The basis of food selection in flounders, Platichthys flesus (L.), in the Severn Estuary

Abstract

The factors influencing the selection of food by flounders, Platichthys Jlesus (L.), have been investigated by analysing collections made in the Severn Estuary for 1 year and the results of experiments. Flounders measuring between 6.0 and 35 cm fed heavily on the polychaete Nereis diversicolor in February and on the amphipod Gammarus salinus between February and April. Thereafter these species were replaced by the mysid Neomysis integer with the decapod Crangon iwlgaris. Hounders shorter than 6.0 cm, fed mainly on Neomysis integer regardless of month. Numerous factors were involved in the choice of the food including (1) the maximum and minimum length of prey, (2) its spatial distribution in the water column, (3) its degree of concealment, (4) its motility and ability to escape predation, ( 5 ) conditioning of the flounders for certain foods, (6) the fish's swimming speed and (7) the turbidity and temperature of the water.Although the average length of ingested prey remained unchanged as the fish grew in size, an increase in the maximum and minimum lengths was observed. The percentage of stomachs that contained no identifiable remains in flounders greater than 6.0 cm averaged 80-95 during part of the winter and 60 % in the summer and between January and March.These changes partly reflected the influence of low water temperature on the metabolic rate and availability of prey. The dry weight of the stomach contents in flounders longer than 6.0 cm was lowest in winter but high values were recorded in the spring. This latter feature was probably because the rate of feeding was greater than that of digestion. During the summer, under more normal feeding conditions, the weight of the stomach contents remained relatively low compared to other fish populations. Flounders shorter than 6.0 cm always contained more food in their stomachs on a unit weight basis than larger individuals, reflecting metabolic rate and hunting efficiency.

Estimating the food requirements of striped bass larvae Morone saxatilis: effects of light, turbidity and turbulence

“…Intuitively, turbidity should reduce the prey field of a predator by reducing light and visibility and thus the number of successful encounters. Narrowing of the prey field by turbidity has been reported for bluegill Lepomis macrochirus (Vinyard & O'Brien 1976) and flounder Platichthys flesus (Moore & Moore 1976). Swenson & Matson (1976) reported no reduction in feeding rate by larval lake herring Coregonus artedii at moderate turbidities (28 ppm), but they did note that larvae aggregated closer to the surface in turbid water.…”

Trophic niche overlap between flatfishes in a nursery area on the Portuguese coast

“…Beyst et al, 1999;Cabral 2000b;Darnaude et al, 2001), which emphasizes a generalist and an opportunistic utilization of these food resources (Lasiak and McLachlan, 1987;Beyst et al, 1999). Furthermore, niche overlap is usually minimized by differences in resource use in other niche dimensions, namely time and space (Moore and Moore, 1976;Poxton et al, 1983;Burke, 1995). Darnaud et al (2001) studied the food portioning among juvenile flatfishes in a Mediterranean coastal shallow area and found that diet overlap was low.…”

Feeding Ecology and Prey Preference of Grey Mullet, Mugil cephalus (Linnaeus, 1758) in Extensive Brackish Water Farming System

“…Fish feed opportunistically yet are often selective in their diets [5][6][7]. The main factors that determine the type of prey are feeding preference [8][9][10], availability of prey, prey mobility and its distribution in the water column, catching efficiency of the predator, water temperature and turbidity [11]. Changes in feeding habits of a fish species are a function of the interactions among several environmental factors that influence the selection of food item [12].…”