Three-dimensional visualisation of developmental stages of an apicomplexan fish blood parasite in its invertebrate host

Access to Cleaning Services Alters Fish Physiology Under Parasite Infection and Ocean Acidification

Cleaning symbioses are key mutualistic interactions where cleaners remove ectoparasites and tissues from client fishes. Such interactions elicit beneficial effects on clients’ ecophysiology, with cascading effects on fish diversity and abundance. Ocean acidification (OA), resulting from increasing CO₂ concentrations, can affect the behavior of cleaner fishes making them less motivated to inspect their clients. This is especially important as gnathiid fish ectoparasites are tolerant to ocean acidification. Here, we investigated how access to cleaning services, performed by the cleaner wrasse Labroides dimidiatus, affect individual client’s (damselfish, Pomacentrus amboinensis) aerobic metabolism in response to both experimental parasite infection and OA. Access to cleaning services was modulated using a long-term removal experiment where cleaner wrasses were consistently removed from patch reefs around Lizard Island (Australia) for 17 years or left undisturbed. Only damselfish with access to cleaning stations had a negative metabolic response to parasite infection (maximum metabolic rate—ṀO_2Max; and both factorial and absolute aerobic scope). Moreover, after an acclimation period of 10 days to high CO₂ (∼1,000 µatm CO₂), the fish showed a decrease in factorial aerobic scope, being the lowest in fish without the access to cleaners. We propose that stronger positive selection for parasite tolerance might be present in reef fishes without the access to cleaners, but this might come at a cost, as readiness to deal with parasites can impact their response to other stressors, such as OA.

Molecular insights into the identification and phylogenetics of the cosmopolitan marine fish blood parasite, Haemogregarina bigemina (Adeleorina: Haemogregarinidae)

Haemogregarina bigemina is one of the most prevalent haemogregarines of marine fishes and has long been considered an enigmatic and cosmopolitan species. However, to determine whether H. bigemina truly represents a single global species, or whether it should be partitioned into several species or subspecies, and to confirm its taxonomic status among the Haemogregarina, molecular analysis is required. Here, we provide the first molecular characterisation of H. bigemina from one of its type hosts, Lipophrys pholis, in the UK using 18S rDNA sequences. Phylogenetic and p-distance comparisons of the newly generated H. bigemina sequences with those published from other haemogregarine taxa and related apicomplexans suggest that H. bigemina falls outside of the "Haemogregarina" clade as well as the Adeleorina altogether, forming a separate apicomplexan marine clade, and appears to be in fact more closely related to other non-haemogregarine Apicomplexa genera. Further work including sequences of H. bigemina and H. bigemina-like parasites observed from fishes in other localities is now needed to investigate this further.

Morphological and molecular characterization of a marine fish trypanosome from South Africa, including its development in a leech vector

Background

Trypanosomes are ubiquitous blood parasites of marine and freshwater fishes, typically transmitted by aquatic leeches. Phylogenetic studies have been dominated by examples derived from freshwater fishes, with few marine representatives. Furthermore, life cycle studies on marine fish trypanosomes have focused on those of the northern hemisphere. In this investigation, we have examined the life cycle and molecular taxonomy of a marine fish trypanosome from South Africa.

Methods

To locate trypanosome stages, leeches were removed from fishes captured on the west and south coasts of South Africa, and fish blood films and leech squashes were Giemsa-stained and screened; leeches were also examined histologically. To determine whether trypanosome stages in fishes and leeches were of the same genotype, DNA was extracted from Giemsa-stained fish blood films and leech squashes, and from fish whole blood. Fragments of the 18S rRNA gene were amplified by PCR using trypanosome-specific primers and sequenced. Resulting sequence data were compared with each other and with published trypanosome 18S rDNA sequences, and used for phylogenetic analysis.

Results

Trypanosomes were detected in blood films from fishes of the families Clinidae, Blenniidae and Gobiidae. The flagellates ranged in size and staining properties within the films and across fish hosts. In squashes and histological sections of adult and juvenile leeches, identified as Zeylanicobdella arugamensis, trypanosome developmental stages were predominantly slender epimastigotes. Sequence data showed that trypanosomes derived from fishes were identical, irrespective of whether they were small or large forms; sequences derived largely from leech epimastigotes were also identical to those obtained from fish trypanosomes. Fish and leech trypanosome sequences fell into a marine fish aquatic clade, and aligned most closely with two trypanosome sequences from marine fishes off Norway.

Conclusions

Combined morphological and molecular methods indicate that the trypanosomes examined here represent a single pleomorphic species, rather than the three species described originally. This species is identified as Trypanosoma nudigobii Fantham, 1919 with the leech Z. arugamensis as its vector, and T. capigobii Fantham, 1919 and T. blenniclini Fantham, 1930 are regarded as junior synonyms of the species. Phylogenetic analysis establishes its affinity with marine fish trypanosomes off Norway.