Results for “od”

Mysis

Genus of mysid crustacean of which members inhabit both marine and freshwater environments. Some species are used as fish food in aquaria, and usually available frozen.

Used in 21 profiles

natural selection

Term introduced by Charles Darwin referring to the nonrandom mechanism of evolution by which certain biological traits become either more or less common in a population due to differential, environmentally-influenced reproduction. Better-adapted individuals tend to produce more offspring, thus the population evolves, and this process can result in populations that gradually become specialised to inhabit particular ecological niches and can eventually result in the emergence of new species.

nauplius

First larval stage in certain crustaceans, comprising an unsegmented body with three pairs of appendages. Important constituent of plankton and the diet of some fishes.

necrosis

Death of cells or tissue due to disease, injury, or interruption in blood supply.

Used in 12 profiles

neuromastic pitting

Severe physical condition of unconfirmed origin occurring in certain fishes which appears related to poor water quality and/or nutrition. The primary symptom is necrosis of the tissue surrounding neuromasts on both the head and body and if left unchecked the disorder can result in death. Similar to, but not analagous with, head and lateral line erosion, and does not appear to occur in nature.

Used in 1 profile

nitrates

Any salt or ester of nitric acid, and the end product of the portion of the nitrogen cycle taking place in most closed aquarium systems (the conversion of nitrates to nitrogen gas in natural systems is carried out by anaerobic microorganisms not normally present in sufficient numbers in aquaria, though this process can be induced by installation of a nitrate reactor). While nitrates are less toxic than ammonia or nitrites, they are still potentially harmful to fishes and other aquatic organisms if allowed to accumulate unchecked, and must therefore be diluted via regular water changes. Aquatic plants also help since they are able to metabolise nitrates to an extent.

Used in 20 profiles

nitrites

A salt or ester of nitrous acid. Produced in aquaria via metabolisation of ammonia by nitrifying bacteria of the genus Nitrosomonas, and toxic to fishes if present in sufficient concentrations, but in a mature system is further converted into less-harmful nitrates by other bacteria of the genus Nitrospira.

Used in 1 profile

oedema

Excess and subsequent accummulation of watery fluid in cells, tissues, or body cavities of an organism. Also spelled 'edema'.

oesophagus

Muscular tube through which food passes from mouth to stomach in vertebrates; the gullet. Also spelled 'esophagus'.

oligotrophic

Refers to bodies of water containing few nutrients and supporting little in the way of plant life. Opposite of copiotrophic.

Used in 2 profiles

oophagy

Feeding on eggs either inside or outside the mother's body

organism

An individual life form that can react to stimuli, reproduce, grow, and maintain homeostasis. There are five main groups, or kingdoms: prokaryotes, protists, fungi, plants, and animals.

Used in 127 profiles

osmoregulation

Active regulation of osmotic pressure, especially in the body of a living organism or cell, in order to prevent the body fluids from becoming too diluted or concentrated.

Ostariophysan

Fish of the superorder Ostariophysi, members of which are characterised by possession of a Weberian apparatus, i.e., the anterior four or five vertebrae are modified as a protective casing for the bony ossicles which connect the inner ear and swim bladder. The order contains such orders as Cypriniformes, Characiformes, Gymnotiformes, and Siluriformes.

outcrossing

A cross between relatively unrelated individuals; the introduction of unrelated genetic material into a breeding line. Often used to raise or maintain genetic diversity.

oviparous

Producing eggs which hatch outside the body, as in most fishes.

ovophily

Reproductive strategy whereby the eggs are laid on a solid surface where they are immediately collected and brooded in the mouth of one or both parents. Seen in some Geophagus spp., for example.

ovoviviparity

Reproductive strategy in which fertilisation occurs internally and the eggs develop inside the body of the mother until hatched, at which point live offspring are born. There is no placental connection between mother and embryo unlike in viviparous species.

ovum

Unfertilised female reproductive cell or gamete; unfertilised fish egg.

Paramecium

Genus of unicellular ciliate protozoa with a shape resembling a grain of rice, a number of species of which are cultured as live food for small fishes and fry.

Used in 117 profiles