Brown trout
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Brown trout , Salmo trutta. Brook trout , Salvelinus fontinalis. Rainbow trout , Oncorhynchus mykiss. Fry, ~6 wk. Sac fry, alevin, <6 wk. Hatching. Fingerling, 6 mo. Adult 2-3 yr. Fish. Fish dominate the ______________ in most lakes, streams, rivers and estuaries.

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Brown trout, Salmo trutta

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Brook trout, Salvelinus fontinalis

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Rainbow trout, Oncorhynchus mykiss

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Fry, ~6 wk

Sac fry, alevin, <6 wk


Fingerling, 6 mo

Adult 2-3 yr

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Fish dominate the ______________ in most lakes, streams, rivers and estuaries.

  • Their large size and _________________ greatly influence the biological structure of aquatic ecosystems.

  • Fish occupy several different levels of the aquatic food chain

    • and comprise over ____________ of the earth’s vertebrate species.

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Fish are the main ______________ product harvested from inland waters.

  • _________________ recognize that fish yield is a function of the whole-lake or stream production process.

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Fish are almost ____________, inland waters.

except in mountain lakes where it is _____________ impossible for fish to pass upstream over large waterfalls that guard the lake;

except when ______________ has completely changed the natural balance.

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Distribution and ____________ preferences inland waters.

Fish are masters of the turbulent water environment except for early _____________ life stages.

  • Fish actively _______ sites for feeding, breeding, and resting.

    The chemical and biological features of littoral habitats is directly correlated with

    • the _______ (richness) and ________ of fish species.

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Many lake fish show strong preferences for a habitat that includes

  • a diverse collection of __________ and emergent _____________.

    Important aspects of the submerged vegetation that attract fish include:

  • _______________ of the plants

  • density of the animal ____________

  • species ____________

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    High plant diversity supports a great diversity of _____________________ that are food for the fish.

    Additionally, a rich ____________ layer coating most submerged vegetation feeds small juvenile fish

    which use this vegetation as a refuge from ___________________.

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    Divisions of freshwater fish groups _____________________ that are food for the fish.

    I. Primary

    Groups with little or no ___________ for seawater;

    • lungfish, paddlefishes, pikes, minnows, catfishes, centrarchids (___________), etc.

      II. Secondary

      Groups usually ___________________

      but with enough salt tolerance so that members can enter the ocean and

    • sometimes cross ______________________

      • some gars & pikes, killifishes, live bearers (perch), cichlids.

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    Paddlefish, _____________________ that are food for the fish.Polyodon spathula

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    Northern pike, _____________________ that are food for the fish.Esox lucius

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    Warmouth (sunfish), _____________________ that are food for the fish.Lepomis gulosus

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    Mummichog (killifish), _____________________ that are food for the fish.Fundulus heteroclitus

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    Yellow perch, _____________________ that are food for the fish.Perca flavescens

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    Blue tilapia, _____________________ that are food for the fish.Tilapia aurea

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    III. _______________ _____________________ that are food for the fish.

    • Migratory between freshwater and the sea for purpose of _____________.

      ______________: diadromous fishes which spend most of their life in the sea and mature.

    • When fully grown they return to _____________________.

      ______________: diadromous fishes which spend most of their life in freshwater and go to sea as adults to breed.

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    _________________ _____________________ that are food for the fish.: regularly migrating between freshwater and the sea for purposes other than breeding.

    • Marine: spawning in marine water, with larvae and juvenile stages briefly in freshwater (______________).

    • Freshwater: spawning in fresh water with larvae and juvenile stages; ____________________ before returning to freshwater.

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    _______________ _____________________ that are food for the fish.

    Estuarine fishes that often and freely go between marine and freshwater,

    • differing from above categories which usually are capable of changing mediums________________________.

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    __________________ in freshwater fishes _____________________ that are food for the fish.

    Freshwater fishes are ________________ to their medium

    • and tend to gain water by diffusion through any ______________________.

      If uncompensated, the inward diffusion would dilute the body fluids to the point that

    • the their necessary ________________ functions could no longer be accomplished.

      • A state referred to as “________________”

  • How do they compensate?

  • Can’t waterproof (______).

  • A balance must be maintained by driving the ____________.

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    Osmoregulation _____________________ that are food for the fish.

    The task of removing water is accomplished by the kidney.

    The kidneys of freshwater fish are capable of excreting urine that is more _______________________.

