Okay, der er vist opstået nogle problemer med modellen. Kan ikke umiddelbart bestemme Km under de nuværende betingelser (som beskrevet i artiklen). Hvis jeg køre modellen over fire timer, kan jeg ikke se knækket selvom jeg bruger en Km fra 1 til 1200. Kan ikke se hvor modellen går galt.
Hvis jeg køre modellen over 15 timer, får jeg noget der ligner fig. 3. Det giver mig Km på 40
Endvidere, så fungere væksten ikke.
Model
Model of a system from Fry and Hart (2007) with an aquarium containing goldfish and a water flow.
When determining the km value the variables were kept specific values, as described below. Afterwards the water temperature and other variables were changes to values more resembling North Africa. These setting are described below, but can also be adjusted using the sliders below the info box.
The model contains factors such as fish growth, temperature, Km, water flow and aquarium size. The weight-specific fish respiration is determined by water temperature and Km value.
As indicated by the name, 'Growth on/off', the slider turns fish growth on and off. A value of 0 turns off the growth and 1 turns on the growth.
Determining Km value
The Km was determined from trail and error to fit figure 3 in Fry and Hart (2007). The variables were set as following:
Temp.: 15 degrees celcius
Aquarium volume: 4 liters
Fish stock: 0.076 kg (20 x 3.8 g)
Run time: 4 hrs
Flow: 0 L/hr (off)
Fish growth: 0 (off)
Fish growth
Wet fish biomass consists of 45% carbon, 10% nitrogen, 1.5% phosphor, 1.5% minerals and 43% water. As one mole of carbon weighs 12 grams, is is associated with 26.7 grams of fish biomass. This means that for every one mole of carbon the fish stock assimilate, 26.7 grams biomass is gained.
For determining the growth rate it is assumed that for every mole of oxygen is respired, one mole of carbon is assimilated. Thus the growth is:
Growth in kg = [Fish respiration] * 2.64*10^(-8)
The initial fish stock was 0.076 kg corresponding to 20 goldfish with an average mass of 3.8 grams as described in Fry and Hart (2007).