Cichlids: The Basics of Life and Development

Figure 1.Demasoni Cichlid (The Home Aquarium)

Cichlid Overview

Cichlids are a diverse group of fish from the family Cichlidae.  There are an estimated 1300 to 3000 species of cichlids. They come in a variety of shapes and sizes, ranging from 2.5 cm to 1 meter in length and can live for 4-10 years.  Cichlids originated in Africa but can be found in South America as well; most notably, they are found in Lake Malawi, Lake Tanganyika and Lake Victoria. In Lake Malawi alone, there are an estimated 1,000 different types of cichlid species (Evolutionary Biology). They prefer fresh to brackish water and usually live near the water’s surface.  Many cichlids are herbivores that feed on algae, but some are predatory and consume other small fish or insect larvaes.

Why study Cichlids?

Cichlids are great model organisms to study because they represent rapid and convergent evolutionary radiation in vertebrates. Also, there is a large variety of cichlids which makes it easier for scientists to study multiple phenotypic traits.

Cichlid Reproduction

Cichlids demonstrate four different methods of raising young:

  • Open Brooding – Laying their eggs in open spaces
  • Cave Brooding – Hiding their eggs in crevices or holes
  • Ovophile Mouthbrooding – Incubating their eggs in their mouth as soon as they are laid
  • Larvophile Mouthbrooding – Carrying their hatchlings in their mouth

The following video demonstrates cichlid mouthbrooding (around 1:10):

Additionally, cichlids can mate either monogamously or polygamously, and this is not dependent upon their brooding system. This next video shows typical cichlid mating behavior.

Brief Overview of Development

Figure 2.Nile tilapia Oreochromis niloticus (Fujimura 2007)

Stages of Embryonic Development: (Meijide and Guerrero 2000)

  • Zygote (Oocyte) – Fertilization activates cytoplasmic movements
  • 2-blastomere – Cleavage appears near animal pole and progresses towards vegetal pole
  • 4-blastomere – Second cleavage emerges
  • 8-blastomere – Cleavages occur in two separate planes
  • 64-blastomere – The sixth cleavage is the first to occur along a latitudinal plane
  • Blastomere – The onset of gastrulation

Stages of Larval Development: (Meijide and Guerrero 2000)

  • Free-swimming stage – Dorsal and anal fins appear; larvae start swimming freely during the eighth day of development; bladder is also visible due to high refractiveness.
  • Unpaired-fins stage – Dorsal and anal fin rays differentiate simultaneously; Gills are formed and the yolk is completely consumed.
  • Pre-juvenile stage – The pelvic fins, which are the last to form, have differentiated. Dorsal and anal fins are more developed.
  • Juvenile stage – Fins are complete, well-pigmented, and slightly transparent. Nostrils are observed.

Evolution of cichlid brain diversity: Click here!
The many species of cichlids have evolved to have different brain structures in the last million years. Different species have great variety in brain region sizes, which may be explained by a combination of early patterning events and timing of neurogenesis. Sylvester et al., 2010 attempts to elucidate the evolution of diverse cichlid brains in ecologically distinct fish through early patterning events.

Sexual Differentiation During Development: Click here!

Embryonic Jaw Development: Click here!

Craniofacial Diversification: Click here!

Tooth Regeneration Pathway for Cichlid: Click here!

Cichlid can regenerate their teeth throughout their lifetime. What if humans can do that? Common developmental pathway that’s found in all mammals are responsible for the teeth regeneration. So what’s allowing cichlids to regenerate their teeth but not ours?

Cichlids as Food Sources

Figure 3.Cichlid as delicious food! (Clean and Delicious)

Tilapia are a well-known type of cichlid that are commonly enjoyed as food, as they contain a substantial amount of protein.

Cichlids as Pets

Cichlids make a great addition to any fish tank, but can become very territorial and aggressive.  This video shows aggressive behavior between two cichlids in an aquarium.

However, Cichlids are also known for their parental care and elaborate courtship, as well as their ability to breed year round. If you are interested in learning more about cichlids as pets, this website would be a valuable resource.

Cichlids in Recent Research

Cichlids are constantly studied, and recently scientists have shown the ability to determine what cichlids eat from their “throat teeth”, seen in figure below.

Figure 4.The colored picture shows the contours of the teeth. The left one shows that the cichlids that eats softer food, while the one on the right eats harder food (Incisive Research Links Teeth With Diet 2012).

Learn about how different factors can affect the development of the craniofacial area! For more information about BMP and CAM and Ptch1 and how they pertain to the development of the craniofacial area, click the respective links.

References

“Incisive Research Links Teeth With Diet.” ScienceDaily. ScienceDaily, 03 Apr. 2012. Web. 27 Apr. 2012. <http://www.sciencedaily.com/releases/2012/04/120403193839.htm>.

Fujimura, K. and Okada, N. (2007), Development of the embryo, larva and early juvenile of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae). Developmental staging system. Development, Growth & Differentiation, 49: 301–324. doi: 10.1111/j.1440-169X.2007.00926.x

Meijide, F.J., and Guerrero, G.A. “Embryonic and larval development of a substrate-brooding cichlid Cichlasoma dimerus (Heckel, 1840) under laboratory conditions.” Journal of Zoology (2000) 252.4: 481-493.

Clean and Delicious. http://cleananddelicious.com/2010/01/19/post_1/.


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