    Additional contribution to ion balance by the urinary bladder:

    • ____________________ of Na+ and Cl- through the wall of the bladder.

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    Osmoregulation _____________________ that are food for the fish.

    Although the concentration of salt in urine is low,

    • the _______________ causes a significant amount of salt to be lost.

      Salts are also lost by ____________ from the body.

      Losses are balanced by __________ in food and by ________ absorption through the gills.

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    Distribution and habitat preferences _____________________ that are food for the fish.

    Temperature and _________________ also regulate fish distribution and habitat preferences.

    There is a wide variety of thermal preferences both among species and __________________.

    • Three thermal categories are:

      • cold-water

      • cool-water

      • _____________ fishes

        __________ often prefer temperatures that are several degrees warmer than adults of the same species.

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    Thermal preferences (cont.) _____________________ that are food for the fish.

    These different thermal preferences act to

    _________________with different thermal tolerances during summer stratification.

    Thereby, the thermal preferences can either enhance or reduce _______________ for other resources

    depending on whether they __________similar species in more limited areas

    or separate ____________________.

    Although in winter, many species move to deeper water,

    ____________________ due to the much lower levels of activity and feeding associated with reduced _____________________.

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    Wading shorebirds from the west coast of North America _____________________ that are food for the fish.

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    Temperature and oxygen gradients can interact to _____________________ that are food for the fish.

    • exclude fish from all or a fraction of a water body.


    • are a common problem in ________ eutrophic

    • warm water reservoirs and some natural lakes.

      The hypolimnion initially becomes _________ in summer

      and the ____________________ gradually rises through the season.

      Meanwhile, the thermocline is descending (_________________ as surface layer warms).

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    Oxygen-temperature squeeze (cont.) _____________________ that are food for the fish.

    Temperatures in the epilimnion and metalimnion can approach or ____________ limits,

    while dissolved oxygen falls below usable concentrations (__________) in the hypolimnion.

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    Habitat preferences (cont.) _____________________ that are food for the fish.

    Fish that are vulnerable to predation use a combination of

    • ____________________ to minimize their exposure to _____________ predators.

  • Silversides, Menidia sp., migrate from cover in littoral areas to feed in the _________________ epilimnion offshore at dawn

    • but return to shorelines in the morning before they are ___________.

  • They could fill their stomachs if they remained offshore,

    • but they minimize daylight exposure to offshore __________________.

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    Menidia sp _____________________ that are food for the fish.., silversides

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    Similarly, the pelagic juvenile _______________, _____________________ that are food for the fish.Oncorhynchus nerka,

    • stay in ______________ water during the day,

      • and ascend to feed for a short period in the zooplankton-rich epilimnion at _____ and dawn.

    • They ascend when light levels are just sufficient to __________________

      • but dark enough to minimize the probability of detection by _____________.

    • In contrast, the older, less vulnerable kokanee feed _________ in the lighted epilimnion.

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    Reproduction _____________________ that are food for the fish.

    Reproductive strategies consist of reproductive traits that enable fish to leave some ________.

    • Reproductive traits reflect responses to environmental fluctuations.

      Traits that vary, include:

    • ___________ according to size and age

    • reproductive _____

    • size of ________ (large eggs---larger larvae---

      • mouth size, swimming capacity, sensory abilities increase with size

        reproductive behavior, __________ timing,

        ___________, the number of times spawning occurs in the life of the female (parity)

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    Age category terminology _____________________ that are food for the fish.

    1. Age groups represent the number of years a fish ____________

    • age group 0 = fish in ___________ of life

    • age group 1 = fish in second year of life.

      2. ____________: fish born in 1997 are members of the 1997 year class.

      Fry and fingerling; variously defined, often with different meanings to different people, should not be used unless specifically defined.

    • ____: the time between hatching and the time at which they reach 25 mm in length

    • ____________: fishes between 25 mm and the length at age 1 (Piper et al., 1982).

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    Age category terminology/Aging _____________________ that are food for the fish.

    _________ fishes: newly hatched.

    • Aging methods:

      • scale annuli, circuli, focus

      • ___________

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    Feeding _____________________ that are food for the fish.

    Fish are often the only important large aquatic predators

    and results of their __________________

    • Example: one small fish can eat hundreds more zooplankton than the largest predatory zooplankter.

