Archive for January, 2019


TAXONOMY
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii (ray-finned fishes)
Order: Characiformes (Characins)
Family: Characidae (Characins)

Genus/species: Astyanax mexicanus 

 

GENERAL CHARACTERISTICS: The head is notable for the absence of eyes. Young are born with functioning eyes which become completely enclosed in tissue as fish grows. The lack of sight is compensated by a highly developed lateral line that detects vibrations and changes in the water. The fish is without pigmentation and is plain pink with a silver sheen. They live in schools and grow to about 12 cm or 4.72 inches.

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DISTRIBUTION/HABITAT: Texas, New Mexico, and eastern and central Mexico in freshwater pools within dark caves.

DIET IN THE WILD: A keen sense of smell and electrolocation aid in finding food. Blind cave fish are omnivores and feed on animal and plant remains that wash into the caves and on bat droppings from cave ceilings. Much of their time is spent searching for food; they are able to store four times more energy as fat than their surface-dwelling relatives, allowing them to deal with irregular food supplies.

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REMARKS: Two forms of A. mexicanus (eyed and eyeless) being members of the same species, are closely related and can interbreed.

The loss of eye tissue in the blind cavefish, which occurs within a few days of their development, happens through epigenetic silencing of eye-related genes, according to a study led by the National Institutes of Health. Epigenetic regulation is a process where genes are turned off or on, typically in a reversible or temporary manner. This mechanism differs from genetic mutations, which are permanent changes in the DNA code. The study appears in Nature Ecology & Evolution.

References

California Academy of Sciences Steinhart Aquarium Water planet Senses Cluster,  Dr Bart Sheperd

Ron’s flickr  http://www.flickr.com/photos/cas_docents/sets/72157608608528651/with/2999116145/

Ron’s WordPress Shortlink  http://wp.me/p1DZ4b-11I

Read more at: phys.org/news/2018-05-eye-loss-cavefish.html#jCp

NIH phys.org/news/2018-05-eye-loss-cavefish.html

TAXONOMY
Kingdom: Animal
Phylum: Chordate
Class: Actinoptery
Order: Osteoglossiformes
Family: Mormyridae  (Elephantfishes)
Genus/species: Gnathonemus petersii

GENERAL CHARACTERISTICS: The snout is its most unique feature. It is not actually a nose, but an extension of the mouth that is covered in electroreceptors that capture information from the weak electric field the fish generates. Receptors, which cover much of the body are used to navigate, avoid predators, and find food and mates in the turbid waters of its habitat.

Maximum length: 35.0 cm (13 in)

DISTRIBUTION/HABITAT: G. petersii are found in African fresh waters often murky.

DIET IN THE WILD: They feed mostly at night on worms and insects probably aided by electro-sensory inputs.

IUCN: Least Concern

Elephantnose fish have the largest brain of any fish their size with a brain size to body weight ratio higher than a human’s.
They have been used by water departments in the U.S. and Germany to test the quality of drinking water. When the quality of the water declines, the amount of electrical pulses released increases.

They are depicted in ancient Egyptian tombs dating from 2500 BC

References

California Academy of Sciences Steinhart Aquarium, Senses Cluster 2019

Ron’s flickr https://www.flickr.com/photos/cas_docents/4734491953/in/album-72157675574079744/

Frontiers of Zoology https://frontiersinzoology.biomedcentral.com/articles/10.1186/1742-9994-6-21

fishbase. www.fishbase.se/summary/Gnathonemus-petersii.html

www.deepdyve.com/lp/wiley/fish-monitors-and-the-role-of-e…

Ron’s WordPress Shortlink https://wp.me/p1DZ4b-1Zw

TAXONOMY
Phylum: Chordate
Class: Actinopterygii
Order: Scorpaeniformes
Family: Rhamphocottidae, Grunt Sculpins
Genus/species: Rhamphocottus richardsoni

GENERAL CHARACTERISTICS: Short stocky body. Most of body covered with prickles. Head and body colored yellowish-beige, streaked with dark brown; ventral surface creamy yellow to pale red. Base of caudal fin is bright red. Fin rays mostly reddish.
Their large heads represent over half of their total body length—and feature a long, tapered snout, two bony ridges on top, and small cirri on the upper lip. Instead of scales, their bodies are covered with small plates containing numerous tiny spines.

