Satiation-dependent, intra-cohort variations in prey size selection of young roach ( Rutilus rutilus )

Predators exert strong regulating forces on lower trophic levels through predation. As most fish are visual foragers, visual conditions in the water may alter the strength of this regulation. We evaluated effects of turbidity and humic water on foraging efficiency and prey-size selectivity in Northern pike (Esox lucius) feeding on roach (Rutilus rutilus). Encounter rates decreased in both turbid and humic water but were not counteracted by increased searching activity. Capture success was unaffected by turbidity but was nonlinearly affected by humic water by being high in clear and highly humic water but low in less humic water. In highly humic water, the visual range approached pike’s strike distance and, together with its cryptic colours, pike may have initiated its attack before the prey detected it, limiting the possibility for prey evasive manoeuvres. Prey-size selectivity towards small prey in clear water disappeared in turbid water but was maintained in humic water. Owing to its optical properties, turbidity degrades the quality of the visual information more through scattering than humic water does through absorption. We show that the effect of visual degradation on foraging depends on the cause of visual degradation, which has not previously been acknowledged in the visual foraging literature.

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Consumption and prey size selection of the nematode Caenorhabditis elegans by different juvenile stages of freshwater fish

Nematology ◽

10.1163/15685411-00002793 ◽

2014 ◽

Vol 16 (6) ◽

pp. 631-641 ◽

Cited By ~ 15

Author(s):

Sebastian Weber ◽

Walter Traunspurger

Keyword(s):

Caenorhabditis Elegans ◽

Freshwater Fish ◽

Common Carp ◽

Prey Size ◽

Size Classes ◽

Size Selection ◽

Ninespine Stickleback ◽

Nematode Abundance ◽

Juvenile Stages ◽

Selection Of

Meiofauna, and nematodes in particular, play an essential role in the diet of certain juvenile freshwater fish. However, the specific consumption and prey size selection of fishes on nematodes is largely unrecognised. In this study, the effects of different juvenile stages of widely distributed common European freshwater fish, gudgeon (Gobio gobio), roach (Rutilus rutilus), ninespine stickleback (Pungitius pungitius), and two strains of common carp (Cyprinus carpio (scaled) and C. carpio (mirror)), on abundances of the nematode Caenorhabditis elegans were investigated in controlled laboratory experiments with a known number of prey. Gudgeon, carp (scaled), and carp (mirror) consumed significant amounts of nematodes, whereas the roach and ninespine stickleback did not. Both strains of common carp reduced nematode abundance dependent on the size of the fish, with smaller fish causing a greater reduction than medium-size or large fish, although fish of all sizes fed significantly on nematodes of all size classes (<0.5, 0.5-1.0 and >1.0 mm). While the gudgeon also reduced nematode abundance dependent on the size of the fish, with increasing body length there was a dietary shift towards larger nematode size classes (0.5-1.0 and >1.0 mm). Morphometric analysis of the branchial basket indicated that the mesh width of gudgeon and both strains of common carp, but not of roach and ninespine stickleback, is suitable for feeding on specific size classes of nematodes. Together, the results showed that nematodes are used as a food source for different juvenile stages of certain species of freshwater fish.

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Prey size selection in invasive (Hemigrapsus sanguineus and H. takanoi) compared with native (Carcinus maenas) marine crabs

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315419000985 ◽

2019 ◽

Vol 100 (1) ◽

pp. 73-77

Author(s):

Mark M. Bouwmeester ◽

Andreas M. Waser ◽

Jaap van der Meer ◽

David W. Thieltges

Keyword(s):

Resource Competition ◽

Size Range ◽

Prey Size ◽

Carcinus Maenas ◽

Hemigrapsus Sanguineus ◽

Crab Species ◽

Size Classes ◽

Size Selection ◽

Size Preference ◽

Selection Of

AbstractIntroductions of predators can have strong effects on native ecosystems and knowledge of the prey size selection of invasive predators is pivotal to understand their impact on native prey and intraguild competitors. Here, we investigated the prey size selection of two invasive crabs (Hemigrapsus sanguineus and Hemigrapsus takanoi) recently invading European coasts and compared them with native shore crabs (Carcinus maenas) which are known to feed on similar prey species. In laboratory experiments, we offered different size classes of native blue mussels (Mytilus edulis) to different size classes of the crab species in an effort to identify the respective prey size preferences and potential overlap in prey size range of native and invasive crabs. In all three species, the preferred prey size increased with crab size reflecting general predator–prey size relationships. Prey size preference did not differ among the crab species, i.e. crabs showed similar mussel size preference in relation to carapace width. Given that additional morphological measurements showed that both of the invasive crab species have much larger claws relative to their body size compared with the native species, this finding was surprising and may relate to differential claw morphologies or structural strength. These results suggest that the invasive crabs exert predation pressure on the same size classes of native mussels as the native crabs, with potential effects on mussel population dynamics due to the high densities of the invaders. In addition, the overlap in prey size range is likely to result in resource competition between invasive and native crabs.

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