Fish Habitats
The number of species and the number of individuals in a given area depends on: local habitat (water - physical and temporal characteristics), food, and shelter. The most important axes for resource partitioning are:
Various studies have been made on resource partitioning. Different studies consider the following most important for resource partitioning are: trophic differences - 57% of studies, habitat - 32% of studies, and time - 11% of studies, but this may reflect sampling methods.
Studies of fish are biased because of historical sampling problems and research emphasis:
Freshwater represents <<0.01% of earth’s water, but contains 41% of fish species. Freshwaters are on average more productive and are structurally more complex. The local richness is affected by the size of a water body, latitude, geological history, and anthropogenic introductions.
Fish Habitats
Freshwater
Caves
Sparse fauna, some obligate (troglobites). All materials and energy supplied from outside the cave system.
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Lentic (still) - lakes and ponds - transitions in time from oligotrophic through eutrophic lakes, to ponds and, as organic material accumulates, through wetlands to forest etc. |
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Oligotrophic |
Eutrophic |
swamp |
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youthful lakes |
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deep |
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shallow |
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stratified
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fully mixed |
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seasonal turnover |
more rapid nutrient cycling |
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low productivity |
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high productivity |
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slow nutrient cycling |
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rapid nutrient cycling |
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large open water spaces |
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high oxygen |
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low oxygen |
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Greater habitat diversity for fish, macro-invertebrates etc. Larger zooplankton. |
Shallow, acidic, soft substratum, emergent vegetation beyond productive peak. |
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Fish typically strong swimmers. Filter feeding is possible. Large pelagic (salmonids) and littoral (pike) predators common. |
More diverse fish fauna. |
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Large fish common lake trout, pike, yellow perch. |
Esocidae (pike), Percidae (yellow perch), centrarchids, Ictaluridae (bullheads), Catastomidae (suckers), cyprinids. |
Umbridae (mudminnow), Ictaluridae (bullheads), Lepidosteidae (gars), Amiidae (Amia bowfin), some Centrarchidae. |
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Lotic (flowing). Channel changes along stream length and because flowing water is always eroding, stream channels change with time. Torrential: Very steep slope, >1/75 km/km, of mountain streams. Fishes are mainly herbivores feeding on diatoms and algae encrusting rocks and boulders - allochthonous inputs tend to be swept out. Holdfast organs (suckers, grapples, etc.) are common. Brook, Creek, River: middle and lower reaches |
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brook |
creek |
river |
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steep gradient <1/75 km/km >1/20 km/km |
less steep » 1/20 km/km. |
lower gradient |
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riffles and torrents |
riffles and pools |
middle reaches with more pools than riffles. Runs more common. lower reaches with meandering, stream bed and sluggish flow. |
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rocky substratum |
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sand, muck substratum |
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fast current |
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slow current |
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cold |
cool |
warm |
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high oxygen |
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low oxygen |
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Stream flow variable in magnitude and timing. |
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Stream flow lower in magnitude and variability. |
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Stochastic events important for species assembly. |
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Deterministic (biotic) processes more important in species assembly. |
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Greater retention of allochthonous inputs, with collection of material in eddies, cracks etc. Some mosses and rooted plants. Good cover for macro-invertebrates and scavengers on organic debris. |
More diverse habitats, with ripple/pool zones. Greater retention of material. |
Middle reaches have substantial allochthonous inputs, and rooted and diatom in-stream producers. Variable substratum from coarse particles to sand/silt. Lower reaches have fine substratum material, more rooted plants, and deeper stream cross-sections. |
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Fish with good locomotory and flow refuging abilities. Fish usually solitary. Eggs buried and/or adhesive. |
Lower swimming needs. More schooling species. |
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"torrential" fauna |
salmonids, cottids. |
grayling, dace, chub, darters, and suckers. |
shiners, minnows, and dace. |
suckers, bullheads and catfishes, various cyprinids, pike, centrarchids. |
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Estuaries
Very variable in terms of physical characteristics, productivity, biomass etc. depending of flushing rates of sea- and fresh-water, nutrient input rates etc.
Marine
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Benthic Animals living on or in close association with the bottom. |
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1) Splash zone |
2) Intertidal |
3) Sub-tidal |
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4) Continental Shelf |
5) Upper and Lower Shelf Zone (>200 m) |
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6) Abyssal (>3000 m) and |
7) Hadral Zones (>7000 m) |
8) Hydrothermal vents |
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Pelagic Zone |
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1) Epipelagic |
2) Mesopelagic Zone |
3) Bathypelagic |
4) Hadropelagic Zones |
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The Role of fish in their habitats
Fish are generalized carnivores consuming primary consumers and above. There is considerable debate as to how changes in fish populations affect other trophic levels, using a concept of cascading trophic dynamics.
Physical Properties of Water and Fish Habitats
Water is an alien habitat for terrestrial human animals.
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Character |
Water |
Air |
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Temperature range |
-1.86 C in SW (0 C in FW) to 45 C |
-40 to 45 C |
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Phase change to solid |
-1.86 C in SW 0 in FW ice sets lower temperature limit |
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Rate of temperature changes |
slow |
fast |
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currents/wind |
strongly displacing |
rarely problematic |
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density |
800 times greater |
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viscosity |
80 times greater |
In general, the physical properties apply which result in common problems and opportunities for aquatic animals. Although a paraphyletic group, all fish have solved common problems which results in their similarity, and the ability to readily recognize a fish as a fish.
Temperature and Phase Shifts
Temperature variation in aquatic habitats is buffered by the high thermal capacity of water, the high latent heat of evaporation, and latent heat of fusion, anomalous density changes with temperature (maximum density at 4 C) and low density of ice. The high solvent capacity allows high salt concentrations that depress the freezing point.
Density
The density of water is close to the density of body tissues, » 1070 kg.m-3. Neutral buoyancy is easily attained. Food production concentrated in lighted regions, near the water surface. Water is slow to accelerate, but high momentum once in motion and slow to stop. Hydrostatic pressure increases rapidly - about 1 atmosphere per 10 m of depth.
Viscosity
Water is about 80 times more viscous than air which adds substantially to the resistance to flow and movement.
Thermal Capacity
It is very difficult for fish to achieve a body temperature different from that of the environment.
Solvent Capacity
Water has a high solvent capacity, resulting in large variation in salinity. High solubility of CO2 makes pH regulation more difficulty, but excretion of water soluble wastes is facilitated. An exception of oxygen which is not very soluble in water.
Compressibility
Water is incompressible and sound can travel large distances and can be used as distance senses and communication. Suction feeding is common.
Transparency
Light is quickly absorbed, but this depends on wavelength. Because of turbidity, background space light with different average colors occurs in various directions.