Marine Herbivorous Fish Research Articles

Diet Shifts Alter the Activity and Distribution of Digestive Enzymes in an Herbivorous Fish

The digestive tract is central to the function of an animal since it assimilates nutrients from the diet. Digestion itself is a chemical process and digestive enzymes are the digestive catalysts. Thus, we measured amylase, maltase, N-acetyl-b-d-glucosaminidase, lipase, trypsin, aminopeptidase, and alkaline phosphatase activities along the digestive tract of the marine herbivorous fish, Cebidichthys violaceus. We did this for wild-caught individuals of this species, and compared those to individuals fed carnivore, omnivore, and herbivore diets in the laboratory for six months. In laboratory fish, the enzymatic activities were generally lower compared to wild-caught fish. In wild caught fish, a strong anterior-to-posterior gradient of amylase activity was observed along the gut and this pattern largely disappeared in the lab-fed fish. N-acetyl-β-D-glucosaminidase (NAGase), which breaks down chitin products, showed an increase in activity in the distal intestines of the lab-fed fish, which is not observed in wild fish. The NAGase activity of the herbivorous fishes correlate with the bacterial species Paroccus sp., which is a known NAGase producer, and one of the dominant microbes in the distal intestines of the lab-fed fish. The role of this enzyme, however, remains unclear since the lab diets did not contain large amounts of chitin. These enzymatic differences tell us how much fish can modify their enzymatic activity to align with their diet. In summary, the findings show that C. violaceous can endure different degrees of protein and carbohydrate levels, within limits. Their digestive system clearly changed in response to more protein in the diet, along with a microbiome that had more potential pathogens. Live algal diets would may be the most suitable for this herbivorous fish based on the totality of gathered data from the lab. American Physiological Society Fellowship UCI Microbiome Initiative Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Bacteroidia and Clostridia are equipped to degrade a cascade of polysaccharides along the hindgut of the herbivorous fish Kyphosus sydneyanus.

The gut microbiota of the marine herbivorous fish Kyphosus sydneyanus are thought to play an important role in host nutrition by supplying short-chain fatty acids (SCFAs) through fermentation of dietary red and brown macroalgae. Here, using 645 metagenome-assembled genomes (MAGs) from wild fish, we determined the capacity of different bacterial taxa to degrade seaweed carbohydrates along the gut. Most bacteria (99%) were unclassified at the species level. Gut communities and CAZyme-related transcriptional activity were dominated by Bacteroidia and Clostridia. Both classes possess genes CAZymes acting on internal polysaccharide bonds, suggesting their role initiating glycan depolymerization, followed by rarer Gammaproteobacteria and Verrucomicrobiae. Results indicate that Bacteroidia utilize substrates in both brown and red algae, whereas other taxa, namely, Clostridia, Bacilli, and Verrucomicrobiae, utilize mainly brown algae. Bacteroidia had the highest CAZyme gene densities overall, and Alistipes were especially enriched in CAZyme gene clusters (n = 73 versus just 62 distributed across all other taxa), pointing to an enhanced capacity for macroalgal polysaccharide utilization (e.g., alginate, laminarin, and sulfated polysaccharides). Pairwise correlations of MAG relative abundances and encoded CAZyme compositions provide evidence of potential inter-species collaborations. Co-abundant MAGs exhibited complementary degradative capacities for specific substrates, and flexibility in their capacity to source carbon (e.g., glucose- or galactose-rich glycans), possibly facilitating coexistence via niche partitioning. Results indicate the potential for collaborative microbial carbohydrate metabolism in the K. sydneyanus gut, that a greater variety of taxa contribute to the breakdown of brown versus red dietary algae, and that Bacteroidia encompass specialized macroalgae degraders.

Chakrabartyella piscis gen. nov., sp. nov., a member of the family Lachnospiraceae, isolated from the hindgut of the marine herbivorous fish Kyphosus sydneyanus.

