Brian Jones

Purpose
A previous study revealed that temnocephalids Diceratocephala boschmai, Craspedella pedum, and Decadidymus sp. were highly prevalent in Cheraq quadricarinatus in Melaka and Johor, Malaysia.

Methods
Herein, study was conducted to extract temnocephalids from C. quadricarinatus and identified using a molecular approach via two DNA markers: 28S ribosomal DNA and mitochondrial cytochrome c oxidase subunit I (CO1). Thereafter, the population diversity of D. boschmai in Malaysia using the CO1 DNA marker was analysed to visualize the genetic associations among populations.

Results
The analysis of 16 variable (segregating) sites in the CO1 gene alignment of sequence from D. boschmai revealed a calculated haplotype diversity of 0.1266 among populations which indicates genetic variation within the studied groups. Additionally, the determination of nucleotide diversity (II) yielded a value of 0.0035, and Tajima's D neutrality test yielded a negative value for all populations, suggesting no significant departure from neutral evolution.

Conclusion
AMOVA analysis indicated that the genetic variation or polymorphism is primarily contributed within populations (95%) compared to between populations (4%).

Lobsters and crayfish in Australasia can develop a condition known as Tail Fan Necrosis (TFN syndrome). Many attempts have been made to find a primary pathogen or link the syndrome to commercial activities, but a solution remains elusive. TFN syndrome is a ‘wicked problem’, a problem difficult or impossible to solve because of incomplete and contradictory information forming a matrix of potential outcomes with no simple solution. Reviewing the literature shows TFN syndrome is sometimes reported to develop in association with sterile blisters on the telson and uropods which may rupture permitting invasion by environmental fungal and/or bacterial flora. Whether blisters form prior to, or because of, infection is unknown. TFN syndrome sometimes develops in captivity, sometimes requires a previous insult to the telson and uropods, and prevalence is patchy in the wild. The literature shows the cause of blisters associated with TFN syndrome remains an enigma, for which we suggest several possible initiating factors. We strongly urge that researchers not ‘jump to conclusions’ as to the aetiology of TFN syndrome. It cannot be explained without carefully exploring alternative aetiologies whilst being cognisant of the age‐old lesson that ‘correlation does not equal causation’.

The welfare of fishes and aquatic invertebrates is important, and several jurisdictions have included these taxa under welfare regulation in recent years. Regulation of welfare requires use of scientifically validated welfare criteria. This is why applying Mertonian skepticism toward claims for sentience and pain in fishes and aquatic invertebrates is scientifically sound and prudent, particularly when those claims are used to justify legislation regulating the welfare of these taxa. Enacting welfare legislation for these taxa without strong scientific evidence is a societal and political choice that risks creating scientific and interpretational problems as well as major policy challenges, including the potential to generate significant unintended consequences. In contrast, a more rigorous science-based approach to the welfare of aquatic organisms that is based on verified, validated and measurable endpoints is more likely to result in “win-win” scenarios that minimize the risk of unintended negative impacts for all stakeholders, including fish and aquatic invertebrates. The authors identify as supporters of animal welfare, and emphasize that this issue is not about choosing between welfare and no welfare for fish and aquatic invertebrates, but rather to ensure that important decisions about their welfare are based on scientifically robust evidence. These ten reasons are delivered in the spirit of organized skepticism to orient legislators, decision makers and the scientific community, and alert them to the need to maintain a high scientific evidential bar for any operational welfare indicators used for aquatic animals, particularly those mandated by legislation. Moving forward, maintaining the highest scientific standards is vitally important, in order to protect not only aquatic animal welfare, but also global food security and the welfare of humans.