      Effect of fish on zooplankton __________________

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    Feeding may be divided among _____________________ that are food for the fish.

    1. pelagic fish, which feed in open water

    _______________(shad, herring, whitefish, minnows) or piscivorous (mosquito fish, white bass), may also eat ________________

    • some feed at surface (trout, sunfish)

      2. littoral, feed at ___________

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    3. _____________________ that are food for the fish.benthic, feed on the bottom of lakes and streams.

    Benthic and littoral feeding is more generalized and can include:

    • grazing on aquatic plants (___________)

    • ingestion of bottom debris (_____________),

      • covered with ______________, protozoans, small insect larvae, and worms

    • ingestion of benthic invertebrates

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    Feeding _____________________ that are food for the fish.

    In _______________,

    • some fish eat _____________________

    • some pluck insect larvae and crustaceans from the _____________

    • some feed on _________ in pools

    • some seize ____________ adult insects

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    Resource _______________ _____________________ that are food for the fish.

    Some fish are ____________,

    while others are very specialized in their selection of food.

    This resource partitioning means that the fish eat only ______________ of the available food

    and thus avoid too much _________________ with others.

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    Example: _____________________ that are food for the fish.

    Two species of trout: _______ trout (Salvelus fontinalis) and _________ trout (Oncorhynchus mykiss)

    • brook feed mainly on bottom, taking chironomid and _________________

    • rainbow, feed near the surface on ____________ organisms in summer

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    Resource partitioning _____________________ that are food for the fish.

    Another example: In streams,

    • the largest, most aggressive carnivores (such as trout)

      • pick off the ________________

        • above and below __________, or near banks of submerged vegetation.

    • smaller fish, (such as sculpin and dace)

      • catch benthic invertebrates in the _______________ of the riffles

      • suckers ________________ at the bottom of the pools.

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    Mottled sculpin, _____________________ that are food for the fish.Cottus bairdi

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    ___________ in flowing waters _____________________ that are food for the fish.

    ____________ or negative, (positive)

    • _____________ (yes or no)

    • negative buoyancy is advantageous for fish that ________________

      • as _________ tends to hold it in place.

    • many stream and river fish that live and feed on the bottom,

      • _______ or have reduced swimbladders.

    • A fish with neutral buoyancy has no __________ in water.

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    Energy ____________: resting on bottom versus continuous swimming against current (_________)

    Dace have a swimbladder and continuously swim

    • they use _______________ than if they sat on bottom

      • feed largely on insect larvae taken from the bottom

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    Dace swimming against current (_________)

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    Perhaps they catch more ________ by swimming above the bottom

    • than they could if they crept about on the bottom.

  • In this case ___________ swimming increases a fish’s success in finding food

    • and ___________ the extra metabolic cost of swimming.

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    Many fish that live in fast ________________ are negatively bouyant

    • and they possess _________.

      ____ may be expanded to form a relatively small sucker around the mouth (Gyrinocheilus)

      The entire ______________ of the body acts as a sucker (Gastromyzon) both are members of Cyprinidae

  • A fish attached by a sucker depends on friction to ____________________,

    • an extra _________ force is applied by the sucker, increasing the friction.

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    Roanoke hog sucker, bouyantHypentelium roanokense

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    Most _____________ fish feed on algae which encrust the rocks.

    They collect a large quantity of food from one rock before making a ________________ for another.

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    Stream ecology/fish ___________ rocks.

    Distribution of fish is impacted by

    • water temperature

    • ____________________ and discharge

    • level of _______________

    • substrate type, sediment load

    • depth,

    • food _____________/abundance

    • etc....later

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    Stream ecology/fish zonation rocks.

    Stream zones have been named for the _______________________ or associations found there.

    • These zones or associations have mainly _______ application.

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    Measurement: ______________________ rocks.

    Fishery studies involve:

    • collection & ______________ of the species present

    • _____ determination

    • growth ______

    • habitat __________

    • ___________ structure

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    Collecting/Sampling ______________ rocks.

    Nylon nets: __________, gill nets,

    • _______ nets or _____ nets (for collection of live migrating fish in streams and small rivers)

      • fixed-trap nets with __________ throats which the fish enter but have difficulty exiting.

    • __________ trawls

    • _______________ (streams and shallow regions of lakes)

    • Rotenone (blocks ____________________)

    • _______________ assessment (estimates population abundance, temporal and spatial distribution)