| Popis: |
In salmon culture facilities, the balance between oxygen consumption and supply is critical and so a model to predict oxygen levels in rearing facilities has been constructed. The oxygen concentration at the outflow of a rearing pond (Cf) was expressed as a function of oxygen concentration of the inflow stream (Ci), loading rate (Lr=biomass of fish per unit water flow), reaeration rate within the pond (k) and oxygen consumption of the fish (Ro). Of these variables, Ro is the most complex and difficult to model. To model Ro, oxygen consumption rates for both juvenile and adult salmon were measured under typical fish culture conditions. Average daily Ro values for juveniles had a mean of 245.5 mg kg−1 h−1 (s.d.=67.4, n=129) and ranged between 83 mg kg−1 h−1 for starved fish, to over 400 mg kg−1 h−1 for fed fish. Peak daily Ro values often were 20% higher than average daily values (mean peakto-average ratio=1.2048, s.d.=0.075, n=79). Ro values for nonfeeding adult salmon varied between 35 mg kg−1 h−1 for fish holding quietly in low velocity ponds to over 300 mg kg−1 h−1 for actively migrating and spawning adults. Measured Ro values for juveniles were related to ration level, temperature and fish weight using a variety of empirical models. It was found that the product of ration and temperature accounted for 65% of the variation in measured values. The most accurate predictor of Ro was the Response Surface Analysis (RSA) model of Schnute and McKinnell (1984). The maximum allowable load rate, or carrying capacity of the water supply, occurs when Cf is at the lowest acceptable level. These limits to Lr define the water flow requirements for juvenile rearing. Using oxygen criteria of Davis (1975) to define acceptable oxygen levels and Ro values predicted from the RSA model, carrying capacity under a variety of conditions was calculated. The limitations of this model also are discussed; it is recognized that other water quality factors or disease considerations may further limit the carrying capacity of a water supply. |
