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Brown trout, Salmo trutta
Brook trout, Salvelinus fontinalis
Rainbow trout, Oncorhynchus mykiss
Fingerling, 6 mo
Sac fry, alevin,
<6 wk
Fry, ~6 wk
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
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
 the _______ (richness) and ________
of fish species.
Many lake fish show strong
preferences for a habitat that
 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
I. Primary
Groups with little or no ___________ for
 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.
Paddlefish, Polyodon spathula
Northern pike, Esox lucius
Warmouth (sunfish), Lepomis gulosus
Mummichog (killifish), Fundulus heteroclitus
Yellow perch, Perca flavescens
Blue tilapia, Tilapia aurea
III. _______________
 Migratory between freshwater and the sea
for purpose of _____________.
______________: diadromous fishes which
spend most of their life in the sea and
 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
Freshwater fishes are ________________ to their
 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 Clthrough 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
Temperature and _________________ also
regulate fish distribution and habitat
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
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
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
Wading shorebirds from the
west coast of North America
Temperature and oxygen gradients can interact to
 exclude fish from all or a fraction of a water
 are a common problem in ________ eutrophic
 warm water reservoirs and some natural
The hypolimnion initially becomes _________ in
and the ____________________ gradually rises
through the season.
Meanwhile, the thermocline is descending
(_________________ as surface layer warms).
Oxygen-temperature squeeze (cont.)
Temperatures in the epilimnion and
metalimnion can approach or ____________
while dissolved oxygen falls below usable
concentrations (__________) in the
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
 but they minimize daylight exposure to
offshore __________________.
Menidia sp., silversides
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
 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
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
_________ 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
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
 brook feed mainly on bottom, taking
chironomid and _________________
 rainbow, feed near the surface on ____________
organisms in summer
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.
Mottled sculpin, Cottus bairdi
___________ 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
 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
 In this case ___________ swimming increases a
fish’s success in finding food
 and ___________ the extra metabolic cost of
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
 A fish attached by a sucker depends on
friction to ____________________,
 an extra _________ force is applied by the
sucker, increasing the friction.
Roanoke hog sucker, Hypentelium roanokense
Most _____________ fish feed on algae which
encrust the rocks.
They collect a large quantity of food from one
rock before making a ________________ for
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 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
 _____ determination
 growth ______
 habitat __________
 ___________ structure
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