The introduction of the crayfish Cherax quadricarinatus into new areas of Malaysia resulted in the introduction of new parasites that harmed other aquatic organisms. A study was conducted to determine the prevalence and sites specificity of temnocephalids in wild and cultured Cherax quadricarinatus. In this study, 33 wild (Melaka) and 32 cultured (Johor) C. quadricarinatus were sampled in January 2020. The prevalence of the parasite was determined using dissecting microscopes and their sites specificity were compared. The prevalence (P) and mean intensity (MI) of temnocephalids in wild crayfish were 93.94% and 35.13%, whereas in the cultured crayfish were 100% and 18.31%, respectively. The temnocephalid species were identified as Diceratocephala sp., Craspedella sp., and Decadidymus sp. The prevalence of adults and eggs of Decadidymus sp. was found to be significant in cultured C. quadricarinatus (p < 0.05). Significant differences were observed by adult Diceratocephala sp. and Craspedella sp. on the cephalothorax and walking legs, and in the gills and gill covers of wild C. quadricarinatus, respectively. These findings showed that the cultured C. quadricarinatus had a higher temnocephalid infestation compared to the wild C. quadricarinatus. These different temnocephalid species occupied different niche areas, but factors accounting for their distribution on C. quadricarinatus need further investigation.

Alien crayfish, Cherax quadricarinatus (von Martens, 1868) is one of the potential cultivated freshwater species in Malaysian waters; however, its establishment in freshwater ecosystems may alter the native taxa due to the high environmental tolerance and capability of transmitting parasites. We report here the first evidence of the ectosymbiont Craspedella pedum (Cannon and Sewell, 1995) described by morphological observations and species identification using molecular techniques, originating from C. quadricarinatus collected in Malaysian freshwater. A 940-base pair long 18S ribosomal rDNA fragment, in particular, was successfully sequenced and aligned. The Neighbour-Joining and Maximum Likelihood analyses revealed a high degree of similarity with a low genetic distance between C. pedum from this study and C. pedum from Thailand. This finding represents the second discovery of temnocephalid symbionts in Malaysian waters, but first made using molecular data. This clarification may help to improve understanding of the temnocephalid infestation in Malaysia, as well as potential threats to native species and changes in ecosystem diversity where the host was introduced.

The introduction of Australian Cherax quadricarinatus into Malaysia as an aquaculture species has resulted in wild populations in several Malaysian states, and it is now considered an invasive species. The introduction coincidentally co-introduced Diceratocephalid, flatworms that externally inhabit C. quadricarinatus. Thirty-three wild C. quadricarinatus were caught alive in Tasik Ayer Keroh, Melaka; while 32 cultured C. quadricarinatus were bought in Bandar Tenggara, Johor. Two species of ecto-symbiont (Diceratocephala boschmai and Decadidymus sp.) were morphologically identified and genetically 18S rDNA sequenced. Currently, only one 18S rDNA sequence is available for Decadidymus sp. in the GenBank, isolated from redclaw crayfish, C. quadricarinatus in Australia. This D. boschmai 18S rDNA phylogenetic analysis was consistent with the data from previous studies.

Immunopathology is broadly defined as the study of immune responses associated with disease, including the study of the pathology of an organism, organ system or disease with respect to the immune system. As other chapters in this book discuss topics such as the immune responses of fish to infectious agents and the effects of stressors on the immune response, this chapter addresses a subcategory of immunopathology. Immunopathology is defined here as the study of pathological changes in organs of the immune system resulting from a variety of aetiologies, including infectious agents (viruses, bacteria, fungi and parasites) and non-infectious conditions (nutrition-related, toxicant-related and neoplasia). Whereas numerous studies on fish have focused on the host response to various stressors, relatively few have investigated immunopathology. This review utilises examples of infectious and non-infectious diseases in teleost fishes to summarise our knowledge of teleost immunopathology. For some diseases, the presence of an infectious agent or toxin may directly or indirectly cause destruction of immune organs. In other diseases, an intense inflammatory response, or conversely, suppression of the immune response, may contribute to disease progression in these organs. Other factors such as the virulence of a pathogen biotype, degree of toxicity or carcinogenicity of an exogenous element or compound, the species and age of exposed fish and environmental conditions such as water temperature and water quality can also contribute to determining the outcome of a disease. Additional research is needed to investigate the mechanisms responsible for immunopathology observed in many diseases.

