The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon

Abstract

1. Most animals are active by day or by night, but not both; juvenile salmonids are unusual in that they switch from being predominantly diurnal for most of the year to being nocturnal in winter. They are visual foragers, and adaptations for high visual acuity at daytime light intensities are generally incompatible with sensitive night vision. Here we test whether juvenile Atlantic Salmon Salmo salar are able to maintain their efficiency of prey capture when switching between diurnal and nocturnal foraging. 2. By testing the ability of the fish to acquire drifting food items under a range of manipulated light intensities, we show that the foraging efficiency of juvenile salmon is high at light intensities down to those equivalent to dawn or dusk, but drops markedly at lower levels of illumination: even under the best night condition (full moon and clear sky), the feeding efficiency is only 35% of their diurnal efficiency, and fish will usually be feeding at less than 10% (whenever the moon is not full, skies are overcast or when in the shade of bankside trees). Fish were unable to feed on drifting prey when in complete darkness. 3. The ability of juvenile salmon to detect prey under different light intensities is similar to that of other planktivorous or drift‐feeding species of fish; they thus appear to have no special adaptations for nocturnal foraging. 4. While winter drift abundance is slightly higher by night than by day, the difference is not enough to compensate for the loss in foraging efficiency. We suggest that juvenile salmon can nonetheless switch to nocturnal foraging in winter because their food requirements are low, many individuals adopting a strategy in which intake is suppressed to the minimum that ensures survival.

Seasonal feeding selectivity of brown trout Salmo trutta in five groundwater-dominated streams

“…This pattern was also evident in other winter studies of brown trout diet in southeastern Minnesota (Anderson et al 2016;French 2014;French et al 2014), and for salmonids in other regions where nocturnal benthic feeding in winter was attributed to lower capture efficiency of drift because of reduced light from ice cover, elevated turbidity, lower drift rates, and avoidance of predators (Tippets and Moyle 1978;Cunjak and Power 1986;Jørgensen and Jobling 1992;Heggenes et al 1993;Fraser and Metcalfe 1997;Johansen et al 2010).…”

Combining Radio and PIT-Telemetry to Study the Large and Fine-Scale Movements of Stocked and Wild Brown Trout (Salmo trutta L.) in a Northeastern Stream, Portugal

“…These fishes displayed an activity pattern more intense during day-light hours, namely during the dawn period. Normally, hatchery-reared trout are more active than wild fish (McLaren, 1979) and the higher mobility pattern showed during day-light hours in this study was, probably, related to the rearing environment (feeding habits in the hatchery) and the increasing ability of fish to detect food as light intensity increases (Fraser & Metcalfe, 1997). Furthermore, these results are according to the exploratory experiments made over two weeks in the previous year and confirmed the lack of a capacity to define a territory and a non-cost-effective behaviour, also detected by other authors (Bachman, 1984).…”

“…Stocked trout were shown to be more active during the day periods than during the night period in the Baceiro stream and can be related to the feeding habits acquired in the fishfarms. Brown trout is a visual feeder and the foraging efficiency decreases as light intensity declines (Fraser & Metcalfe, 1997;Klemetsen, 2003), but nocturnal (Clapp et al, 1990) and crepuscular (Bunnel et al, 1998) feeding patterns were also reported. However, the tendency of stocked trout in the Baceiro stream must be confirmed in complete (24 h) diel cycles.…”

Re-Evaluation of the Effect of Daily and Within-Day Mixed Feeding Schedules of Varying Dietary Protein Content on the Growth Performance of Nile Tilapia Fry Using Constant Ingredient Composition

“…25) by Kjeldahl method, fat (solvent extraction with petroleum ether, BP 40-60 Co 129 for 10-12 h), ash (oven incineration at 550°C), while nitrogen free extract was calculated by difference. Gross energy was calculated using conversion factors of 9.5, 5.6 and 4.2 Kcal g -1 for fat, protein, and carbohydrate, respectively [37].…”

“…This hypothesis was tested in many cultured species including Nile tilapia [9,[15][16][17], common carp [18][19][20][21], Catla Catla [22], Channa striata [23] and silver carp [24]. Fish exhibit a distinct diel pattern in feeding [25,26]. Previous studies reported that fish have different patterns in their feeding rhythms: photophase is the preferable feeding time for specific species and they called diurnal feeders such as goldfish, rainbow trout, sea bass and green black founder [27][28][29][30][31][32], while, other species consider scotophase is the preferable feeding time such as African catfish and Atlantic salmon [33,34].…”