A Gram-stain-negative, non-spore-forming, rod-shaped, obligately anaerobic bacterium, designated strain BP5GT, was isolated from the hindgut of a silver drummer (Kyphosus sydneyanus) fish collected from the Hauraki Gulf, New Zealand. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the isolate belonged to the family Lachnospiraceae in the phylum Bacillota and was most closely related to Anaerotignum propionicum with 94.06 % sequence identity. Isolate BP5GT grew on agar medium containing mannitol and fish gut fluid as carbon sources. Clear colonies of approximately 1 mm diameter of the isolate grew within a week at 20-28 °C (optimum, 28 °C) and pH 7.6-8.5 (optimum, pH 8.5). Strain BP5GT was very sensitive to NaCl and the optimal concentration for growth was 0.045 % (w/v). Acetate and propionate were the major fermentation products. The major cellular fatty acids were C12 : 0, C14 : 0, C15 : 0 and C16 : 0. The genome sequence of the isolate was determined. Its G+C content was 38.41 mol% and the 71.41 % average nucleotide identity of the BP5GT genome to its closest neighbour with a sequenced genome (A. propionicum DSM 1682T) indicated low genomic relatedness. Based on the phenotypic and taxonomic characteristics observed in this study, a novel genus and species named Chakrabartyella piscis gen. nov., sp. nov. is proposed for isolate BP5GT (=ICMP 24687T=JCM 35769T).

Host individual and gut location are more important in gut microbiota community composition than temporal variation in the marine herbivorous fish Kyphosus sydneyanus

BackgroundGut microbiota play a key role in the nutrition of many marine herbivorous fishes through hindgut fermentation of seaweed. Gut microbiota composition in the herbivorous fish Kyphosus sydneyanus (family Kyphosidae) varies between individuals and gut sections, raising two questions: (i) is community composition stable over time, especially given seasonal shifts in storage metabolites of dietary brown algae, and (ii) what processes influence community assembly in the hindgut?ResultsWe examined variation in community composition in gut lumen and mucosa samples from three hindgut sections of K. sydneyanus collected at various time points in 2020 and 2021 from reefs near Great Barrier Island, New Zealand. 16S rRNA gene analysis was used to characterize microbial community composition, diversity and estimated density. Differences in community composition between gut sections remained relatively stable over time, with little evidence of temporal variation. Clostridia dominated the proximal hindgut sections and Bacteroidia the most distal section. Differences were detected in microbial composition between lumen and mucosa, especially at genus level.ConclusionsHigh variation in community composition and estimated bacterial density among individual fish combined with low variation in community composition temporally suggests that initial community assembly involved environmental selection and random sampling/neutral effects. Community stability following colonisation could also be influenced by historical contingency, where early colonizing members of the community may have a selective advantage. The impact of temporal changes in the algae may be limited by the dynamics of substrate depletion along the gut following feeding, i.e. the depletion of storage metabolites in the proximal hindgut. Estimated bacterial density, showed that Bacteroidota has the highest density (copies/mL) in distal-most lumen section V, where SCFA concentrations are highest. Bacteroidota genera Alistipes and Rikenella may play important roles in the breakdown of seaweed into useful compounds for the fish host.

Herbivorous Fish Microbiome Adaptations to Sulfated Dietary Polysaccharides.

