Host impact of monogenean Lepidotrema bidyana infection and intensity estimates for onsite monitoring

Fish ectoparasite detection, collection and curation

Fish parasitology is a dynamic and internationally important discipline with numerous biological, ecological and practical applications. We reviewed optimal fish and parasite sampling methods for key ectoparasite phyla (i.e. Ciliophora, Platyhelminthes, Annelida and Arthropoda) as well as recent advances in molecular detection of ectoparasites in aquatic environments. Ideally, fish capture and anaesthesia as well as parasite recovery methods should be validated to eliminate potential sampling bias and inaccuracy in determining ectoparasite population parameters. There are considerable advantages to working with fresh samples and live parasites, when combined with appropriate fixation methods, as sampling using dead or decaying materials can lead to rapid decomposition of soft-bodied parasites and subsequent challenges for identification. Sampling methods differ between target phyla, and sometimes genera, with optimum techniques largely associated with identification of parasite microhabitat and the method of attachment. International advances in fish parasitology can be achieved through the accession of whole specimens and/or molecular voucher specimens (i.e. hologenophores) in curated collections for further study. This approach is now critical for data quality because of the increased application of environmental DNA (eDNA) for the detection and surveillance of parasites in aquatic environments where the whole organism may be unavailable. Optimal fish parasite sampling methods are emphasised to aid repeatability and reliability of parasitological studies that require accurate biodiversity and impact assessments, as well as precise surveillance and diagnostics.

Comparison of bacterial diversity and distribution on the gills of Atlantic salmon (Salmo salar L.): an evaluation of sampling techniques

AIMS

Assess bacterial diversity and richness in mucus samples from the gills of Atlantic salmon in comparison to preserved or fixed gill filament tissues. Ascertain whether bacterial diversity and richness are homogeneous upon different arches of the gill basket.

METHODS AND RESULTS

Bacterial communities contained within gill mucus were profiled using 16S rRNA gene sequencing. No significant difference in taxa richness, alpha (P > 0·05) or beta diversity indices (P > 0·05) were found between the bacterial communities of RNAlater preserved gill tissues and swab-bound mucus. A trend of lower richness and diversity indices were observed in bacterial communities from posterior hemibranchs.

CONCLUSIONS

Non-lethal swab sampling of gill mucus provides a robust representation of bacterial communities externally upon the gills. Bacterial communities from the fourth arch appeared to be the least representative overall.

SIGNIFICANCE AND IMPACT OF THE STUDY

The external mucosal barriers of teleost fish (e.g. gill surface) play a vital role as a primary defence line against infection. While research effort on the role of microbial communities on health and immunity of aquaculture species continues, the collection and sampling processes to obtain these data require evaluation so methodologies are consistently applied across future studies that aim to evaluate the composition of branchial microbiomes.

Chronic effects of a monogenean Ligictaluridus floridanus (Ancyrocephalidae) infection on channel catfish (Ictalurus punctatus) growth performance

In aquaculture, acute infections may result in fish mortality, but in many cases the chronic effects of infections are not readily detected, and may result in a decrease in fish growth. Ligictaluridus floridanus is a gill monogenean parasite prevalent on channel catfish (Ictalurus punctatus) farms in Northeastern Mexico. In order to assess and evaluate the impact of the chronic infection with this monogenean, 400 six-month-old catfish fingerlings from a hatchery, with a fork length of 10–15 cm were used in this study. Catfish naturally infected with L. floridanus (parasite abundance was 18) were divided in two groups of 200 fish. One group was treated with formalin, and infection was eliminated during a week, while the other group was not treated, and was used as a control. In total, 111 fish of each group were selected, placed into aquaria, and observed for 12 weeks. Indicators of growth such as fork length, mean weight, condition index, specific growth rate, feed conversion index and feed consumed were assessed. Significant differences (P < 0.05) between the treated group and control were found in the mean weight (127.85 g and 107.63 g) and specific growth rate (1.79 and 1.58), respectively. No significant differences were found in the other growth indicators assessed. We proved that growth performance of channel catfish is affected by infection with L. floridanus, which influence the farm economy. This is the first report on the effect of L. floridanus on the growth performance of channel catfish.

Efficacy of bath and orally administered praziquantel and fenbendazole against Lepidotrema bidyana Murray, a monogenean parasite of silver perch, Bidyanus bidyanus (Mitchell)

We investigated the efficacy of praziquantel (PZQ) and fenbendazole (FBZ), each administered by bath and orally, against the monogenean Lepidotrema bidyana Murray, a gill parasite of the freshwater fish silver perch, Bidyanus bidyanus (Mitchell). PZQ and FBZ were each administered by bath at 10 mg L⁻¹ for 48 h and on surface-coated feed pellets at 75 mg kg⁻¹ per body weight (BW) per day for 6 days. Bath treatments of PZQ and FBZ had an efficacy of 99% and 91%, respectively, against adult L. bidyana. Oral treatments of PZQ and FBZ had an efficacy of 79% and 95%, respectively, against adult L. bidyana. Fish rejected feed pellets surface-coated with PZQ, suggesting that palatability of surface-coated PZQ-medicated feed is poor, which undermined efficacy. In all trials, some juvenile parasites were present on fish after treatment during efficacy assessment, indicating that efficacy may be lower against juvenile parasites or that recruitment occurred post-treatment, demonstrating that repeat treatments are necessary to effectively control L. bidyana in aquaculture.

Validation of a rapid counting method for assessing treatment efficacy against Lepidotrema bidyana infecting silver perch Bidyanus bidyanus

We used a published sub-sampling method for estimating the abundance of the monogenean Lepidotrema bidyana, a gill parasite of silver perch Bidyanus bidyanus, and determined that it also accurately predicts parasite abundance post-treatment. Post-treatment parasite abundance estimates based on the number of parasites on the first left posterior hemibranch were compared to actual counts on fish after bath and oral treatment trials with praziquantel and fenbendazole. Post-treatment parasite abundance estimates were significantly correlated to real counts of all individual hemibranchs, accurately predicting the parasite abundance on an individual host. There was no significant difference in the post-treatment parasite abundance between individual hemibranchs, however, indicating that the treatment affected L. bidyana abundance on each hemibranch unequally. Use of this method is ineffective at predicting post-treatment abundance; however, it accurately predicts the remaining parasite abundance, aiding evaluation of treatment efficacy, while reducing post-treatment sampling time or facilitating larger sample sizes.