As the prey thickens: rainbow trout select prey based upon width not length

Drift-feeding fish are typically considered size-selective predators. Yet, few studies have explicitly tested which aspect of prey “size” best explains size selection by drift-foraging fish. Here, we develop a Bayesian discrete choice model to evaluate how attributes of both prey and predator simultaneously influence size-selective foraging. We apply the model to a large dataset of paired invertebrate drift (n = 784) and rainbow trout (Oncorhynchus mykiss) diets (n = 1028). We characterized prey “size” using six metrics (length, width, area, hemispherical area, volume, mass) and used pseudo-R2 to determine which metric best explained observed prey selection across seven taxa. We found that rainbow trout are positively size-selective, they are selecting prey based upon differences in prey width, and size-selectivity increases with fish length. Rainbow trout demonstrated strong selection for the adult and pupae stages of aquatic insects relative to their larval stages. Our study provides strong empirical evidence for size-selective foraging in rainbow trout and demonstrates prey selection is based primarily upon width, not length or area as has been widely reported.

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Changes in Habitat Use and Feeding Chronology of Juvenile Rainbow Trout (Oncorhynchus mykiss) in Fall and the Onset of Winter in Silver Creek, Idaho

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f93-237 ◽

1993 ◽

Vol 50 (10) ◽

pp. 2119-2128 ◽

Cited By ~ 64

Author(s):

Michael D. Riehle ◽

J. S. Griffith

Keyword(s):

Rainbow Trout ◽

Habitat Use ◽

Oncorhynchus Mykiss ◽

Density Distribution ◽

Stomach Contents ◽

Early Morning ◽

Invertebrate Drift ◽

Juvenile Rainbow Trout ◽

Rainbow Trout Oncorhynchus Mykiss

We assessed changes in density, distribution, and microhabitat of age-0 rainbow trout (Oncorhynchus mykiss) in Silver Creek, a partially spring-fed stream, by periodic snorkeling in August 1987 through January 1988. We examined trout stomach contents and invertebrate drift samples in diel collections in August, September, October, and January to test if the period of feeding shifted from daytime to nighttime, concurrent with a transition to day concealment. In late September, fish aggregated briefly during the day and then began to conceal themselves in macrophyte beds, undercut banks, and submerged sedges and grasses along streambanks as temperature dropped below 8 °C in early October. Fish emerged from concealment at night, and numbers of trout visible were greatest 30–60 min after sunset and about 30 min before sunrise. Periods of peak feeding changed from afternoon and evening in August and September, when fish were day active, to mainly at night in October after the initiation of day concealment. Trout did not feed upon abundant chironomids in the daytime drift in October. In January, fish fed at 1–4 °C on mayflies, and stomachs were fullest in the early morning. Observations suggest that Silver Creek trout experienced a metabolic deficit that began in September.

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Prey size and availability limits maximum size of rainbow trout in a large tailwater: insights from a drift-foraging bioenergetics model

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2015-0268 ◽

2016 ◽

Vol 73 (5) ◽

pp. 759-772 ◽

Cited By ~ 13

Author(s):

Michael J. Dodrill ◽

Charles B. Yackulic ◽

Theodore A. Kennedy ◽

John W. Hayes

Keyword(s):

Rainbow Trout ◽

Prey Size ◽

Prey Availability ◽

Maximum Size ◽

Large Prey ◽

Bioenergetics Model ◽

Prey Biomass ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Temperature Regimes ◽

Prey Resources

The cold and clear water conditions present below many large dams create ideal conditions for the development of economically important salmonid fisheries. Many of these tailwater fisheries have experienced declines in the abundance and condition of large trout species, yet the causes of these declines remain uncertain. Here, we develop, assess, and apply a drift-foraging bioenergetics model to identify the factors limiting rainbow trout (Oncorhynchus mykiss) growth in a large tailwater. We explored the relative importance of temperature, prey quantity, and prey size by constructing scenarios where these variables, both singly and in combination, were altered. Predicted growth matched empirical mass-at-age estimates, particularly for younger ages, demonstrating that the model accurately describes how current temperature and prey conditions interact to determine rainbow trout growth. Modeling scenarios that artificially inflated prey size and abundance demonstrate that rainbow trout growth is limited by the scarcity of large prey items and overall prey availability. For example, shifting 10% of the prey biomass to the 13 mm (large) length class, without increasing overall prey biomass, increased lifetime maximum mass of rainbow trout by 88%. Additionally, warmer temperatures resulted in lower predicted growth at current and lower levels of prey availability; however, growth was similar across all temperatures at higher levels of prey availability. Climate change will likely alter flow and temperature regimes in large rivers with corresponding changes to invertebrate prey resources used by fish. Broader application of drift-foraging bioenergetics models to build a mechanistic understanding of how changes to habitat conditions and prey resources affect growth of salmonids will benefit management of tailwater fisheries.