Marine herbivorous fish that feed primarily on macroalgae, such as those from the genus Kyphosus, are essential for maintaining coral health and abundance on tropical reefs. Here, deep metagenomic sequencing and assembly of gut compartment-specific samples from three sympatric, macroalgivorous Hawaiian kyphosid species have been used to connect host gut microbial taxa with predicted protein functional capacities likely to contribute to efficient macroalgal digestion. Bacterial community compositions, algal dietary sources, and predicted enzyme functionalities were analyzed in parallel for 16 metagenomes spanning the mid- and hindgut digestive regions of wild-caught fishes. Gene colocalization patterns of expanded carbohydrate (CAZy) and sulfatase (SulfAtlas) digestive enzyme families on assembled contigs were used to identify likely polysaccharide utilization locus associations and to visualize potential cooperative networks of extracellularly exported proteins targeting complex sulfated polysaccharides. These insights into the gut microbiota of herbivorous marine fish and their functional capabilities improve our understanding of the enzymes and microorganisms involved in digesting complex macroalgal sulfated polysaccharides. IMPORTANCE This work connects specific uncultured bacterial taxa with distinct polysaccharide digestion capabilities lacking in their marine vertebrate hosts, providing fresh insights into poorly understood processes for deconstructing complex sulfated polysaccharides and potential evolutionary mechanisms for microbial acquisition of expanded macroalgal utilization gene functions. Several thousand new marine-specific candidate enzyme sequences for polysaccharide utilization have been identified. These data provide foundational resources for future investigations into suppression of coral reef macroalgal overgrowth, fish host physiology, the use of macroalgal feedstocks in terrestrial and aquaculture animal feeds, and the bioconversion of macroalgae biomass into value-added commercial fuel and chemical products.

Dietary-induced changes in the hindgut microbiome and metabolism of a marine herbivorous fish

To advance our understanding of the factors that influence gut physiology and function, we are examining how the gut microbiome changes under varying environments and diets. We integrated the gut transcriptome and microbiome to understand how dietary changes impact Cebidichthys violaceus, an herbivorous fish native to the California coast that is known to have an active microbial community in its hindgut. Wild-caught fish from San Simeon, California were fed either herbivore, omnivore, or carnivore diets in the laboratory for six months. We expected the microbiome, as well as the hindgut and liver transcriptome, to change with dietary perturbations, with wild herbivorous fish being most similar to lab-herbivore fish. Wild fish microbial communities were indeed different from laboratory-fed fish (P<0.001, Bray-Curtis distances), but the laboratory-omnivore diet fish were the most similar to wild fish, sharing a high abundance of taxa in the Bacteroidota and Bacillota (Families Ruminococcaceae and Rikenellaceae), whereas the laboratory-herbivore and laboratory-carnivore fish shared a high abundance of taxa from the Pseudomonodota (Families Burkholderiaceae and Oxalobacteraceae). The microbial diversity patterns in multivariate space among the fish on the different diets directly resembled that of host distal intestine gene expression in multivariate space (i.e., wild and lab-omnivore diet fish were the most similar). The hindgut had 519 differentially expressed genes, and wild fish highly express genes involved in ion transport and lipid and glucose metabolism. The liver, on the other hand, presented 4650 differentially expressed genes, and wild fish highly express genes for fatty acid synthesis and proteolysis. These data show how the gut microbiome and transcriptome varies as a function of different diets in an herbivorous marine fish. Our project provides insight into what it takes for fish to deal with shifting resources, which is important for marine resource management and new potential aquaculture species development. NSF Grant IOS-1355224 and William Townsend Porter Pre-doctoral Fellowship from the American Physiological Society. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sources of variation in community composition of the hindgut microbiota in two tropical Kyphosus species

