Gene expression profiling of trout muscle during flesh quality recovery following spawning

Background Sexual maturation causes loss of fish muscle mass and deterioration of fillet quality attributes that prevent market success. We recently showed that fillet yield and flesh quality recover in female trout after spawning. To gain insight into the molecular mechanisms regulating flesh quality recovery, we used an Agilent-based microarray platform to conduct a large-scale time course analysis of gene expression in female trout white muscle from spawning to 33 weeks post-spawning. Results In sharp contrast to the situation at spawning, muscle transcriptome of female trout at 33 weeks after spawning was highly similar to that of female trout of the same cohort that did not spawn, which is consistent with the post-spawning flesh quality recovery. Large-scale time course analysis of gene expression in trout muscle during flesh quality recovery following spawning led to the identification of approximately 3340 unique differentially expressed genes that segregated into four major clusters with distinct temporal expression profiles and functional categories. The first cluster contained approximately 1350 genes with high expression at spawning and downregulation after spawning and was enriched with genes linked to mitochondrial ATP synthesis, fatty acid catabolism and proteolysis. A second cluster of approximately 540 genes with transient upregulation 2 to 8 weeks after spawning was enriched with genes involved in transcription, RNA processing, translation, ribosome biogenesis and protein folding. A third cluster containing approximately 300 genes upregulated 4 to 13 weeks after spawning was enriched with genes encoding ribosomal subunits or regulating protein folding. Finally, a fourth cluster that contained approximately 940 genes with upregulation 8 to 24 weeks after spawning, was dominated by genes encoding myofibrillar proteins and extracellular matrix components and genes involved in glycolysis. Conclusion Overall, our study indicates that white muscle tissue restoration and flesh quality recovery after spawning are associated with transcriptional changes promoting anaerobic ATP production, muscle fibre hypertrophic growth and extracellular matrix remodelling. The generation of the first database of genes associated with post-spawning muscle recovery may provide insights into the molecular and cellular mechanisms controlling muscle yield and fillet quality in fish and provide a useful list of potential genetic markers for these traits.

Riverbed Substrate Requirements for Natural Reproduction of Gymnocypris przewalskii

Gymnocypris przewalskii (i.e., Qinghai Lake naked carp) is a migratory fish species that lives in highland brackish water. It is important to understand the abiotic environment required by this fish to reproduce naturally so that its habitat can be protected and the wild population can be conserved. Here, artificial simulation and spawning ground substrate transformation experiments were conducted to examine the riverbed substrate requirements for G. przewalskii to naturally reproduce. Using various techniques (in vitro markers, videography, and Ethovision XT behavior tracking), this study systematically investigated the riverbed substrate preferences of G. przewalskii as well as the characteristics and effectiveness of natural reproduction induced by pebble riverbed substrate. The findings can be summarized as follows: (1) the habitat preferences of G. przewalskii differed significantly between various riverbed substrate, with pebble substrate being preferred during natural reproduction, and sand substrate being preferred pre- and post-spawning, and (2) the natural reproduction of G. przewalskii was heavily reliant on pebble riverbed substrate. Specifically, pebble substrate significantly improved spawn quantity and fertilization rate. These findings provide scientific evidence for the improvement and restoration of G. przewalskii spawning grounds, and insights regarding the artificial bionic reproduction of G. przewalskii.

Food web incorporation of marine-derived nutrients after the reintroduction of endangered inner Bay of Fundy Atlantic salmon (Salmo salar)

Inner Bay of Fundy Atlantic salmon (Salmo salar) are endangered anadromous fish that have the potential to provide marine-derived nutrients (MDNs) to freshwater ecosystems depending on their population abundance. Salmon have been reintroduced to the Upper Salmon River, but not the adjacent Point Wolfe River, in Fundy National Park, New Brunswick, Canada. This study determined whether stocking of adult salmon increased the productivity of the river. To examine the incorporation of MDNs, biofilm, leaf litter, Perlidae, Heptageniidae and brook trout (Salvelinus fontinalis) were sampled pre- and post-spawning in 2015-2017 from down- and up-stream of a natural barrier in both rivers and analyzed for carbon (δ13C) and nitrogen (δ15N) isotopes. After salmon spawning in each year, all organisms at the downstream site of the stocked river increased in δ13C and δ15N, with the greatest enrichment in brook trout (δ13C -23.97 to -21.10‰, δ15N +6.36 to +10.73‰). The proportion of MDNs in brook trout after salmon spawning (2015: 23.4%, 2016: 40.7%, 2017: 37.4%) also increased with higher numbers of released adult salmon. Results support the importance of salmon restoration for increasing the proportion of MDNs and productivity in rivers in Atlantic Canada.

