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Figure 3 | BMC Physiology

Figure 3

From: Intestinal barrier function of Atlantic salmon (Salmo salar L.) post smolts is reduced by common sea cage environments and suggested as a possible physiological welfare indicator

Figure 3

Intestinal barrier function after long term hypoxia (Experiment 1). This experiment aimed at mimicking an overall situation often found in sea cages when water flow decreases and DO levels are reduced to levels as low as around 50%. Decreased water exchange rate may also cause increased concentrations of toxic metabolites. Four fish from each tank in triplicate was sampled between days 41-43, from 80% and 50% DO levels groups created by adjusting inflow (range 41-137 L min-1) in response to oxygen consumption of the fish. The intestine was removed and opened longitudinally, divided into a proximal and a distal part, washed in ice-cold salmon Ringer solution and mounted in Ussing chambers. The electrical parameters; transepithelial resistance (TER), short-circuit current (SCC) and transepithelial potential (TEP) were measured. TER is mainly a measure of the paracellular permeability, and SCC describes the sum of active transports. This, together with the passive leakage of charged molecules across the epithelium is reflected in the TEP. The paracellular permeability of the intestinal epithelium was also assessed as the apparent permeability (Papp) of a well documented paracellular marker 14C-mannitol. Ussing chamber data was analysed using a genral linear model with intestinal region and treatment (with tank nested within treatment) as factors. Paracellular permeability was higher in both intestinal regions in the 50% DO group as indicated by decreased TER (p < 0.05) (A) and the increased Papp for mannitol which increased in both the proximal and distal intestine (p < 0.05) (B). No major differences were observed in TEP (C) or SCC (D). All data are expressed as means ± SEM and p < 0.05 was regarded as significant and indicated as *, p < 0.01 as ** and p < 0.001 indicated as ***.

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