Gut microbiota play a fundamental role in the nutrition of many vertebrate herbivores through foregut and hindgut fermentation of plant carbohydrates. Some species of marine herbivorous fishes contain moderate to high levels of short-chain fatty acids in the hindgut, indicating the importance of hindgut fermentation. Herbivorous fish hindgut microbiota are diverse and can vary with geographic location, but data on the scale of geographic variation involving a few km of separation are limited. Here, we used the 16S rRNA gene to describe community composition of the gut microbiota of the herbivorous species Kyphosus vaigiensis and K. cinerascens collected in the vicinity of Lizard Island, northern Great Barrier Reef, Australia, in 2011 and 2017. Microbiota community structure differed between posterior hindgut sections, host species, sampling years and two mid-shelf and outer reef locations approximately 20 km apart. Hindgut bacterial community composition varied remarkably between mid-shelf and outer reef locations, and among individual fish on the mid-shelf reef. In both fish species, the most abundant phyla were Pseudomonadota, Bacillota and Bacteroidota, followed by Spirochaetota, Thermodesulfobacteriota and Verrucomicrobiota. There were no clear differences between the host species in terms of the relative abundance and composition of bacterial genera in outer reef samples. In contrast, the dominant genera differed between mid-shelf samples of K. cinerascens and K. vaigiensis, being Endozoicomonas-like (Pseudomonadota) and Brevinema (Spirochaetota), respectively. Endozoicomonas are emerging as important symbionts in many marine hosts worldwide and are thought to be important in the coral sulphur cycle. Differences in microbiota composition were not associated with variation in fish condition, suggesting that the different microbial taxa perform equivalent functional roles.

Shift and homogenization of gut microbiome during invasion in marine fishes

Biological invasion is one of the main components of global changes in aquatic ecosystems. Unraveling how establishment in novel environments affects key biological features of animals is a key step towards understanding invasion. Gut microbiome of herbivorous animals is important for host health but has been scarcely assessed in invasive species. Here, we characterized the gut microbiome of two invasive marine herbivorous fishes (Siganus rivulatus and Siganus luridus) in their native (Red Sea) and invaded (Mediterranean Sea) ranges. The taxonomic and phylogenetic diversity of the microbiome increased as the fishes move away from the native range and its structure became increasingly different from the native microbiome. These shifts resulted in homogenization of the microbiome in the invaded range, within and between the two species. The shift in microbial diversity was associated with changes in its functions related with the metabolism of short-chain fatty acids. Altogether, our results suggest that the environmental conditions encountered by Siganidae during their expansion in Mediterranean ecosystems strongly modifies the composition of their gut microbiome along with its putative functions. Further studies should pursue to identify the precise determinants of these modifications (e.g. changes in host diet or behavior, genetic differentiation) and whether they participate in the ecological success of these species.

Tannockella kyphosi gen. nov., sp. nov., a member of the family Erysipelotrichaceae, isolated from the hindgut of the marine herbivorous fish Kyphosus sydneyanus.

A Gram-stain-positive, non-spore-forming, rod-shaped, obligately anaerobic bacterium, designated strain BP52GT, was isolated from the hindgut of a Silver Drummer (Kyphosus sydneyanus) fish collected from the Hauraki Gulf, New Zealand. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that the isolate belonged to the family Erysipelotrichaceae in the phylum Firmicutes and was most closely related to Clostridium saccharogumia with 93.3 % sequence identity. Isolate BP52GT grew on agar medium containing mannitol as the sole carbon source. White, opaque and shiny colonies of the isolate measuring approximately 1 mm diameter grew within a week at 20-28 °C (optimum, 24 °C) and pH 6.9-8.5 (optimum, pH 7.8). BP52GT tolerated the addition of up to 1 % NaCl to the medium. Formate and acetate were the major fermentation products. The major cellular fatty acids were C16 : 0, C16:1n-7t and C18:1n-7t. The genome sequence of the isolate was determined. Its G+C content was 30.7 mol%, and the 72.65 % average nucleotide identity of the BP52GT genome to its closest neighbour with a completely sequenced genome (Erysipelatoclostridium ramosum JCM 1298T) indicated low genomic relatedness. Based on the phenotypic and taxonomic characteristics observed in this study, a novel genus and species Tannockella kyphosi gen. nov., sp. nov. is proposed for isolate BP52GT (=NZRM 4757T=JCM 34692T).