Length 5-7.6 cm (2-3 in).

DISTRIBUTION/HABITAT: Pacific Ocean, Japan north to Alaska, south to Santa Monica Bay, California. Habitat: Rocky and sandy substrates, tide pools. Grunt sculpins use the barnacles’ shells as protection and egg-laying sites. In this position, the shape of its head resembles the former resident of the shell.

Intertidal to 165 m. (540 ft)

DIET IN THE WILD: Crustaceans. Young consume zooplankton, invertebrate and fish larvae

LONGEVITY: about four years.

REPRODUCTION: Observations in captivity show that during spawning season the female chases the male until he is trapped in a rocky cavern. She keeps him captive until her eggs are laid; fertilization is external. After the eggs are fertilized, the female leaves the male to guard the nest. She may return occasionally to take a shift protecting the eggs. When it’s time for the eggs to hatch, whichever parent is guarding them (male or female) takes the eggs into its mouth, leaves the nest and literally spits the eggs out—breaking the eggs open. The newly hatched larvae then swim away to begin their lives.

REMARKS: Produces grunt-like sounds when removed from water, thus the common name. Eyes operate independently.
Like most sculpins, rarely swims freely in the water column; instead usually “walks” with a hopping motion over the substrate by use of its large, fan-like pectoral fins. Frequently observed taking shelter in empty shells, including those of the giant barnacle, Balanus nubilis, as well as in cans and bottles.

They move by crawling on the tips of their finger-like pectoral fins in a series of twitchy hops, jerks and jumps.

They make a wheezing-grunting sound when removed from the water, hence the name, grunt sculpin.

References

California Academy of Sciences Steinhart Aquarium, Water Planet Locomotion 2018

Ron’s Flickr https://www.flickr.com/photos/cas_docents/15896092713/in/album-72157662278273245/

Ron’s WordPress Shortlink https://fishoncomputer.wordpress.com/wp-admin/post-new.php

Seattle Aquarium https://www.seattleaquarium.org/animals/grunt-sculpin

Aquarium of the Pacific http://www.aquariumofpacific.org/onlinelearningcenter/species/grunt_sculpin/

TAXONOMY
Phylum: Mollusca
Class: Gastropoda,
Order: Nudibranchia (sea slugs)
Family Tethydidae

Genus/ species: Melibe leonina

YouTube VIDEO  http://youtu.be/Xe2bM2kKm-U

GENERAL CHARACTERISTICS: Color a translucent gray, greenish-gray, or yellowish-gray, with opaque brown hepatic diverticula. Melibe leonina has 4-6 pairs of large, leaflike or paddlelike cerata in two rows down its dorsum and a large oral hood with two rows of filiform tentacles around its margin.

Length up to 102 mm long (4 in), 25 mm (1 in) wide, and 51 mm (2 in) across the expanded oral hood.

DISTRIBUTION/HABITAT: West coast of North America from Alaska to Baja California in eelgrass beds, kelp (especially Macrocystis) beds, harbors. When swimming it is usually upside-down, and undulates back and forth.

DIET:  M. leonina feeds on Copepods, amphipods, and ostracods, as well as small post-larval mollusks. They firmly attache itself to a kelp blade and then sweeps its raised hood downward or to the side. When food lands on the lower surface of the hood, the melibe sweeps together the two sides of the hood, and its fringing tentacles lock in the prey. The hood contracts to force the captured food into the M. leonine’s mouth.

REPRODUCTION and DEVELOPMENT:  M. leonine are hermaphrodites (they have both male and female sexual organs), and fertilization is internal. The animal can lay as many as 30,000 eggs, which are enclosed in a long, gelatinous ribbon.

REMARKS:  Noxious secretions of the melibe smell like watermelon, according to aquarists. They are gregarious animals and probably use it to keep together as well as for defense.  Most predators avoid the noxious secretions of nudibranchs; but the kelp crab is an exception. 

This species has been used for neurological research.

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References

California Academy of Sciences, Steinhart Aquarium, Water is Life 2019

Ron’s WordPress Shortlink wp.me/p1DZ4b-fW

Ron’s flickr www.flickr.com/photos/cas_docents/sets/72157608597736188/

Monterey Bay Aquarium www.montereybayaquarium.org/animal-guide/invertebrates/me…

EOL eol.org/pages/454874/details

 

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