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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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Fry, ~6 wk

Sac fry, alevin, <6 wk


Fingerling, 6 mo

Adult 2-3 yr


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.
Fish are the main ______________ product harvested from inland waters.
  • _________________ recognize that fish yield is a function of the whole-lake or stream production process.
Fish are almost ____________,

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.

distribution and preferences
Distribution and ____________ preferences

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.
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 ____________
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 ___________________.

divisions of freshwater fish groups
Divisions of freshwater fish groups

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.
III. _______________
  • 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.

_________________: 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.

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

  • differing from above categories which usually are capable of changing mediums________________________.
in freshwater fishes
__________________ in freshwater fishes

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 ____________.

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.

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.

distribution and habitat preferences
Distribution and habitat preferences

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.

thermal preferences cont
Thermal preferences (cont.)

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 _____________________.

Temperature and oxygen gradients can interact to
  • 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).

oxygen temperature squeeze cont
Oxygen-temperature squeeze (cont.)

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

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

habitat preferences cont
Habitat preferences (cont.)

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 __________________.
Similarly, the pelagic juvenile _______________, 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.

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)

age category terminology
Age category terminology

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).
age category terminology aging
Age category terminology/Aging

_________ fishes: newly hatched.

  • Aging methods:
    • scale annuli, circuli, focus
    • ___________

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 __________________

Feeding may be divided among

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 ___________

3. 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

In _______________,

  • some fish eat _____________________
  • some pluck insect larvae and crustaceans from the _____________
  • some feed on _________ in pools
  • some seize ____________ adult insects
Resource _______________

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.


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
resource partitioning
Resource partitioning

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.
in flowing waters
___________ in flowing waters

____________ 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.
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
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.
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.
Most _____________ fish feed on algae which encrust the rocks.

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

stream ecology fish
Stream ecology/fish ___________

Distribution of fish is impacted by

  • water temperature
  • ____________________ and discharge
  • level of _______________
  • substrate type, sediment load
  • depth,
  • food _____________/abundance
  • etc....later
stream ecology fish zonation
Stream ecology/fish zonation

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

  • These zones or associations have mainly _______ application.
Measurement: ______________________

Fishery studies involve:

  • collection & ______________ of the species present
  • _____ determination
  • growth ______
  • habitat __________
  • ___________ structure
collecting sampling
Collecting/Sampling ______________

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)