Download BIOL213 Lect 7 Fish in Rivers

BIOL213 Lect 7 Fish in Rivers
By Dr Rick Leah
It is recommended that you follow-up subjects from the lecture by further reading. These
notes are intended only as a memory prompt – The course website is being developed to
provide additional information but is NOT a substitute for reading.
Major Fish Groups
You should be aware of the major evolutionary groups of fish and where common
British species fit into the scheme – particularly:
Actinopterygii
Ostariophysi
Fish anatomy and Biology
Understanding the morphology of a fish is fundamental to our understanding of its ecological
role within a FW ecosystem
Fish types
Introduction to main components of the British Fish fauna - refer to Website / Maitland
Composite fish diagram and measurements (Both)
Many of the features seen here are used to identify and understand the functional morphology
of fish
Body form and shape
Standard Length - rest as a % of this therefore compare between species
 BD to FL ratio (Fineness ratio) and where the greatest BD occurs along the body tells us
about streamlining
Range from <2 to 10+
Good stream lining 3 to 7
4.5 is optimal only in streamlined fish that are continuous swimmers (tuna)
Max BD 1/3 way along body
 Relative ED - visual awareness
 Relative HL - food intake
 Relative CPD and Caudal fin - speed and acceleration (muscle and surface area)
Triangle of optima
Different body shapes are adapted for different types of swimming which are related to
different ecological niches.
Fins structure and position
Rays
 The rays are simple (anterior) or branched (posterior) and the simple can be spiny
 Different numbers and types of rays = different species
 2 simple then 10 branched in the dorsal fin is written 2/10 if spiny then II/10
 Spiny more advanced and allows delicate and controlled movement
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Fins are paddles (undulate) and brakes
Position allows manouverability
Pectoral higher up and pelvic forward allows excellent movement but speed acceleration
can be lost
Change with species and age of fish
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Head and Mouth morphology
 Mouth position top (oblique / bleak), middle (terminal / grass carp) and bottom (inferior
/ barbel)
 Teeth, bony plates, pharyngeal teeth, filter feeders
 Give us clues but fish very adaptive can often feed in a number of ways on different food
types
Gills and Rakers
Gill rakers
 Oxygen gathering organ large surface area to extract O2
 Gill arch number varies between species
 Filament structure short long number of vary
 Depends on O2 requirment of fish and habitat best suited to
 Gill rakers can be close or wide apart act as filters planktivores closer
 Size and width can change as fish become mature
Scales
2 Scales
 Various types but most common are simple cycloid and advanced ctenoid
 Ctenii on outer edge interact with water boundary layer help stabilise fish but add drag at
low speeds
 Lateral line pore bearing scales
 Sensory system more is better
 Species specific identify
 So type of scale and number on lateral line again tell us about where and how fish are
adapted
So morphology tells us a lot about how fish are linked to their ecological niche and show
some of the factors that determine the final fish community structure.
The British Fish Fauna
British fish communities/ associations /guilds. Example riverine fish include:
 Salmon
 Trout
 Stone loach
 Bullhead
 Grayling
 Barbel
 Chub
 Dace
 Minnow
 Eels
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Factors that determine and influence the distribution of fish in rivers and lakes (Abiotic
and Biotic)
Trophic Categories
 For a fish to grow and survive in an aquatic habitat needs to acquire food
 Fish can be separated into trophic categories
Herbivores
Planktivores
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algae and macrophyte material
phytoplankton
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Carnivores
Zooplanktivores
Benthivores
Piscivores
Scavengers
Detritivores
Omnivores
range in size from micro to meso carnivores
animal plankton
bottom living invertebrates
fish - either different species or cannibalistic
dead organisms
organic material (often decomposing)
the majority of species esp. in temperate waters
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Some of these trophic feeders better suited for different parts of the aquatic environment
Rivers tend not to have much plankton especially in the upper reaches
Deep lakes with steep sides tend not to have a lot of macrophytes
Shallow lakes ideal for all of them
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Fish occupy similar parts of the ecosystem either daily, seasonally or different stages of
their life cycles.
