Effects of diet composition on gut microbiome and mercury biotransformation in the gobyfish.

Mercury (Hg) biotransformation (methylation and demethylation) could play a key role in affecting the final Hg speciation and level in fish. The gut microbiota was identified to be involved in this process. Diet is recognized to greatly influence the gut microbiome, whereas the impact of food composition on Hg biotransformation in fish has yet to be addressed. The study investigated the biotransformation and bioaccumulation of Hg in the gobyfish (Mugilogobius chulae) under different food choices (natural prey and artificial food) and evaluated the role of gut microbiome in these processes. The results showed that different diet composition significantly affected the gut microbiome and subsequently resulted in varied phenomenon of Hg biotransformation within fish body. Significant demethylation (0.33 % d-1) was only observed in the natural prey (brine shrimp) treatment, whereas methylation was occurred extremely slowly (0.013 % d-1) only in the artificial food (commercial dry pellets) treatment. Furthermore, the growth of demethylators was also enhanced in the natural prey treatment, which contributed to the demethylation process in fish. Furthermore, the gut microbial structure of gobyfish was greatly altered by different diet composition. This study highlights the significance of food choices in the minimization of Hg contamination in aquaculture. Incorporating natural prey into fish diets could be a better choice to balance the fish production and control MeHg levels. CAPSULE: Diet composition greatly affects the gut microbial composition, and natural prey could help to reduce the potential of MeHg accumulation by fish.

Interpopulation trophic niches and ontogenetic shifts of a mangrove fish predator.

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub-adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub-adult stages. The results revealed that both δ13 C and δ15 N values varied greatly across populations and between ontogenetic groups, and complex spatio-ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub-adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial-ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems.

Prey-specific determination of arsenic bioaccumulation and transformation in a marine benthic fish.

The sediments from Chinese coastal waters contain relatively high concentrations of arsenic (As), mainly arsenate As(V), which may be transferred along the marine benthic food chain. The prey-specific determination of As bioaccumulation and transformation in marine benthic fish remains little known. In this study, we focused on a typical marine benthic food chain comprising of sediments, deposit-feeding invertebrates (polychaete Nereis succinea and clam Gafrarium tumidum) and goby fish Mugilogobius chulae. Graded exposed experiments using different As exposure durations and concentrations were conducted to examine their transformation rate and efficiency. Radiotracer techniques were used to determine the rates of As uptake (as arsenate) from seawater, assimilation from two prey and its subsequent efflux in the goby fish. We demonstrated that the two prey (polychates and clams) displayed different As biotransformation in the goby fish. Biotransformation rate was higher in the goby fish fed on the clams than on the polychaetes, and biotransformation efficiency was lower with increasing inorganic As concentration in the prey. The As overall bioaccumulation in the goby fish was very low, mainly because of the low dissolved uptake and dietary assimilation and high efflux. Combining the biotransformation and biokinetics measurements, our findings highlighted that different prey containing different As concentrations and As species resulted in the comparable As bioaccumulation in the goby fish.

DNA barcoding of Gobiid fishes (Perciformes: Gobiidae) from eastern and northeastern India with new record of a Gobionellinae species for the region.

The study attempted identification of Gobiid fishes from freshwaters in the east and northeast India on a collection of 20 specimens. The DNA barcode data delineated the collected samples into three species clades in the neighbor-joining tree. The results confirmed the identification of five sample sequences belonging to the subfamily Gobionellinae due to cohesive cladding with Awaous congeners. This is a new subfamily record for the northeastern region. Another 15 sample sequences showed conspecific cladding with Glossogobius giuris in the database. Among the 15 sample sequences, 14 sequences cladded with G. giuris sequences of Indian specimens while one sample sequence cladded with G. giuris sequences of South African specimens. This indicated the presence of either a hidden species or a previously synonymized species in the G. giuris complex.

