Temperature-dependent digestion handling time in juvenile cod and possible consequences for prey choice

Abstract

The paper combines experimental work with modelling. The aim was to estimate the temperature-dependent digestion handling time, which is defined as the time taken to digest the whole prey or the whole stomach contents, and to examine potential consequences of prey digestibility on prey choice. A surface-dependent digestion model that reflects the geometric shape of a piscivore prey was applied to experimental data representing the weight of prey remaining undigested at various points in time from the time at which the prey was first ingested. The fish used were juvenile cod fed different meal sizes of two-spotted goby Gobjusculus flavescens Fabricius at 4 temperatures. It is assumed that prey digestion is a surface process in which digestive enzymes attack progressively deeper into a prey of known size and shape so that the average digestion rate would be proportional to prey radus. This process IS characterized by the digestion velocity d, (cm h-') and the digestion handling time. d, was estimated for various meal sizes and temperatures. Next, these estlrnates were used to obtain a standardized temperature-dependent function: d, = dso[e~h34'"0)T], of which the standardized digestion velocity estimate at O°C, d, = 0.0026 cm h-' The d, relation expresses the digestion velocity over a 10-fold meal size increase for a temperature range within natural seasonal variation for the cod. The digestion velocity d, was constant for a 10-fold difference in meal size within the temperature range. However, the digestion handling time increased with increasing meal size, but decreased with increasing temperature. It was demonstrated that predictions from a modified prey choice model which incorporates the effect of digestion differ from predictions from classical models which do not account for prey digestion.

Water Temperature and Prey Size Effects on the Rate of Digestion of Larval and Early Juvenile Fish

“…Thus, our results suggest a 95% probability of confirming the presence of larval fish prey during stomach content analyses at 1-2 h postingestion, depending on water temperature and larval fish size; this probability decreased to 50% at 2-4 h post- FIGURE 2.-Adjusted least-squares mean degree of digestion for larval prey fish fed to predatory bluegills that were held at constant cool (mean 6 SD, 10 6 18C) or warm (19 6 18C) water temperatures. Our results also are consistent with expectations and previous conclusions regarding the effects of prey size, temperature, and time on digestion (Windell et al 1976;Folkvord 1993;Knutsen and Salvanes 1999;Vinagre et al 2007;Yamamoto et al 2007). Larger larval fish were expected to be digested more slowly because as fish grow, (1) surface area per unit mass decreases, resulting in reduced exposure to digestive enzymes, and (2) scale and hard-structure development progresses, providing greater resistance to breakdown.…”

Sub-populations of coastal cod with different behaviour and life-history strategies

“…Similarly, differences in food consumption between high-and low-latitude populations of Atlantic silverside (Menida menida) was explained by adaptation of high-latitude populations to a shorter growth season than southern populations (Present & Conover 1992). Another abiotic environmental factor that constraints growth is low ambient temperature (Jobling 2002) due to temperature influences on enzymatic processes such as digestion (Knutsen & Salvanes 1999), and thus assimilation and growth. Selection for individuals capable of fast growth under low temperature or other environmentally limiting circumstances might therefore also be favoured at high latitudes.…”

A dynamic fish digestion–assimilation model: oxygen consumption and ammonia excretion in response to feeding

“…48. In particular, Fänge and Grove (1979, p 205) and Boehlert and Yoklavich (1983) both show that gastric evacuation is faster at a higher temperature; Boehlert and Yoklavich (1983) also show that maintenance respiration increases with temperature; and Knutsen and Salvanes (1999) indicate that digestion rate increases with temperature. Based on the current model, a higher OC plateau is expected at higher temperatures, not due to a larger capacity of the digestive tract, but due to an increased digestion rate (a).…”