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Mouthbrooding

Posted by abby on March 27, 2020

Eyed eggs in a mouthbrooder (photo credit: The Fish Room).

Guest post: Gretchen Stokes, University of Florida

Mouthbrooding is when fertilized eggs are carried and incubated in the parent’s mouth. Rather sophisticated for parental care in fishes, it may have evolved from lack of nest sites, predation or habitat invasion. It occurs in more than 53 genera of fishes. Mouthbrooding can be conducted by males (paternal), females (maternal) or both. While more commonly female, parental care by males occurs in some well-known species, including snakeheads and arowana. Parental feeding is fairly or fully restricted during incubation, as swallowing or chewing could harm egg development. Brood parasitism can also occur, where a parasitic fish attacks the brooder’s eggs and leaves behind the fertilized eggs for care by the mouthbrooder (e.g. mochokid catfish eggs incubated in cichlid parent’s mouths).

Maxium sustainable yield (MSY)

Posted by abby on January 26, 2018

Optimizing fishing effort (Diagram credit: http://ib.bioninja.com.au).

Maximum sustainable yield (MSY) is a classic concept from fish population dynamics. It operates under the assumption that populations have a carrying capacity, or equilibrium size, where the the resources available match the population requirements and if individuals are removed from the population, they will be replaced (i.e., are renewable). When harvest removes a portion of the population, it lowers pressures on the population’s associated resources, such as food and habitat, allowing the remainder of the population to benefit from less competition and balance the population back to the carrying capacity. By this theory, the surplus biomass can be harvested sustainably, without long-term impacts to the population.

MSY is a commonly applied fisheries management tool, and even a guiding principle of the Magnuson-Stevens Fishery Conservation and Management Act, the primary legislation governing marine fisheries management in United States federal waters. However, it is important to note that there are many situations in which the assumptions of MSY are not met which result in overfishing and unsustainable practices.

Metamorphosis

Posted by abby on June 22, 2017

Guest post: Emily Argo

“I think you have a dead fish,” said a concerned aquarium visitor who summoned me to a nearby tank. Pointing to the tank the visitor recounted that they had been watching for a while and had not seen the fish move from it’s position on the bottom. The fish, I am happy to report, was not dead, but alive and well. The visitor had spotted a ha libut!

Halibut are flatfishes (this group also includes flounder, sole, turbot, and plaice), they begin their lives as bilaterally symmetrical larvae swimming in the water column, but eventually metamorphose over the course of a few days into a laterally compressed, pancake-like bottom dweller (and a successful sit-and-wait predator). When you think of species that metamorphose (a change in body form between life stages), fish may not be the first type of organism that comes to mind. You probably think of caterpillars and butterflies or tadpoles and frogs, but there are actually over 500 species of fish that metamorphose!

A flounder camouflaging with the bottom (photo credit: Moondigger via Wikimedia Commons [CC BY-SA 2.5]).

One of the most distinct changes that takes place during flatfish metamorphosis is the movement of one eye to the other side of the body, so both eyes are on the same side. This requires reorganization of the bones and muscles in the head of the fish and also impacts the brain and the olfactory system. Additionally, the fish will begin swimming on its side and the coloration on the top side of the body (where both eyes are) will also begin to change helping the fish camouflage with its benthic environment. All these changes are controlled in some way by the thyroid hormone, but there is still a considerable amount to learn about these mechanisms and the evolutionary benefits of these changes.

Holomictic

Posted by abby on August 12, 2016

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).

Meromictic

Posted by abby on July 15, 2016

The Black Sea is the largest meromictic lake (NASA).

Meromictic references a type of lake which is constantly stratified. The surface and bottom waters do not ever mix. In most cases, the bottom layer has very low oxygen levels, where few fish and other organisms can live, restricting them to the surface layer. Meromictic lakes are uncommon (most lakes are holomictic and turnover at least once per year) and may be formed because they are:

small and unusually deep, or
the lower layer is denser and more saline than the surface layer.

Meristics and Morphometrics

Posted by abby on October 17, 2014 Leave a Comment

Meristic and morphometric traits are used to identify fish

A meristic is a countable trait, such as number of gill rakers or number of dorsal fin spines. Morphometrics examines the size and shape using a measurable trait, such as standard length or wet weight, which can be gauged as a length, mass, angle or ratio of other measurements. Meristic traits and morphometrics are often used to classify taxa, sometimes down to the species level or sub-species level. In dichotomous keys, these counts and measurements can help identify a particular species of fish. Prior to modern genetic techniques, meristics and morphometrics were the principal foundation for fish taxonomy and systematics. Even today, meristics and morphometrics are commonly used for species identification and ground-truthing genetic analyses with phenotypic traits.

Monogamy

Posted by admin on February 19, 2014 Leave a Comment

Monogamy is a mating system where partners live and exclusively mate with only each other. These pair bonds can be transitory, just for a single breeding season, extend for several years or even a lifetime. Fish that form strong pair bonds include: American freshwater catfish, some cichlids, and many butterflyfish. The Four-Eyed Butterflyfish (Chaetodon capistratus) is one such fish that mates for life – very rare in the fish world.

Four-eye butterfly fish mate for
life

Fishionary

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