Histological and histochemical characterisation of glands associated with the feeding appendages of Argulus foliaceus (Linnaeus, 1758)

Argulus foliaceus (Linnaeus, 1758) is a member of the branchiuran family Argulidae, a group comprising parasitic “fish lice”. A. foliaceus is distributed worldwide and causes major economic impacts for cultured freshwater fish globally. The work described in this study was undertaken with the objective of identifying, describing and characterising glands associated with feeding in A. foliaceus. From structural and ultrastructural microscopic studies of A. foliaceus, three types of gland were determined to be associated with the pre-oral spine and mouth tube and were suggested to be involved in feeding activities. Two of these glands, the labial glands and the proboscis glands, appeared to secrete their products via the mouth tube and a third, the spinal gland, was connected directly to the pre-oral spine. The current study confirmed that the pre-oral spine delivers active secretions from the spinal gland, which may aid in immunomodulation, while the tubular labial spines and proboscis glands openings within the mouth tube may serve to enhance the feeding process by delivering salivary components to aid pre-digestion and immune-modulate the host. The suggested functions are supported by histological and histochemical staining, coupled with fluorescent lectin-binding assays, which enabled characterisation of the carbohydrate moieties associated with these glandular tissues

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

Background It is hypothesised that being a blood-feeding ectoparasite, Argulus foliaceus (Linnaeus, 1758), uses similar mechanisms for digestion and host immune evasion to those used by other haematophagous ecdysozoa, including caligid copepods (e.g. sea louse). We recently described and characterised glands associated with the feeding appendages of A. foliaceus using histological techniques. The work described in the present study is the first undertaken with the objective of identifying and partially characterising the components secreted from these glands using a proteomic approach. Methods Argulus foliaceus parasites were sampled from the skin of rainbow trout (Oncorhynchus mykiss), from Loch Fad on the Isle of Bute, Scotland, UK. The proteins from A. foliaceus secretory/excretory products (SEPs) were collected from the supernatant of artificial freshwater conditioned with active adult parasites (n = 5–9 per ml; n = 560 total). Proteins within the SEPs were identified and characterised using LC-ESI-MS/MS analysis. Data are available via ProteomeXchange with identifier PXD016226. Results Data mining of a protein database translated from an A. foliaceus dataset using ProteinScape allowed identification of 27 predicted protein sequences from the A. foliaceus SEPs, each protein matching the criteria of 2 peptides with at least 4 contiguous amino acids. Nine proteins had no matching sequence through OmicsBox (Blast2GO) analysis searches suggesting that Argulus spp. may additionally have unique proteins present in their SEPs. SignalP 5.0 software, identified 13 proteins with a signal sequence suggestive of signal peptides and supportive of secreted proteins being identified. Notably, the functional characteristics of identified A. foliaceus proteins/domains have also been described from the salivary glands and saliva of other blood-feeding arthropods such as ticks. Identified proteins included: transporters, peroxidases, metalloproteases, proteases and serine protease inhibitors which are known to play roles in parasite immune evasion/induction (e.g. astacin), immunomodulation (e.g. serpin) and digestion (e.g. trypsin). Conclusions To our knowledge, the present study represents the first proteomic analysis undertaken for SEPs from any branchiuran fish louse. Here we reveal possible functional roles of A. foliaceus SEPs in digestion and immunomodulation, with a number of protein families shared with other haematophagous ectoparasites. A number of apparently unique secreted proteins were identified compared to other haematophagous ecdysozoa

Gill histology of Nile tilapia Oreochromis niloticus following chronic and acute exposure to ammonia

Ammonia is a common aquatic pollutant and is toxic to fish. The main nitrogenous compound excreted by fish is also ammonia, which may reach toxic concentrations in high-density fish culture, reducing growth and productivity. In this study, changes in gill structure and mucus cell distribution were examined when juvenile Nile tilapia, Oreochromis niloticus, were exposed to chronic and acute concentrations of ammonia. For chronic exposure, the tilapia were exposed to daily increments in ammonia concentration rising from 0 mg L-1 ammonia on Day 0 to 5 mg L-1 by Day 8; the experiment was terminated on Day 9. There were obvious histopathological changes to the gills over this period including hypertrophy and fusion and of the secondary lamellae. The mucus cell number in gill histology sections were observed to increase until Day 6 then decrease thereafter until the termination of the trial. For the acute exposure, juvenile tilapia were exposed to 5 mg L-1 ammonia for 5 hours. Hourly changes to the gills were monitored, with notable changes to gill filaments and an observed increase in the mucus cell number over the duration of the experiment.

Gill histology of Nile tilapia Oreochromis niloticus following chronic and acute exposure to ammonia

Ammonia is a common aquatic pollutant and is toxic to fish. The main nitrogenous compound excreted by fish is also ammonia, which may reach toxic concentrations in high-density fish culture, reducing growth and productivity. In this study, changes in gill structure and mucus cell distribution were examined when juvenile Nile tilapia, Oreochromis niloticus, were exposed to chronic and acute concentrations of ammonia. For chronic exposure, the tilapia were exposed to daily increments in ammonia concentration rising from 0 mg L-1 ammonia on Day 0 to 5 mg L-1 by Day 8; the experiment was terminated on Day 9. There were obvious histopathological changes to the gills over this period including hypertrophy and fusion and of the secondary lamellae. The mucus cell number in gill histology sections were observed to increase until Day 6 then decrease thereafter until the termination of the trial. For the acute exposure, juvenile tilapia were exposed to 5 mg L-1 ammonia for 5 hours. Hourly changes to the gills were monitored, with notable changes to gill filaments and an observed increase in the mucus cell number over the duration of the experiment