Vertebral column regionalisation in Chinook salmon, Oncorhynchus tshawytscha

Teleost vertebral centra are often similar in size and shape, but vertebral-associated elements, i.e. neural arches, haemal arches and ribs, show regional differences. Here we examine how the presence, absence and specific anatomical and histological characters of vertebral centra-associated elements can be used to define vertebral column regions in juvenile Chinook salmon (Oncorhynchus tshawytscha). To investigate if the presence of regions within the vertebral column is independent of temperature, animals raised at 8 and 12 °C were studied at 1400 and 1530 degreedays, in the freshwater phase of the life cycle. Anatomy and composition of the skeletal tissues of the vertebral column were analysed using Alizarin red S whole-mount staining and histological sections. Six regions, termed I-VI, are recognised in the vertebral column of specimens of both temperature groups. Postcranial vertebrae (region I) carry neural arches and parapophyses but lack ribs. Abdominal vertebrae (region II) carry neural arches and ribs that articulate with parapophyses. Elastic- and fibrohyaline cartilage and Sharpey's fibres connect the bone of the parapophyses to the bone of the ribs. In the transitional region (III) vertebrae carry neural arches and parapophyses change stepwise into haemal arches. Ribs decrease in size, anterior to posterior. Vestigial ribs remain attached to the haemal arches with Sharpey's fibres. Caudal vertebrae (region IV) carry neural and haemal arches and spines. Basidorsals and basiventrals are small and surrounded by cancellous bone. Preural vertebrae (region V) carry neural and haemal arches with modified neural and haemal spines to support the caudal fin. Ural vertebrae (region VI) carry hypurals and epurals that represent modified haemal and neural arches and spines, respectively. The postcranial and transitional vertebrae and their respective characters are usually recognised, but should be considered as regions within the vertebral column of teleosts because of their distinctive morphological characters. While the number of vertebrae within each region can vary, each of the six regions is recognised in specimens of both temperature groups. This refined identification of regionalisation in the vertebral column of Chinook salmon can help to address evolutionary developmental and functional questions, and to support applied research into this farmed species.

Gastric dilation and air sacculitis in Chinook salmon, Oncorhynchus tshawytscha (Walbaum); correlation of macroscopic and microscopic lesions, and relationship of the syndrome to glomerulonephritis and serum biochemistry

Macroscopic and microscopic assessment procedures were developed to evaluate the severity and enable diagnosis from histological samples, of gastric dilation and air sacculitis (GDAS) in Chinook salmon, Oncorhynchus tshawytscha. Stomachs and swim bladders were examined from young fish with experimentally induced GDAS and from larger fish with the syndrome held in commercial saltwater net-pens. Fish fed a diet previously known to induce GDAS had significantly wider stomachs with decreased prominence of longitudinal stomach folds that contained larger amounts of fluid (P < 0.001), and thinner stomach walls with greater inter-nerve distances (P < 0.001), than fish fed an alternative commercial diet not associated with the syndrome. These fish also had swim bladders that were more likely to be opaque and contain more fluid (P < 0.001). These observations correlated well with selected criteria for stomach tissue (P < 0.002) and swim bladder (P < 0.04) that could be evaluated microscopically. Four stomach measurements, primarily measurements of wall or partial wall thickness and inter-nerve distances, were suitable for discriminating between affected and non-affected fish. A stomach width ratio, that was independent of fish weight and highly correlated with macroscopic stomach measurements (P < 0.0001), was particularly useful; this ratio was derived from the distances between both the outer border of the muscularis mucosa and mesothelium of the serosal surface to the stratum compactum. Serum biochemistry parameters (osmolality, calcium and magnesium) did not differ between fish fed different diets, but serum creatinine concentration was correlated with the microscopic thickness of the muscularis externa of the stomach wall and the total stomach thickness (P < 0.001 and P < 0.003, respectively). A glomerulonephritis was also noted in these fish. The severity of the lesion was not significantly related to GDAS nor to any serum biochemistry parameter assayed however.

Experimental production of gastric dilation and its association with osmoregulatory stress and biogenic amines in chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Chinook salmon smolt in fresh water fed a commercial diet known to produce minimal gastric dilation and air sacculitis (GDAS) were randomly assigned to four experimental tanks with flow-through sea water. All four groups were acclimatized to sea water for 3 weeks and fed a diet of minced fresh seafood. After 3 weeks the groups were fed either; seafood as before, a different commercial pelleted diet associated with the development of GDAS on farms, or either diet supplemented with 500 mg L(-1) putrescine, 300 mg L(-1) cadaverine and 250 mg L(-1) tyramine. Gastric dilation was produced in fish fed the commercial diet for 1 month but not by feeding a diet of minced seafood. The addition of putrescine, cadaverine and tyramine to either diet had no significant effect on the development of gastric dilation. Fish fed the commercial diet had significantly (P < 0.0001) wider weight-adjusted stomach widths, less prominent longitudinal stomach folds (P < 0.0001) and lower (P < 0.0001) stomach-width ratios than fish fed the fresh seafood diet. There was no significant difference in serum osmolality or sodium concentration between fish from groups with or without gastric dilation or fed biogenic amines.