Development and physiology of gastric dilation air sacculitis in Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Abstract

The syndrome known as gastric dilation air sacculitis (GDAS) has previously been shown to affect Chinook salmon, Oncorhynchus tshawytscha, in seawater (SW) aquaculture. Feed and osmoregulatory stress have been implicated as potential epidemiological co-factors. The development and physiology of GDAS was investigated in SW and freshwater (FW) adapted smolts. Diet A (low-cohesion pellets) and diet B (high-cohesion pellets) were fed to both FW- and SW-adapted fish. GDAS was induced only in the SW trial on feeding diet A. Stimulated gastro-intestinal (GI) smooth muscle contractility, and fluid transport by the pyloric caeca were different in GDAS-affected fish, which also showed osmoregulatory dysfunction. Cardiac stomach (CS) smooth muscle contractility in response to acetylcholine and potassium chloride (KCl) was significantly reduced in fish fed diet A relative to controls from weeks 3-5. In contrast, maximal pyloric sphincter (PS) circular smooth muscle contraction in response to KCl was significantly elevated in fish fed diet A in weeks 4 and 5. Serum osmolality was elevated in GDAS-affected fish from week 2 of the SW trial. Fluid transport from the mucosal to serosal surface of isolated pyloric caeca was significantly reduced in weeks 3, 4 and 5 in SW fish fed diet A. Gastric evacuation from the stomach of healthy fish was shown to be significantly different when diets of low- and high-cohesion were fed. The results are consistent with the intestinal brake playing a role in the development of the disease.

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

“…The present study reinforces previous observations (Lumsden et al. 2003; Forgan & Forster 2007) that the syndrome is highly influenced by diet. At the single time point examined in the present study, fish that were fed the commercial diet previously associated with the development of GDAS had stomachs and swim bladders in relatively poorer condition by most of the criteria employed.…”

“…Fish that were then switched to extruded feeds from a different manufacturer and reassessed had less severe lesions in the stomach and swim bladder than did fish that were maintained on the original diet (unpublished data). In the present study, diets A and B did not differ in proximate analysis, lipid/amino acid or metal content, but other authors have demonstrated that the physical qualities of the pellet, particularly the cohesiveness of the pellet rather than the chemical composition, is likely one of the most important factor(s) that influence the enterogastric cycle/pyloric brake and the pathogenesis of GDAS (Forgan & Forster 2007).…”

“…Later, Forgan & Forster (2007) were also able to reproduce GDAS in a large population and show that low physical pellet cohesion was the most important dietary property responsible for inducing GDAS in saltwater‐raised Chinook salmon. Feeding low‐cohesion diets led to a reduced rate of fluid transport from the mucosal to the serosal surface of pyloric caeca and an increase in serum osmolality, while contractility declined in cardiac stomach muscle but increased in the pyloric sphincter (Forgan & Forster 2007). Observations regarding serum osmolality are somewhat equivocal, however, other authors have noted no difference in osmolality between GDAS‐affected and non‐affected fish up to 30 days post‐transfer to salt water, despite the condition becoming grossly apparent after 10 days (Lumsden et al.…”

“…GDAS was first reproduced using a commercially produced diet, albeit with a small number of fish (Lumsden, Marshall, Gillard, Wybourne & Minamikawa 2003). Later, Forgan & Forster (2007) were also able to reproduce GDAS in a large population and show that low physical pellet cohesion was the most important dietary property responsible for inducing GDAS in saltwater-raised Chinook salmon. Feeding lowcohesion diets led to a reduced rate of fluid transport from the mucosal to the serosal surface of pyloric caeca and an increase in serum osmolality, while contractility declined in cardiac stomach muscle but increased in the pyloric sphincter (Forgan & Forster 2007).…”

Relationship between gut microbiota and Chinook salmon (Oncorhynchus tshawytscha) health and growth performance in freshwater recirculating aquaculture systems

“…Particularly, A. hydrophila has been associated with swim bladder infections in wild freshwater fish ( Teskeredžić et al, 2000 ) and has been associated with gastric dilation and air sacculitis (GDAS) in Chinook salmon farmed in the marine environment ( Lumsden et al, 2002 ). Referring to previous studies ( Lumsden et al, 2002 ; Forgan and Forster, 2007a , b ), it is possible that the diet retention properties may have been an issue in this trial and could have led to swim bladder fluid accumulation, even though the trial was in freshwater.…”