Fine scale transitions of the microbiota and metabolome along the gastrointestinal tract of herbivorous fishes

BackgroundGut microorganisms aid in the digestion of food by providing exogenous metabolic pathways to break down organic compounds. An integration of longitudinal microbial and chemical data is necessary to illuminate how gut microorganisms supplement the energetic and nutritional requirements of animals. Although mammalian gut systems are well-studied in this capacity, the role of microbes in the breakdown and utilization of recalcitrant marine macroalgae in herbivorous fish is relatively understudied and an emerging priority for bioproduct extraction. Here we use a comprehensive survey of the marine herbivorous fish gut microbial ecosystem via parallel 16S rRNA gene amplicon profiling (microbiota) and untargeted tandem mass spectrometry (metabolomes) to demonstrate consistent transitions among 8 gut subsections across five fish of the genus of Kyphosus.ResultsIntegration of microbial phylogenetic and chemical diversity data reveals that microbial communities and metabolomes covaried and differentiated continuously from stomach to hindgut, with the midgut containing multiple distinct and previously uncharacterized microenvironments and a distinct hindgut community dominated by obligate anaerobes. This differentiation was driven primarily by anaerobic gut endosymbionts of the classes Bacteroidia and Clostridia changing in concert with bile acids, small peptides, and phospholipids: bile acid deconjugation associated with early midgut microbiota, small peptide production associated with midgut microbiota, and phospholipid production associated with hindgut microbiota.ConclusionsThe combination of microbial and untargeted metabolomic data at high spatial resolution provides a new view of the diverse fish gut microenvironment and serves as a foundation to understand functional partitioning of microbial activities that contribute to the digestion of complex macroalgae in herbivorous marine fish.

Distinct microbiota composition and fermentation products indicate functional compartmentalization in the hindgut of a marine herbivorous fish.

Many marine herbivorous fishes harbour diverse microbial communities in the hindgut that can play important roles in host health and nutrition. Kyphosus sydneyanus is a temperate marine herbivorous fish that feeds predominantly on brown seaweeds. We employed 16S rRNA gene amplicon sequencing and gas chromatography to characterize microbial communities and their metabolites in different hindgut regions of six K. sydneyanus. Measurements were confined to three distal sections of the intestine, labelled III, IV and V from anterior to posterior. A total of 625 operational taxonomic units from 20 phyla and 123 genera were obtained. Bacteroidota, Firmicutes and Proteobacteria were the major phyla in mean relative abundance, which varied along the gut. Firmicutes (76%) was the most dominant group in section III, whereas Bacteroidota (69.3%) dominated section V. Total short‐chain fatty acid (SCFA) concentration was highest in sections IV and V, confirming active fermentation in these two most distal sections. The abundance of Bacteroidota correlated with propionate concentration in section V, while Firmicutes positively correlated with formate in sections III and IV. Acetate levels were highest in sections IV and V, which correlated with abundance of Bacteroidota. Despite differences in gut microbial community composition, SCFA profiles were consistent between individual fish in the different hindgut regions of K. sydneyanus, although proportions of SCFAs differed among gut sections. These findings demonstrate functional compartmentalization of the hindgut microbial community, highlighting the need for regional sampling when interpreting overall microbiome function. These results support previous work suggesting that hindgut microbiota in marine herbivorous fish are important to nutrition in some host species by converting dietary carbohydrates into metabolically useful SCFAs.

Histology and ultrastructure of the gastrointestinal tract in four temperate marine herbivorous fishes.

While alimentary tract anatomy in many terrestrial herbivorous vertebrates is well documented, the digestive systems of marine herbivorous fishes are poorly characterised. The gastrointestinal tract (GIT) of four species of marine herbivorous fishes from northeastern New Zealand, butterfish Odax pullus (Labridae), marblefish Aplodactylus arctidens (Aplodactylidae), notch-head marblefish A. etheridgii (Aplodactylidae) and silver drummer Kyphosus sydneyanus (Kyphosidae), were examined using histology and transmission electron microscopy (TEM) to provide a detailed histological and ultrastructural description of gut anatomy. Gastric glands were distributed over rugae in the stomach of A. arctidens, A. etheridgii and K. sydneyanus. The luminal surface of the stomach of these three species was lined by columnar mucous cells, and oxynticopeptic cells lined the glands in the stomach. Villi were present along the length of the intestine in all four species. The anterior intestine had thin musculature, and was lined by absorptive cells with long microvilli and numerous small vesicles in the apical cytoplasm. The posterior intestine was lined by absorptive columnar cells with long microvilli, invaginations between microvilli with electron-dense membranes, and pinocytotic vesicles. Surface area generally decreased from the anterior to posterior intestine. Histological and ultrastructural results were consistent with lipid absorption occurring in the anterior GIT and protein absorption in the posterior GIT. The results of this study indicate clear differences in GIT structure among the study species, and digestion models based on chemical reactor theory were developed to characterise these differences.