This study was carried out in order to identify acanthocephalan species complexes, based on morphological variability, infecting Barbonymus schwanenfeldii from Lake Kenyir, Terengganu, Malaysia. Acanthocephala were fixed in ethanol, stained with aceto-carmine and studied morphologically by using a light microscope. Variation in morphological traits such as proboscis, proboscis receptacle, egg, testes shape and location, number of hooks and cement gland has been traditionally used to diagnose the acanthocephalans species but the delimitations between closely related species are still confusing and are always questionable among taxonomists. Molecular analysis was used for support the identification. Morphological variability prospecting reveals the presence of three different new species complexes from the subgenus Acanthosentis by referring published taxonomic keys. These new species may be distinguished from the other 46 described species of Acanthosentis by having six unique structures: the presence of an anterior parareceptacle structure (PRS); vaginal sleeve structure; a paired lateral, cone-shaped, muscular jacket surrounding the vagina; alternating pattern and size of proboscis hooks, variation in proboscis size and shape; the presence of the circular collar ring around the neck between the proboscis and trunk and lastly the presence of a muscular-like structure attached to the collar ring on the proboscis. These acanthocephalans found in the intestine of B. schwanenfeldii in Kenyir Lake Malaysia represent new species, named Acanthogyrus (Acanthosentis) kenyirensis n.sp., A. (A.) terengganuensis n.sp. and A. (A.) tembatensis n. sp.

Bonamia ostreae is a haplosporidian parasite of oysters that was first reported to occur in the Southern Hemisphere in 2015 in the New Zealand flat oyster Ostrea chilensis. Until that report, B. ostreae had been restricted to populations of O. edulis within the Northern Hemisphere. This large range extension raised questions regarding B. ostreae dispersal, including whether B. ostreae is a recent introduction and from where it originated. The whole 18S rRNA gene of New Zealand B. ostreae revealed 99.9-100% sequence homology to other published B. ostreae 18S rDNA sequences. Internal transcribed spacer (ITS) rDNA sequences (n = 29) were generated from New Zealand B. ostreae and compared to published B. ostreae sequences from 3 Northern Hemisphere sites: California, USA (n = 18), Maine, USA (n = 7), and the Netherlands (n = 6) to investigate intraspecific variation. Low ITS rDNA variation was observed from New Zealand B. ostreae isolates, and high levels of variation were observed from Northern Hemisphere B. ostreae sequences. We hypothesise that the low ITS rDNA diversity found in New Zealand B. ostreae is the result of a founder effect resulting from a single introduction from a limited number of propagules. The high level of ITS rDNA variation from the Northern Hemisphere prevented inferences of dispersal origins. New Zealand B. ostreae were genetically differentiated from all sites, and additional genetic data are required to better determine the origin of B. ostreae in New Zealand.

The endemic green-lipped mussel (GLM) Perna canaliculus is a key cultural and economic species for New Zealand. Unlike other cultured shellfish species, GLMs have experienced relatively few disease issues. The apparent absence of diseases in both wild and farmed GLM populations does not preclude risks from environmental changes or from the introduction of overseas mussel pathogens and parasites. Potential for disease exchange between the GLM and other mytilid species present in New Zealand has yet to be elucidated. After reviewing and discussing relevant scientific literature, we present an initial assessment of GLM vulnerability to disease threats and the potential risk pathways for mussel pathogens and parasites into New Zealand and highlight a number of challenges. These include knowledge gaps relevant to GLM susceptibility to exotic pathogens and parasites, risk pathways into New Zealand and biosecurity risk associated with domestic pathways. Considerations and findings could potentially apply to other farmed aquatic species with limited distribution range and/or low disease exposure.