The dynamics of the liver weight and liver indices in the course of gonad maturation of gadid species on Eastern Kamchatka

Longterm data on the liver weight, hepatosomatic (HSI) and gonadosomatic (GSI) indices of walleye pollock, Pacific cod and saffron cod are analyzed on Eastern Kamchatka in seasonal aspect and in the course of gonad maturation. Individual values of the indices extensively vary and depend on the fish body length, season and stage of gonad maturity. The dynamics of the HSI is agree to the dynamics of the GSI during the year and depending on gonad maturity. The maximum values of the HSI are typical for walleye pollock and Pacific cod individuals with the gonads of the III stage of maturity. The maximum values of the index in saffron cod are found in mature individuals with immature gonads. The minimum values are demonstrated by the fish with the gonads at the stage of final spawning or of post-spawning recovery. During the annual reproduction cycle males and females of walleye pollock and cod realize different scenarios of spending and accumulating liver fat. Whereas the maximum HSI is observed in the fish with the gonads at the III maturity stage, the minimum values in males are typical for individuals with smelting gonads, and in females – on finishing the spawn. That can be connected to possible feeding for the individual. Liver weight and liver index can increase in males just shortly after finishing spawning, in females that is found only at the stage of post-spawning recovery.

Ideal free eagles: Bald Eagle distribution in relation to salmon availability on four salmon spawning rivers

The movement of individuals according to the availability of resources has a fundamental effect on animal distributions. In the Pacific Northwest, Bald Eagles (Haliaeetus leucocephalus (Linneaus, 1766)) rely heavily on scavenging opportunities during the non-breeding period, and their distribution and movements are thought to be strongly influenced by the availability of post-spawning Pacific salmon (genus Oncorhynchus Suckley, 1861) carcasses. We surveyed the abundance of eagles and salmon on four adjacent rivers on Vancouver Island, British Columbia, Canada, during the 2017 fall spawning season. Salmon began to arrive in late September, peaked in abundance in mid-November, and were absent after early December. The seasonal progression of Bald Eagle abundance matched that of salmon carcass availability. The slope of proportional eagle – salmon relationship was significantly positive, though lower than the 1:1 match predicted by Ideal Free Distribution theory. The numerical response of Bald Eagles to salmon abundance was elevated on one of the rivers, potentially due to physical features such as sandbars and mudflats that increased the availability of carcasses and provided access points for eagles.

ECOLOGICAL AND MORPHOLOGICAL CHARACTERISTICS OF NEMATODES OF THE GENUS RHABDOCHONA, PARASITES OF THE MARINKA

The article presents results of the study of morphology and ecology of 3 species of nematodes of the genus Rhabdochona, which parasitize on the marinka, a typical representative of the Nagorno-Asian fauna of fish. We collected material from the species of Rhabdohona parasitizing on the marinka in the basin of the upper reaches of the Syrdarya River, in the mountain rivers Isfayramsay, Sokh and Shakhimardansay located in the south of the Fergana Valley, as well as in the mountain rivers Chodaksay and Rezaksay located in the north of the Valley. Features of morphology of the species Rabdochona denudata, Rh. gnedini and subspecies Rh. hellichi turkestanica were described based on the study results. The characterized species differ from each other in a number of characters, including the size of the body and the spicule, and the tail and egg shape. Nevertheless, there is still a considerable amount of work to be done for molecular and genetic identification of various forms of the species Rh. hellichi. The marinka that shows high morpho-ecological variability under the conditions of the study area, is a polyphage, which contributes to the fish infecting with nematodes, especially during the period of active post-spawning feeding. The nematode Rh. hellichi turkestanica (Skryabin, 1917) was considered a subspecies and is observed in the original form of this helminth and is recorded in Uzbekistan for the first time.

Gender Differences in Hemocyte Immune Parameters of Hong Kong Oyster Crassostrea hongkongensis During Immune Stress

Gender differences in individual immune responses to external stimuli have been elucidated in many invertebrates. However, it is unclear if gender differences do exist in the Hong Kong oyster Crassostrea hongkongensis, one of the most valuable marine species cultivated along the coast of South China. To clarify this, we stimulated post-spawning adult C. hongkongensis with Vibrio harveyi and lipopolysaccharide (LPS). Gender-based differences in some essential functional parameters of hemocytes were studied via flow cytometry. Obvious gender-, subpopulation-, and immune-specific alterations were found in the hemocyte immune parameters of C. hongkongensis. Three hemocyte subpopulations were identified: granulocytes, semi-granulocytes, and agranulocytes. Granulocytes, the chief phagocytes and major producers of esterase, reactive oxygen species, and nitric oxide, were the main immunocompetent hemocytes. Immune parameter alterations were notable in the accumulation of granulocyte esterase activities, lysosomal masses, nitric oxide levels, and granulocyte numbers in male oysters. These results suggest that post-spawning-phase male oysters possess a more powerful immune response than females. Gender and subpopulation differences in bivalve immune parameters should be considered in the future analysis of immune parameters when studying the impact of pathogenic or environmental factors.