Deep investigations of host-associated microbiota can illuminate microbe-based solutions to improve production in an unprecedented manner. The poor larval survival represents the critical bottleneck ...in sustainable marine aquaculture practices. However, little is known about the microbiota profiles and their governing eco-evolutionary processes of the early life stages of marine teleost, impeding the development of suitable beneficial microbial management strategies. The study provides first-hand mechanistic insights into microbiota and its governing eco-evolutionary processes in early life stages of a tropical marine teleost model,
.
The microbiota profiles and their dynamics from the first day of hatching till the end of metamorphosis and that of fingerling's gut during the routine hatchery production were studied using 16S rRNA amplicon-based high-throughput sequencing. Further, the relative contributions of various external factors (rearing water, live feed, microalgae, and formulated feed) to the microbiota profiles at different ontogenies was also analyzed.
A less diverse but abundant core microbial community (~58% and 54% in the whole microbiota and gut microbiota, respectively) was observed throughout the early life stages, supporting 'core microbiota' hypothesis. Surprisingly, there were two well-differentiated clusters in the whole microbiota profiles, ≤10 DPH (days post-hatching) and > 10 DPH samples. The levels of microbial taxonomic signatures of stress indicated increased stress in the early stages, a possible explanation for increased mortality during early life stages. Further, the results suggested an adaptive mechanism for establishing beneficial strains along the ontogenetic progression. Moreover, the highly transient microbiota in the early life stages became stable along the ontogenetic progression, hypothesizing that the earlier life stages will be the best window to influence the microbiota. The egg microbiota also crucially affected the microbial community. Noteworthily, both water and the feed microbiota significantly contributed to the early microbiota, with the feed microbiota having a more significant contribution to fish microbiota. The results illustrated that rotifer enrichment would be the optimal medium for the early larval microbiota manipulations.
The present study highlighted the crucial foundations for the microbial ecology of
during early life stages with implications to develop suitable beneficial microbial management strategies for sustainable mariculture production.
Cobia (Rachycentron canadum, Rachycentridae) is one of the prospective species for mariculture. The transcriptome-based study on cobia was hampered by an inadequate reference genome and a lack of ...full-length cDNAs. We used a long-read based sequencing technology (PacBio Sequel II Iso-Seq3 SMRT) to obtain complete transcriptome sequences from larvae, juveniles, and various tissues of adult cobia, and a single SMRTcell generated 99 gigabytes of data and 51,205,946,694 bases. A total of 8609435, 7441673 and 9140164 subreads were generated from the larval, juvenile, and adult sample pools, with mean sub-read lengths of 2109.9, 1988.2 and 1996.2 bp, respectively. All samples were combined to increase transcript recovery and clustered into 35661 high-quality reads. This is the first report on a full-length transcriptome from R. canadum. Our results illustrate a significant increase in the identified amount of cobia LncRNAs and alternatively spliced transcripts, which will help improve genome annotation. Furthermore, this information will be beneficial for nutrigenomics and functional studies on cobia and other commercially important mariculture species.
Fucoidan-rich seaweed extract (FRSE) was prepared from
Sargassum wightii
by modified alcohol-water extraction method. A 45-day feeding trial was conducted to evaluate the individual and combined ...effect of fucoidan-rich seaweed extract (FRSE—20 g kg
−1
) and exogenous α-amylase (100 mg kg
−1
) on the growth response, metabolic enzymes, immune parameters, and amylase gene expression of
Labeo rohita
. Four purified iso-nitrogenous diets (350 g CP kg
−1
feed) with different combinations of α-amylase were prepared. Among the various treatment groups, the group fed with FRSE along with amylase group exhibited significantly higher (
p
< 0.05) weight gain, SGR, PER, liver metabolic enzyme activities, and lower FCR than the control group. The hematological and serum parameters such as NBT, erythrocyte count, plasma protein, albumin and globulin values were significantly higher (
p
< 0.05) in the FRSE fed groups. LDH activities and antioxidant enzyme activities reduced significantly in FRSE fed groups, whereas activities were significantly higher (
p
< 0.05) in the α-amylase fed and control groups. The intestinal amylase activities were significantly higher in the α-amylase fed groups, while expression of amylase gene mRNA was significantly lower in the α-amylase-supplemented groups (
p
< 0.05). There was no significant difference between control and FRSE fed groups in both, intestinal amylase activities and amylase gene mRNA expression. Overall results confirmed that FRSE extracted from
S. wightii
enhances immune responses, but not the growth. Further, it does not show any evidence of an inhibitory effect on intestinal amylase activity as well as on the mRNA levels. Hence, the α-amylase supplementation at 100 mg kg
−1
with 20 g kg
−1
FRSE in
L. rohita
fingerlings diet provides growth-promoting effect without compromising its immune-modulating effect.