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Young perch are planktivores but older ones typically eat macro-invertebrates
Although resources are partitioned competition for resources occurs
Roach are good omnivores and when smaller fish are eating the phytoplankton they often
switch to feeding on macrophytes (plants)
Or bream have highly protusible mouths and are better able to feed on the quicker (often
larger) zooplankton so roach often get the smaller ones
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A very complex and interwoven ecosystem
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Take into account their movements (daily and lifecycle) and habitat choice when trying to
understand the community
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Especially when sampling for representative fish species, size and number.
Influence of Abiotic (physical) Environment on fishes from rivers and streams
On a macro-level many things influence fish presence (More Abiotic but affects Biotic too)
Tributaries and catchment
 Width and depth of river increases downstream
 Tributaries come together
 More water discharged from an increasing catchment area
Reservoirs
 Artificial impoundments stop movements of materials downstream
 Food, nutrients and essential ions therefore fish downstream can be less
 Stop fish moving upstream therefore species above may not be what is expected
Urban and industrial areas
 Towns, cities and villages are built next to or around rivers
 The inputs from these and effects downstream can change the fish community in a major
way
 Not get what might be expected if environmental conditions not correct
 Will discuss pollution effects in greater detail in the next lecture
Tidal effect
 Many species cannot tolerate saline therefore it is a real physical barrier
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General River Profile
Gradient
Changes over distance
 Steep Rhithron to gentle Potamon
 Consequences for substrata
 Large boulders upstream to small particle downstream
Flow of water
 Fish species present dependent on the flow conditions
 2 main zones Erosional and Depositional
Erosional zone
 Upper reaches
 Shallow water so not much volume for fish to inhabit
 Flow is torrential and turbulent as gradient high
 Large rocks present adds more turbulence
 Oxygen high and altitude = cool temperature (helps high O2)
Types of fish
 Most fish benthic
 Bullhead and stone loach
 Flat ventral surface
 Mouth inferior helps bottom feeding
 Paired fins adapted to cling to rocks and jam in crevices (Goby pelvic fins fused to form
disc has weak adhesive properties)
 No swim bladder (buoyancy organ)
Pools and riffles
 Further downstream similar O2 and temperature
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Low energy areas within rivers (River morphology and flow regime)
 Rivers flow at different speeds across the profile – fast in middle / slow edges and river
bed
 Fish utilise this to reduce energy expenditure and to swim upstream
 More extreme cases of waterfalls
Waterfall
 Salmonids utilise the kinetic energy within the water to help them move up these
Eddies behind rocks
 Fish such as Salmonids can hold their station in turbulent upstream areas
 Metabolically still expensive but little competition for food or spawning sites
Eddies and side channels
 These have slower water
 Less energy required to stay
 Therefore often favoured by fish
General river profile
 Remember though that upstream little vegetation or plankton so typically carnivores
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Abiotic influence on the biotic
Also remember that more light as clear water and little vegetation so smaller eyes
Relates back to morphology and suitable habitat
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Less turbulent and slower flow so more fish species can swim against the flow
Pools and rivers are distinct habitats so different fish utilise the different habitats
Greater volume of water therefore larger habitat to occupy
Fish density
Filamentous algae and plants can start to grow
More invertebrates as well
Overall greater biological diversity including fish
However storms up river can increase flow rates so fish species all able to swim at
prolonged or burst activity to find shelter in eddies
Depositional Zone
Gradient gentle
 Water loses some of its energy as widens and deepens
 Also greater volume so greater fish density
 Flow transforms from turbulent to laminar
 Get quiet waters with some shallow and rapid areas
 Deposition of suspended organic material increases
 Therefore plants more stable
 More food for invertebrates
 Thus more fish species and increased competition
Low Oxygen
 Levels of oxygen fluctuate more due to increased respiration and decomposition
 Higher temperature also lower DO
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Typical fish shown
Further downstream
 Water meanders slowly and is much deeper
 More plants along sides but can be too deep
 Water drag makes water flow completely laminar
 Slow water means can heat up
 Oxygen even lower as water heated and decomposition of deposited material
 Substrate is soft and muddy
 More specialised invertebrates
 Food range therefore narrows (plant and inverts)
 Fish need more adaptations Carp and Bream have protusible mouths and suck up
sediment for inverts
 Lower fish diversity
 Similarities between Potamon and lakes (next lecture)
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