue of rohu at varied time points of experimental Argulus siamensis infection. ARP0 and EF1α were found to be the most stable whereas RPo and AT were considered as least stable genes based on basal expression level and variation in expression levels. Validation of candidate reference genes was undertaken by looking into the expression of six immune-related genes using the two most stable and two least stable genes as housekeeping genes in Argulus-infected rohu skin at different time points of infection. An increased expression of immune genes indicated the role of inflammation and the immune modulation process at the site of attachment of parasites in governing infection.

An insight into the interaction between Argulus siamensis and Labeo rohita offers future therapeutic strategy to combat argulosis

Aquaculture and fisheries are salient flourishing sectors in the world but their sustainability is often afflicted by several pathogenic diseases. Among all the pathogenic diseases of fish, parasitic diseases are found to be a major cause of concern. Argulosis is one of the dominant parasitic problems encountered in Indian aquaculture practices. Argulus siamensis is the most prevalent argulid species harming the Indian major carp species including Labeo rohita. The major carps respond to parasitic infestation by elevating various immune relevant genes. The therapeutic chemicals, synthetic drugs and other plant extracts have made a progress in the fight against argulosis. However, there is no effective vaccine and drugs are available for this disease. Thus, designing efficient, cost-effective and eco-friendly control and treatment strategies for argulosis is presently needed. Keeping the aforementioned facts in mind, the current review elaborated the immunological interaction between A. siamensis and L. rohita, available combat tactics, highlighted the already identified vaccine candidates to design effective control measures and illustrated the use of omics technology in future to combat argulosis.

Cleaner fish are potential super-spreaders

Cleaning symbiosis is critical for maintaining healthy biological communities in tropical marine ecosystems. However, potential negative impacts of mutualism, such as the transmission of pathogens and parasites during cleaning interactions, have rarely been evaluated. Here, we investigated whether the dedicated bluestreak cleaner wrasse Labroides dimidiatus, is susceptible to, and can transmit generalist ectoparasites between client fish. In laboratory experiments, L. dimidiatus were exposed to infective stages of three generalist ectoparasite species with contrasting life-histories. Labroides dimidiatus were susceptible to infection by the gnathiid isopod, Gnathia aureamaculosa, but significantly less susceptible to the ciliate protozoan, Cryptocaryon irritans, and the monogenean flatworm, Neobenedenia girellae, compared to control host species (Coris batuensis or Lates calcarifer). The potential for parasite transmission from a client fish to the cleaner fish was simulated using experimentally transplanted mobile adult (i.e., egg-producing) monogenean flatworms on L. dimidiatus. Parasites remained attached to cleaners for an average of two days, during which parasite egg production continued, but was reduced compared to control fish. Over this timespan, a wild cleaner may engage in several thousand cleaning interactions, providing numerous opportunities for mobile parasites to exploit cleaners as vectors. Our study provides the first experimental evidence that L. dimidiatus exhibits resistance to infective stages of some parasites yet has the potential to temporarily transport adult parasites. We propose that some parasites that evade being eaten by cleaner fish could exploit cleaning interactions as a mechanism for transmission and spread.

Review on Immersion Vaccines for Fish: An Update 2019

Immersion vaccines are used for a variety of aquacultured fish to protect against infectious diseases caused by bacteria and viruses. During immersion vaccination the antigens are taken up by the skin, gills or gut and processed by the immune system, where the resulting response may lead to protection. The lack of classical secondary responses following repeated immersion vaccination may partly be explained by the limited uptake of antigens by immersion compared to injection. Administration of vaccines depends on the size of the fish. In most cases, immersion vaccination is inferior to injection vaccination with regard to achieved protection. However, injection is problematic in small fish, and fry as small as 0.5 gram may be immersion vaccinated when they are considered adaptively immunocompetent. Inactivated vaccines are, in many cases, weakly immunogenic, resulting in low protection after immersion vaccination. Therefore, during recent years, several studies have focused on different ways to augment the efficacy of these vaccines. Examples are booster vaccination, administration of immunostimulants/adjuvants, pretreatment with low frequency ultrasound, use of live attenuated and DNA vaccines, preincubation in hyperosmotic solutions, percutaneous application of a multiple puncture instrument and application of more suitable inactivation chemicals. Electrostatic coating with positively charged chitosan to obtain mucoadhesive vaccines and a more efficient delivery of inactivated vaccines has also been successful.