Populations of
Megalaspis cordyla (horse mackerel) from four areas, two each from the east (Digha and Mandapam regions in the Bay of Bengal) and west (Cochin and Mumbai regions of the Arabian Sea) ...coasts of the Indian peninsula, were studied using body shape morphometrics. A truss box method (
Strauss and Bookstein, 1982) was followed, and 33 distance variables were extracted from digital images of sample specimens using the software platforms tpsDig2 and PAST. The transformed truss measurements were subjected to factor analysis and classification by cross-validation of discriminant analysis. Measurements from the anterior half of the fish body showed meaningful loadings on the first factor, and those from the caudal peduncle gave high loadings on the second factor. The combination of distance variables that produced the minimum amount of misclassification consisted of variables belonging to the middle portion of the body. Our results indicated a clear separation of the Bay of Bengal and Arabian Sea populations. The Mumbai and Cochin populations exhibited obvious mixing, indicating the possible existence of a unique stock along the west coast of India. In the cross-validation of the morphometrics by discriminant analysis, the most well-defined group was the Mandapam population, with only 3.59% of the individuals being misclassified, followed by Digha, indicating limited gene flow in the Bay of Bengal populations of the horse mackerel. The strong morphometric differentiation observed between the Mandapam and Digha populations, in addition to the considerable coral reef features of the Gulf of Mannar region, suggests the existence of separate spawning stock populations of horse mackerel in these regions, which might require distinct stock assessment programs to provide effective management strategies for the east coast.
Hypoxia in aquatic environment is often a recurrent stressor which can affect growth and health of fishes. However, nutritional intervention can help aquatic animals to cope up with environmental ...stressors so as to alleviate the adverse effects. Here, we examined the impact of L-Arginine (Arg) supplementation on hypoxia-induced changes in immune responses and resistance to Aeromonas hydrophila infection in Indian Major Carp, Cirrhinus mrigala. The fish were fed with graded levels of Arg for 60 days and exposed to 72 h sublethal level of hypoxia (0.50 ± 0.16 mg/L dissolved oxygen DO). The six treatment groups with three replicates having different levels of Arginine such as N0.0 (0% Arg + Normoxia), H0.0 (0% Arg + Hypoxia), N0.7 (0.70% Arg + Normoxia), H0.7 (0.70% Arg + Hypoxia), N1.4 (1.40% Arg + Normoxia), and H1.4 (1.40% Arg + Hypoxia) were used in the study. Subsequently, the fish of different treatment groups were challenged with A. hydrophila. The hypoxia exposed fish exhibited significantly higher (P < .05) cumulative mortality compared to the unexposed fish, while Arg-fed groups showed reduced mortality irrespective of the level of dissolved oxygen. The albumin-globulin ratio, complement-3 response, respiratory burst, myeloperoxidase, serum antiprotease and lysozyme activities were significantly lower (P < .05) in hypoxia-exposed carp, revealing the increased susceptibility of fish to A. hydrophila is due to the immunosuppressive effect of hypoxia, which was improved in Arg-supplemented groups. We conclude that there is a possible role of hypoxia in sporadic outbreaks of bacterial diseases in carps as acute hypoxia causes immunosuppression which can be reversed by 0.7% Arg supplementation.
•The susceptibility of Cirrhinus mrigala to Aeromonas hydrophila increased due to hypoxia.•Arginine fed groups showed reduced mortality with Aeromonas hyrophila challenge.•The non-specific immune parameters were decreased (P < .05) due to hypoxia.•Arginine feeding restored the hypoxia-induced reduction in non-specific immune parameters.
► Separate stocks of
Decapterus russelli from east and west coast of India. ► Separation likely due to geographical barrier and different hydrological conditions. ► Overlapping of the stocks within ...the coasts was observed. ► Separate management strategy for each stock is needed for sustainability. ► Molecular and biochemical methods can further confirm the present observation.
Decapterus russelli (Indian Scad) is an important pelagic carangid distributed on both east and west coast of India. Despite its wide distribution, the stock structure of the species is not well known. The present study was conducted to investigate stock structure of
D. russelli, based on body shape morphometrics using truss network system. A total number of 360 samples of the species were collected from two centres, Digha and Visakhapatnam in Bay of Bengal from east coast and on the west coast from Mumbai and Cochin in Arabian Sea. A truss network was constructed by interconnecting 11 landmarks to form a total of 23 distance variables extracted from digital images of samples using tps Dig2 and PAST software platforms. The transformed truss measurements were subjected to factor analysis and classification by cross-validation of discriminant analysis. Factor analysis showed meaningful loading of the middle portion, the portion below the second dorsal fin, above anal fin, and the caudal portion on first and second factor, respectively. The factor analysis revealed the existence of two morphologically different stocks of
D. russelli between east and west coast of India. The discriminant analysis was conducted by the combination of the truss distances that loaded on Factor-1 and Factor-2. The measurements that belonged to the middle portion and caudal portion of the body produced minimum misclassification rate of 5% between the coasts; whereas, the misclassification was 28% for all the four stocks. The misclassification was higher between the stocks within the coast. The high rate of misclassification observed within the coast is probably the result of no demarcation in fishing area. The occurrence of a separate stock on each coast may be the result of different physical and ecological condition of Bay of Bengal and Arabian Sea.
