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Brown trout, Salmo trutta
Brook trout, Salvelinus fontinalis
Rainbow trout, Oncorhynchus mykiss
Hatching
Fingerling, 6 mo
Sac fry, alevin,
<6 wk
Fry, ~6 wk
Adult 2-3 yr
Fish
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
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
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.
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
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
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
____________.
Osmoregulation
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.
Osmoregulation
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
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.)
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
_____________________.
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
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.)
Temperatures in the epilimnion and
metalimnion can approach or ____________
limits,
while dissolved oxygen falls below usable
concentrations (__________) in the
hypolimnion.
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 __________________.
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
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.
Reproduction
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
 ___________
Feeding
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
Feeding
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.
Example:
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
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
swim
 they use _______________ than if they sat
on bottom
feed largely on insect larvae taken from
the bottom
Dace
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.
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
another.
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
present
 _____ 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
distribution)