A global meta‐analysis of temperature effects on marine fishes’ digestion across trophic groups

AbstractAimThe temperature constraint hypothesis proposes that marine herbivorous fishes are rare at high latitudes relative to carnivorous fishes because low temperatures impair the digestion of plant material. To test this hypothesis, we compared the effects of temperature on the digestive performance and investment in digestion of marine fishes across trophic groups.LocationGlobal marine ecosystems.Major taxa studiedMarine fishes.MethodsWe analysed data from 304 species consuming a range of diets to quantify the effects of temperature on three indicators of digestive performance and investment: gut passage time, absorption efficiency, and gut length.ResultsDecreasing temperatures increase gut passage time in fishes consuming macroalgae more than fishes consuming other fish or invertebrates. Low temperatures do not impair absorption efficiency in fishes regardless of diet, but herbivores have lower absorption efficiencies than carnivores overall. Gut length decreases with decreasing temperature in all trophic groups.Main conclusionsOur analyses reveal limited evidence to support the temperature constraint hypothesis. Low temperatures slow digestion more in fishes consuming macroalgae than those consuming animal prey; however, this may not reflect a meaningful disadvantage for herbivores but rather could be explained by greater representation of fishes relying on microbial fermentation at high latitudes. Herbivorous fishes absorb nutrients and energy from their food in similar proportions regardless of temperature, in contrast to the expectations of the temperature constraint hypothesis. Decreased gut length was associated with decreasing temperature across all trophic groups, likely due to improved food quality at high latitudes, which should benefit all trophic groups by reducing their required investment in gut tissues. Altogether, our findings run counter to the general hypothesis that low temperatures disadvantage the digestion of plant material and suppress the diversity and abundance of herbivorous fishes at high latitudes.

Does temperature constrain diet choice in a marine herbivorous fish?

The temperature constraint hypothesis (TCH) states that low water temperatures constrain the efficiency of algal digestion in fishes to an extent that limits the viability of herbivory. It is a widely cited explanation for the decline in diversity and abundance of marine herbivorous fishes at high latitudes. A key prediction of this hypothesis is that temperature-related physiological constraints may be ameliorated in free-living herbivores by a shift from herbivory to omnivory. We investigated this prediction by examining the diet of the primarily herbivorous marine fish Odax pullus (Labridae) at multiple locations spanning a gradient of 10° latitude and encompassing a change in median annual sea surface temperature of 5–7 °C. Foregut content and stable isotope analyses were used to compare diet across locations and results were evaluated against the prediction that a latitudinal temperature constraint on herbivory would result in significant variation in the composition of adult diets or the timing of an ontogenetic switch from omnivory to herbivory at colder, higher latitudes. We found that neither the proportion of animal material consumed nor ontogenetic changes in diet varied across the distributional range of this species in a manner consistent with the predictions of the TCH. This study demonstrates that water temperature does not constrain herbivory in a marine ectothermic herbivore and thus challenges a widely cited hypothesis.

Genomic and biochemical evidence of dietary adaptation in a marine herbivorous fish.

