Influence of Body Weight and Food Density on Kinetics of Ammonia Excretion by the Brine Shrimp Artemia franciscana

This study was undertaken to quantify the relationships between the rate of ammonia excretion by brine shrimp and dry weight (body size) and food density. Measurements of the rate of ammonia excretion of the brine shrimp were made at 25 C in darkness. Under these conditions, the excretion rate of ammonium‐nitrogen can be generalized as a function of body weight and food ( Nannochloropsis sp.) density. The relationship between the body weight (W) and excretion rate of ammonium nitrogen (E N ) is expressed as E N =α W γ , where α is the metabolic level. The parameter α is dependent on ration, such that α=α o ±α r where α o = metabolic level in starvation and α r = the metabolic level which increased with feeding or changed with the food density. In experiments in which the animal starved, the equation above becomes E N =α o W γ , and the values of α and γ were 0.22 and 0.93, respectively. The rate of ammonium excretion rose from 5.42 × 10 −4 to 2.28 × 10 −1 μg N/animal/h as dry weight measured from 1.57 × 10 −3 − 1.04 mg dry weight per animal. Next, it is convenient to express α r as α r =α fmax = (1 − 10 −kc ), where α fmax is the maximum rate of α f at saturated level of food density, C is the mean cell density, and k is a constant defining the rate of change of the metabolic rate with cell density. Therefore, the rate of ammonia excretion by brine shrimp could be expressed as E N =α o [1 − a(l − 10 −kC )]W γ , and a =α fmax /α o . The values of the kinetics parameters obtained from experiments where shrimp were fed were a = 2.3 and k = 0.15×10 −7 . Consequently, the maximum rate of ammonia excretion at a saturated food density is equivalent to 3.3 times the rate of animals that are not fed.