Modelling gastric evacuation without meal size as a variable. A model applicable for the estimation of daily ration of cod (Gadus morhua L.) in the field

Data on gastric evacuation of cod from the International Data Base on Gastric Evacuation Experiments have been reanalysed. A general evacuation models was fitted to the data by means of non-linear regression techniques: dS/dt= - R × SB or integrated:| S(1 - B) t=S1)(1 - B) - R × (1 - B) × 1, where S=stomach content, T=time after ingestion, R and B=constants.

This model allows for various curve shapes, including linear (B=O) and exponential (B=1), and the curve shape (B) was estimated from the data. Meal size was included in the model by modifying the constant R=R′ × MD, with M=meal size in weight and D=constant. When meal size was included in the model, the resulting B values were strongly dependent on the food type and the estimated D values were negatively correlated with B: capelin, B=1.37, D= -1.16; herring, B=0.84, D= -0.57; and prawn, B=0.35, D= -0.14.

When meal size was excluded from the model, the resulting B values were closer together (capelin, 0.47: herring, 0.43; and prawn, 0.27), the loses in explained variance, however, were small (capelin, 4% herring, 1%: and prawn,