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Rainbow trout (Oncorhynchus mykiss, walbaum 1792) leucocyte interactions with the larval stages of Diphyllobothrium dendriticum, nitzsch, 1824 (Cestoda, pseudophyllidea)

Developmental & Comparative Immunology ◽

10.1016/0145-305x(91)90306-j ◽

1991 ◽

Vol 15 ◽

pp. S88

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Larval Stages ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Diphyllobothrium Dendriticum

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Diel Feeding Chronology and Diet Selection of Rainbow Trout (Oncorhynchus mykiss) in the Henry's Fork of the Snake River, Idaho

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f90-022 ◽

1990 ◽

Vol 47 (1) ◽

pp. 199-209 ◽

Cited By ~ 81

Author(s):

T. R. Angradi ◽

J. S. Griffith

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Stomach Content ◽

Decision Rules ◽

Stomach Contents ◽

Live Weight ◽

Invertebrate Drift ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Terrestrial Insects ◽

Prey Items

Concurrent rainbow trout (Oncorhynchus mykiss) stomach contents and invertebrate drift samples were collected during three 24-h periods in summer 1987. Feeding was discontinuous through the day on all dates. Mean stomach content weight was minimal after 0400 MST and sharply increased between 1000 and 1200 MST on all three dates. Feeding apparently did not occur after twilight. Mean stomach content weight was correlated with water temperature on two dates and was never correlated with invertebrate drift density for non-age-0 trout. Daily ration (wet weight) was 7% of live weight for non-age-0 trout and 21% for age-0 trout. Trichoptera, Ephemeroptera, and Diptera were most important in the diet; terrestrial insects and aquatic vertebrates were rare. The degree of selectivity varied through 24 h and the interpretation depended on the method of analysis used. Occurrence of low-drift cased Trichoptera larvae in stomachs was correlated with amount of filamentous algae ingested, indicating a degree of epibenthic foraging, although no diel pattern could be reliably discerned. Mean length of prey items in stomachs was larger that the drift in 83% of the samples. Our findings support experimentally derived decision rules-of-thumb for foraging trout: select larger prey items, select vulnerable prey, and relax selectivity when hungry.

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Diel Food Selection by Two Sizes of Rainbow Trout (Salmo gairdneri) in an Experimental Stream

Journal of the Fisheries Research Board of Canada ◽

10.1139/f78-158 ◽

1978 ◽

Vol 35 (7) ◽

pp. 971-975 ◽

Cited By ~ 45

Author(s):

Peter A. Bisson

Keyword(s):

Rainbow Trout ◽

Prey Size ◽

Feeding Activity ◽

Food Selection ◽

Salmo Gairdneri ◽

Invertebrate Drift ◽

Small Fish ◽

Drift Density ◽

Experimental Stream ◽

Selection Of

The food selected by small (~ 3 g) and large (~ 45 g) hatchery rainbow trout (Salmo gairdneri), studied over a 28-h period, showed that the fish fed selectively, but often on different prey organisms. Feeding activity was highest during daylight hours but was only loosely associated with increases in invertebrate drift density. The majority of large trout exploited adult chironomids on the surface, whereas small trout fed primarily on midwater drift. At night when drift densities were low the limited feeding that took place apparently shifted to bottom foraging. Prey size was the most important factor affecting vulnerability to predation at all hours. Both large and small fish rarely consumed invertebrates < 2 mm long. Selection of larger individuals among certain prey taxa occurred, and in two important groups (Trichoptera and Chironomidae) large trout ate significantly larger prey than did small trout. By being size selective, the trout lost the opportunity to exploit smaller organisms, particularly Collembola, which constituted the bulk of the total drift. Key words: diel habits, drift, predation, rainbow trout, size selection

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Direct and indirect effects of sediment pulse duration on stream invertebrate assemblages and rainbow trout (Oncorhynchus mykiss) growth and survival

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f01-160 ◽

2001 ◽

Vol 58 (11) ◽

pp. 2213-2221 ◽

Cited By ~ 82

Author(s):

E Al Shaw ◽

John S Richardson

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Pulse Duration ◽

Indirect Effects ◽

Benthic Invertebrate ◽

Fine Sediment ◽

Sediment Supply ◽

Invertebrate Drift ◽

Total Abundance ◽

Rainbow Trout Oncorhynchus Mykiss

Elevated concentrations of inorganic sediment supply in streams may impair many biological functions. However, the contribution of exposure duration to the observed impacts has not been previously considered. We evaluated the effects of sediment pulse duration using 14 streamside flow-through experimental channels, each of which contained a naturally colonised invertebrate assemblage and 10 rainbow trout (Oncorhynchus mykiss) fry. Channels were exposed to fine sediment pulses of constant concentration but varied pulse duration (ranging from 0 to 6 h) every second day over 19 days. Total abundance of benthic invertebrate and family richness declined as sediment pulse duration increased. Invertebrate drift total abundance increased as pulse duration increased; however, family richness of drift decreased. Trout length and mass gain over the 19-day period was negatively correlated with pulse duration. Path analysis suggests that the direct effects of fine sediment on trout (impaired vision leading to reduced prey capture success and (or) increased metabolic costs from physiological stress) are more important to trout growth than indirect effects (decreased drift and benthic invertebrate richness and drift abundance).

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