Adopting a new diet is a significant evolutionary change, and can profoundly affect an animal's physiology, biochemistry, ecology and genome. To study this evolutionary transition, we investigated the physiology and genomics of digestion of a derived herbivorous fish, Cebidichthys violaceus. We sequenced and assembled its genome (N50 = 6.7 Mb) and digestive transcriptome, and revealed the molecular changes related to digestive enzymes (carbohydrases, proteases and lipases), finding abundant evidence of molecular adaptation. Specifically, two gene families experienced expansion in copy number and adaptive amino acid substitutions: amylase and carboxyl ester lipase (cel), which are involved in the digestion of carbohydrates and lipids, respectively. Both show elevated levels of gene expression and increased enzyme activity. Because carbohydrates are abundant in the prickleback's diet and lipids are rare, these findings suggest that such dietary specialization involves both exploiting abundant resources and scavenging rare ones, especially essential nutrients, like essential fatty acids.

A new genus and species of the trematode family Gyliauchenidae Fukui, 1929 from an unexpected, but plausible, host, Kyphosus cornelii (Perciformes: Kyphosidae).

The Enenteridae Yamaguti, 1958 and Gyliauchenidae Fukui, 1929 exhibit an interesting pattern of host partitioning in herbivorous fishes of the Indo-West Pacific. Enenterids are known almost exclusively from fishes of the family Kyphosidae, a group of herbivorous marine fishes common on tropical and temperate reefs. In contrast, gyliauchenids are found in most of the remaining lineages of marine herbivorous fishes, but until the present study, had never been known from kyphosids. Here we report on the first species of gyliauchenid known from a kyphosid. Endochortophagus protoporus gen. nov., sp. nov. was recovered from the Western buffalo bream, Kyphosus cornelii (Whitley, 1944), collected off Western Australia. Kyphosus cornelii also hosts an enenterid, Koseiria allanwilliamsi Bray & Cribb, 2002, and is thus the first fish known in which enenterids and gyliauchenids co-occur. Molecular phylogenetic analyses place the new species close to those of Affecauda Hall & Chambers, 1999 and Flagellotrema Ozaki, 1936, but there is sufficient morphological evidence, combined with the unusual host, to consider it distinct from these genera. We discuss factors which may have contributed to the host partitioning pattern observed between enenterids and gyliauchenids.

Copper bioaccumulation and biokinetic modeling in marine herbivorous fish Siganus oramin

Marine herbivorous fish directly consume macroalgae, which commonly accumulate high levels of trace metals in polluted areas. We proposed that herbivorous fish could be better candidates for biomonitoring marine metal pollution than carnivorous fish. To date, the trophic transfer of Cu from macroalgae to marine herbivorous fish is unclear. In this study, the kinetics of Cu bioaccumulation in a widespread marine herbivorous fish, Siganus oramin, were investigated, and biokinetic modeling was applied to estimate the Cu levels in the fish sampled from different sites and seasons. The results showed that Cu accumulation in the fish was linearly correlated to the dietary Cu levels in the different prey species, which were proportional to the waterborne Cu concentrations. The Cu found in the subcellular trophically available metal fraction (TAM) in the prey contributed the largest proportion of accumulated Cu in S. oramin. The dietary assimilation efficiencies (AEs) of Cu were 15.56 ± 1.76%, 13.42 ± 2.86%, and 21.36 ± 1.47% for Ulva lactuca, Gracilaria lemaneiformis and Gracilaria gigas, respectively. The calculated waterborne uptake rate constant (ku) of Cu was 0.023 ± 0.011 L g−1 d−1, and the efflux rate constant (ke) was 0.055 ± 0.021 d−1. Dietary Cu accounted for 60%–75% of the body Cu in S. oramin, suggesting that dietary uptake could be the primary route for Cu bioaccumulation in herbivorous fish. The biokinetic model demonstrated that the Cu concentrations in the water and fish presented a positive linear relationship, which was in line with our field investigation along the coastal areas of South China. Therefore, we suggested that S. oramin could be used as a biomonitoring organism for Cu pollution in the marine environment. However, the heterogeneities between the predicted levels and the measured levels of Cu implied that seasonal changes should be taken into account to improve the accuracy of the model.

