The effect of body size on food consumption, absorption efficiency, respiration, and ammonia excretion by the inland silverside, Menidia beryllina (Cope) (Osteichthyes: Atherinidae)

The inland silverside, Menidia beryllina (Cope), is an annual zooplanktivore that occurs in estuarine and freshwater habitats along the Atlantic and Gulf of Mexico coasts and drainages of the United States. Experiments were conducted at 25 ± 1°C to quantify the relationship between mean dry weight (WD) and rates of energy gain from food consumption (C), and energy losses as a result of respiration (R) and ammonia excretion (E) during routine activity and feeding by groups of fish. The absorption efficiency of ingested food energy (A) was also quantified. Rates of C, E, and R increased with WD by factors (b in the equation y = aWD b) equal to 0.462, 0.667, and 0.784, respectively. Mean (±SE) rates of energy loss during feeding were 1.6 ± 0.1 (R) and 3.4 ± 0.6 (E) times greater than those for unfed fish. Absorption efficiency was independent of WD and estimated to be 89% of C. From these measurements, the surplus energy available for growth and activity (G) and growth efficiency (K1) were estimated. Over the range in sizes of juveniles and adults (5-500 mg WD), predicted G and K1 values decreased from 7.42 to 0.20 J mg fish-1 day-1 and 63 to 21%, respectively. Measured and predicted bioenergetic parameters are discussed within an ecological context for a northern population of this species.