BIOL172 Readings (intertidal fishes, extreme PH, caves)

What makes intertidal habitats physiologically challenging for fishes

Frequent fluctuations in temperature, oxygen, and salinity due to tides.

How many high and low tides occur per day in most coastal areas?

two high tides and two low tides.

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What causes the strong 'low tide' odor in mudflats and marshes?

Hydrogen sulfide released from decomposing organic material.

How does hydrogen sulfide affect fish physiology?

It interferes with hemoglobin and disrupts mitochondrial biochemistry.

Why can some intertidal fishes breathe air?

To cope with low oxygen and hydrogen sulfide in burrows or exposed mudflats.

What adaptations allow mudskippers and rockskippers to breathe air?

Gill support structures, modified buccal cavity or gut, and cutaneous respiration.

Why do many rocky intertidal fishes have eel-like bodies?

To wriggle into moist crevices for refuge during low tide.

What environmental changes occur in tidepools during summer low tides?

Rising temperature, falling oxygen, increasing salinity, and decreasing pH.

What protein helps stabilize fish biochemistry during tidepool heating>

Heat shock proteins

Why does CO₂ accumulation lower pH in tidepools?

CO₂ is more soluble than oxygen and forms carbonic acid.

What pH range do most freshwater fishes normally tolerate?

pH 6–8.

What causes naturally acidic 'blackwater' rivers?

Organic acids such as humic and fulvic acids from decaying vegetation.

What pH level eliminates many freshwater fishes, such as minnows?

Below pH 4.5

What environmental issue caused fish loss in Adirondack and Scandinavian lakes?

Acidic precipitation lowering lake pH.

What African fish survives extreme alkalinity in Lake Magadi?

Alcolapia grahami.

What are the conditions in Lake Magadi where Alcolapia grahami lives?

pH 10.5, salinity 40 ppt, temperature up to 45°C.

What determines whether freshwater fishes can cross saltwater barriers?

Their salinity tolerance (primary, secondary, peripheral categories).

What is hypersalinity?

Salt concentrations higher than seawater, often due to evaporation.

What types of fishes tolerate rapid and extreme salinity changes?

Cyprinodontoid killifishes and pupfishes.

What is the salinity of the Dead Sea and Great Salt Lake that prevents fish survival?

Over 200 ppt.

What human activity caused salinization and fish decline in the Aral Sea?

Water withdrawal for agriculture.

Why are caves considered extreme environments for fishes?

They lack light, have low productivity, and often have stable but limited resources.

What advantages do caves offer to fishes?

Few predators, few competitors, and stable climate.

What major convergence exists between cave fishes and deep-sea fishes?

Adaptations to darkness and low food availability.

What types of rock formations most commonly form caves?

Limestone formations

What term describes fishes that live permanently in caves?

Troglobitic (also hypogean, phreatic, stygobitic).

How many teleost species have colonized caves?

Over 135 species in 19 families and 10 orders.

Which major freshwater superorder dominates cave fish diversity?

Ostariophysi (characins, loaches, minnows, catfishes)

Why might enhanced hearing be useful for cave fishes?

Sound detection compensates for lack of vision in darkness

Figure takeaway: Eel-like intertidal fishes

Elongated bodies allow wriggling into moist crevices for refuge during low tide.