Cobia (Rachycentron canadum) is a high-value marine aquaculture species. Knowledge of the microbial dynamics in various aquaculture operations is crucial for developing suitable management practices. ...The present study revealed the critical dysbiotic events in the whole larval and juvenile-gut microbiome of cobia, through an inevitable aquaculture operation, viz. live transportation. The results through both culture-dependent and independent techniques demonstrated the sensitivity of the cobia microbiome during early life, where live transport is inevitable. In detail, there was a significant change in the microbial composition and reduction in the cultivable load of all the life stages. Further, a significant reduction in functional metagenomics along with an increase in taxonomic metagenomics was recorded in the L21 stage. Significant reductions of the putative healthy microbiota, viz., Proteobacteria and Actinobacteria were remarkable in the whole larval microbiome. The analysis through linear discriminant analysis effect size revealed that the opportunistic fish pathogens, viz., Vibrio spp., Arcobacter spp., and Acinetobacter spp. were increased whereas, Pseudomonas spp. was decreased in larvae following transportation. The significant reduction in the taxonomic diversity measures was noteworthy in the juvenile-gut microbiome. Transportation promoted Serratia spp., Enterobacter spp., an unidentified genus in Flavobacteriaceae, Pseudoalteromonas spp., Alteromonas spp., and Enterovibrio spp., and inhibited Empedobacter spp. in the juvenile gut. Collectively, the results provide the prospective metagenomic signatures of health and stress in the early life stages of cobia and novel possible explanations for increased disease susceptibility post-transportation. The study warrants future research on the microbes which were found to be decreased following transportation, as potential probiotics to mitigate the stress in the marine aquaculture practices. The metagenomic signatures revealed through the study can be further applied for evaluating different husbandry practices to mitigate stress during live transportation.
•First data on gut microbial dynamics following transportation in marine fish•Displays probiotic microbes to design fish health improvisation strategies•Decodes novel reasons for increased disease susceptibility post-transportation•Provides metagenomic signatures of health and stress in early life stages of cobia•Generates insights on the whole larval and juvenile gut microbiome of cobia
Fish assemblage structure in Palair reservoir, a medium tropical reservoir along the river Paleru, a tributary of river Krishna in Southern India, was studied along the spatial gradient of the ...impoundment. The abundance and assemblage structure of wild fish aggregated around the fish cage units installed in the reservoir were assessed and compared with other sites. Seasonal sampling was carried out and fish community structure in terms of species composition and abundance, trophic guild, niche, tolerance, resilience and conservation status were analyzed. A total of 38 fish species were recorded wherein the family Cyprinidae dominated in the number of species (15) followed by Cichlidae and Channidae (3 each). Margalef richness index (d), Pielou’s evenness index (J’), Simpson’s index (1-λ) and Shannon index (H’) revealed significant variation across different zones. Species richness was maximum in the Site1 (d = 4.44–5.12), whereas the abundance of individuals was maximum at Site4 (H’ = 2.65–2.86) i.e. near cage in the lacustrine zone. The important species contributing to the dissimilarities among the zones were identified and percentage of their contribution was estimated using SIMPER analysis. Trophic guild of fishes indicated the dominance of omnivorous species followed by carnivores, indicating the heterotrophic phase of the reservoir. The spatial and seasonal variations in the fish assemblage structure were tested applying statistical analyses such as PERMANOVA and nMDS. The results indicated a positive impact of cage farming in supporting the wild fish fauna, influencing the large aggregations of fishes around the cages. The temporal variability in the cage-associated fish assemblage was related to recruitment periods of juveniles (e.g. E. maculates and E. suratensis in summer, and S. seenghala in monsoon seasons). The links between fish assemblages and environmental parameters were explored through DISTILM and the deterministic factors for fish abundance in the reservoir were phosphate, pH, dissolved Oxygen, total hardness and depth. The study also indicated the impacts of cage culture with record of accidental escapes of farmed fish to the reservoir system. The baseline information generated and recommendations formulated in the study are crucial for the conservation of fish diversity, fisheries enhancement and management planning of tropical peninsular reservoirs.
Summary
Harpadon nehereus, commonly known as ‘Bombay duck’, is a fish with a discontinuous distribution along the Indian peninsula. The fisheries are dominant on the north‐east and north‐west coast ...but are absent in commercial landings below 15° north latitude. Heretofore stock assessment studies had not considered the various spawning stock components that replenish this fishery, therefore the present study. Fish samples were collected from four locations: two each from the northeast and the northwest coasts. Twenty‐four morphometric variables were measured using a box‐truss network method. Factor analysis of these variables differentiated the east and the west coast fish populations. Multiple comparisons on the factor scores indicated two independent stocks on the east coast, whereas the fishery on the west coast is replenished by a single stock. The important morphometric traits that accounted for most of the stock variations were related to swimming adaptations of the fish. Future stock assessments can consider the population on the west coast as a single stock when formulating management plans. To harvest the resource in a sustainable manner, the maritime states on the west coast should adopt collaborative efforts towards managing this fishery.
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