Ameliorating effects of goby fish protein hydrolysates on high-fat-high-fructose diet-induced hyperglycemia, oxidative stress and deterioration of kidney function in rats.

This study investigated the therapeutic potential of undigested goby fish (Zosterisessor ophiocephalus) muscle proteins (UGP) and their hydrolysates on high-fat-high-fructose diet (HFFD)-fed rats. HFFD induced hyperglycemia, manifested by a significant increase in the levels of glucose and glycogen as well as α-amylase activity when compared to normal rats. The administration of GPHs to HFFD-fed rats significantly decreased α-amylase activity and the contents of blood glucose and hepatic glycogen. By contrast, the UGP increased the glucose metabolic disorders in HFFD-fed rats. Furthermore, HFFD-fed rats showed oxidative stress, as evidenced by decreased antioxidant enzyme activities and glutathione (GSH) levels and increased concentration of the lipid peroxidation product malondialdehyde in liver and kidney. Interestingly, the daily gavage of UGP and GPHs improved the redox status in liver and kidney of HFFD-rats by ameliorating or reversing the above-mentioned changes. Moreover, GPHs exhibited a renal protective role by reversing the HFFD-induced decease of uric acid and increase of creatinine levels in serum and preventing some HFFD-induced changes in kidney architecture. The results demonstrate that GPHs contain bioactive peptides that possess significant hypoglycemic and antioxidant properties, and ameliorate renal damage in rats fed hypercaloric diet.

Proteomic analysis of cardiac response to thermal acclimation in the eurythermal goby fish Gillichthys mirabilis.

Cardiac function is thought to play a central role in determining thermal optima and tolerance limits in teleost fishes. Investigating proteomic responses to temperature in cardiac tissues may provide insights into mechanisms supporting the thermal plasticity of cardiac function. Here, we utilized a global proteomic analysis to investigate changes in cardiac protein abundance in response to temperature acclimation (transfer from 13°C to 9, 19 and 26°C) in a eurythermal goby, Gillichthys mirabilis. Proteomic data revealed 122 differentially expressed proteins across acclimation groups, 37 of which were identified using tandem mass-spectrometry. These 37 proteins are involved in energy metabolism, mitochondrial regulation, iron homeostasis, cytoprotection against hypoxia, and cytoskeletal organization. Compared with the 9 and 26°C groups, proteins involved in energy metabolism increased in 19°C-acclimated fish, indicating an overall increase in the capacity for ATP production. Creatine kinase abundance increased in 9°C-acclimated fish, suggesting an important role for the phosphocreatine energy shuttle in cold-acclimated hearts. Both 9 and 26°C fish also increased abundance of hexosaminidase, a protein directly involved in post-hypoxia stress cytoprotection of cardiac tissues. Cytoskeletal restructuring appears to occur in all acclimation groups; however, the most prominent effect was detected in 26°C-acclimated fish, which exhibited significantly increased actin levels. Overall, proteomic analysis of cardiac tissue suggests that the capacity to adjust ATP-generating processes is crucial to the thermal plasticity of cardiac function. Furthermore, G. mirabilis may optimize cellular functions at temperatures near 19°C, which lies within the species' preferred temperature range.

A cytogenetical study on Economidichthys pygmaeus Holly, 1929 (Pisces, Gobiidae), an endemic freshwater goby from Western Greece.

A cytogenetic study was carried out on the chromosomes and the nuclear DNA content of the freshwater goby Economidichthys pygmaeus (Pisces, Gobiidae). The species is characterized by a 2n=46 karyotype consisting of 12 submetacentric and 11 subtelocentric chromosome pairs (NF=70). Major (45S) rDNA genes are terminal-centromeric located on the short arm of a single medium-small sized submetacentric pairas assessed by in situ hybridization, CMA3 staining, and Ag-NOR banding. The haploid (C-value) nuclear DNA content is 0.93±0.003 picograms. The cytogenetical data of Economidichthys pygmaeus were compared with those ones already available for other related gobies.