Comparative study of haematology of two teleost fish (Mugil cephalus and Carassius auratus) from different environments and feeding habits

Haematological parameters are valuable indicators of fish health status. This study is aimed to provide baseline data of the blood profile of two teleost fish species living in different environments and with divergent feeding behaviour, namely the flathead grey mullet Mugil cephalus Linnaeus, 1758, a marine herbivorous fish, and the goldfish Carassius auratus (Linnaeus, 1758), a freshwater omnivorous fish. Using an automated system coupled with flow cytometry and light microscopy, significant variations were found between M. cephalus and C. auratus blood parameters, except for haemoglobin concentration (Hgb). A significant increase in red blood cell count (RBC) and haematocrit (Hct) levels, associated with reduced mean corpuscular volume (MCV), was revealed in mullets in respect to goldfish. These data may be attributable to differences in fish species, or to their divergent physiological activeness as high RBC values are associated with fast movement and high activity with streamlined bodies, or to environmental factors such as water salinity, an increase in which may lead to erythropoiesis as an adaptive process in seawater fish. Additionally, lower values of white blood cell count (WBC) and thrombocyte count (TC) were recorded in mullets with respect to goldfish, and these changes may be due to divergent feeding habits of the two fish species, or to their different environments since increased salinity may inversely affect WBC. Overall, findings from this study provide a better understanding of the influences of divergent environmental conditions and feeding habits on fish blood parameters. The combined use of an automatic haematological count with flow cytometry was demonstrated to be effective for an early assessment of blood parameters in different fish species.

The nutritional basis of seasonal selective feeding by a marine herbivorous fish

Marine herbivorous fishes have the potential to significantly impact reef ecology through selective feeding on macroalgae. However, the nutritional drivers underlying their diet choice are often poorly understood. Here we examine diet, nutrient ingestion and assimilation in a marine herbivorous fish (Odax pullus; Labridae) endemic to temperate rocky reefs in New Zealand. Individuals were sampled across the year and across key life history stages to obtain a comprehensive insight into the nutritional consequences of feeding behaviour. Seasonal and ontogenetic changes in diet resulted in significant changes in the relative proportion of macronutrients ingested, and these changes coincided with periods of rapid somatic and reproductive tissue growth. In particular, protein and the sugar alcohol mannitol are likely to be important determinants of adult diets, and the seasonal availability of these nutrients is likely to be a key factor shaping the ecology and life history of this species.

Species of Tetrancistrum Goto & Kikuchi, 1917 (Monogenea: Dactylogyridae) from the gills of the whitespotted rabbitfish, Siganus canaliculatus (Park) (Perciformes: Siganidae) off Omani coasts, with a description of Tetrancistrum labyrinthus n. sp.

Tetrancistrum labyrinthus n. sp. is described from the gills of the marine herbivorous fish Siganus canaliculatus (Park) found in the Western Indian Ocean (Sea of Oman and Arabian Sea). Comparative morphological analyses of all previously described species of Tetrancistrum Goto & Kikuchi, 1917 confirmed the distinct status of T. labyrinthus n. sp. The new species closely resembles T. suezicum Paperna, 1972 and T. oraminii Young, 1967 in the morphology of the male copulatory organ. However, it can be distinguished by possessing a thin handle-like anterior basal flange and a compound accessory piece that is composed of a tapering rod-shaped anterior part and a large cylindrical, elongated posterior part. The new species can be further distinguished from other Tetrancistrum species by its highly sclerotised and complex disc-shaped vaginal vestibule. This is the first record of Tetrancistrum from the Sea of Oman and Arabian Sea, and the fourth of nominal species of Tetrancistrum known to parasitise Siganus canaliculatus (Park). In addition, T. indicum Paperna, 1972 is re-described here with an updated locality record.