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Holomictic

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Dimictic lakes commonly have turnover in spring and fall with stratification in summer and winter (Nature Times).

Dimictic lakes commonly have turnover in spring and fall with stratification in summer and winter (Nature Times).

Holomictic references the most common type of lake which turns over at least once per year (as opposed to meromictic lakes which are constantly stratified).  This mixing is an important process for maintaining fish and aquatic communities by distributing nutrients and oxygen throughout the lake before stratification occurs again.  There are four categories of holomictic lakes:

  • Oligomictic: mixing is irregular,
  • Monomictic: turnover occurs once a year (most common in polar areas)
  • Dimictic: turnover occurs twice a year (most common in temperate areas), and
  • Polymictic: frequent turnover (most common in tropical areas).

Homocercal

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The rose fish has an even-lobed homocercal tail.

The Rose Fish has an even-lobed homocercal tail.

A homocercal tail is a caudal fin composed of two lobes of equal proportion.  Homocercal tails are the most common caudal fin type in fish but can come in many symmetrical shapes.  A homocercal tail is contrasted with a heterocercal tail which has unequal lobes.

Heterocercal

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The heterocercal tail of a shark is a caudal fin with unequal lobes.

The heterocercal tail of a shark is a caudal fin with unequal lobes.

A heterocercal tail is a caudal fin composed of two asymmetrical lobes.  Often, such as the case in many sharks, the vertebral column passes through the upper lobe, making it the larger of the two lobes.  A heterocercal tail is contrasted with a homocercal tail which has equal lobes.

Habitat

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Fish out of water! Mudskippers have a very unique habitat

Fish out of water! Mudskippers have a very unique habitat

Habitat, is simply, the location where a fish lives.  It applies to any and all life stages.  It is where a fish survives, feeds, grows, and reproduces.  The habitat of a fish depends on the species, from wetlands, to rivers, to coral reefs, to lakes, and more.

Most fish do require well-oxygenated water.  But, there are a few exceptions in which fish have evolved to tolerate low oxygen conditions or even low water conditions.  Mudskippers (family Gobiidae; subfamily Oxudercinae), for example, are amphibious fish that are adapted to intertidal zones.  Some live in mud flat habitat that is only covered in water at high tides.

Habitat is where it’s at!

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