General Information about Fish
(both cartilaginous and boney fish)
 (material taken from North Carolina Aquarium at Manteo and
information acquired from my Vertebrate Zoology class)

The density of water makes it difficult to move about, but fish have over come this obstacle. One adaptation that bony fish possess is the swim bladder. The swim bladder is an air compartment which the fish regulates to influence its buoyancy. Oxygen gas is the principle gas found in the swim bladder; nitrogen and carbon dioxide also moves in reflexively. In the front of the swim bladder there is a specialized valve which allows for gas to pass into the compartment. Gas leaves the bladder through an oval body in the back of the swim bladder. There are contracture, and relaxer muscles that surround the swim bladder which regulates the movement of gas throughout the system.

Sharks and other elasmobranches don’t have a swim bladder to regulate their buoyancy. These fish have an extremely large liver which stores fatty acids, and oils which help maintain buoyancy. The liver can take up approximately 5 to 25 percent of the shark’s weight, and roughly 90 percent of the shark’s internal space.

Both cartilaginous fish and bony fish have fins. fins provides the fish with control over its movements by directing thrust, supplying lift and even acting as brakes; to move in water a fish must control its pitch, yaw, and roll. The Caudal fin helps provide thrust, and helps support the fish’s direction. The Pectoral fins act mostly as rudders and hydroplanes to control yaw and pitch. Pelvic fins influence pitch, and Dorsal/anal fins control roll.

Pitch is when the fish moves up, or down in the water column.

Yaw is when the fish moves to the left, or right.

Roll is when the fish rotates on its stomach.

Drag is a force in the opposite direction of movement.

To minimize Drag fish have a streamline torpedo shaped body, and they may secrete a mucus substance on their skin.

Sharks and other elasmobranches have dermal denticles on their skin which are like teeth which also help to minimize drag.

One main difference between bony fish and cartilaginous fish is their skeleton. The skeleton of cartilaginous fish is composed of cartilage, and the skeleton of bony fish is comprised of bone. Since cartilaginous fish don’t have a swim bladder it is advantageous for them to have a skeleton that is comprised of cartilage which is lighter than bone.

Another obstacle that fish face by living in the water is the availability of oxygen. Fish have a relatively simple circulatory system; the fish heart is comprised of 2 chambers, because the heart pumps blood in one direction. The blood enters the heart through a vein and exits through an artery on its way to the gills. Once the oxygen deprived blood reaches the gills oxygen can defuse from the water to the blood. Next the blood which contains oxygen leaves the gills in arteries, and gets shuttled to the rest of the body. Gills are composed of a gill arch (which gives the gill support), gill filaments (always paired), and secondary lamellae (where gas exchange occurs). Oxygen deprived blood flows into the gill filaments in the opposite direction as the water; this set up is known as a counter current system. The counter current exchange system gives fish 80-90% effectiveness in acquiring oxygen out of the water.

Cartilaginous fish have 5 gill slits, where as boney fish have only 1 gill slit.

Fish don’t chew their food; some fish will eat their prey whole, and others will bight off pieces of their prey.

If the fish do chew their prey they would increase the risk of damaging their gills. Fish have gill rakes that prevent large particles from entering the gill cavity.

Reproduction is different between boney fish, and cartilaginous fish.

Cartilaginous fish reproduce internally where as boney fish reproduce externally.

There are three different embryonic developments that cartilaginous fish can undergo.

Oviparous is when the cartilaginous fish releases the developing embryo in a hard shell casing into the water.

Ovoviviparous embryos are protected by a thin membrane, and are retained within the mother’s body. The embryos hatch internally, and then are released into the water. Theoretically the embryos nutrients comes from the yolk within its shell membrane; in some species the lining of the uterus secretes fluids that are rich in nutrients which gets absorbed by the embryo.

In other species the first embryo to hatch will eat other developing embryos, and or other smaller hatched embryos.

Viviparous embryos develop internally, and receive its nutrients through a yoke like placenta. The uterus lining secretes a nutrient rich substance which baths the developing embryo, and this rich substance also gets absorbed by the yoke placenta.

Once cartilaginous embryos hatch they are well equipped to survive on their own.

Boney fish reproduce externally.

The female releases lots of eggs into the water, and males will then release sperm into the water in hopes that his sperm will fertilize the eggs.

In some species the females will dig crevasses in the sand, and then release their eggs. In other species the females will release their eggs directly into the water column.

The embryos develop in a soft membrane casing. They get their nutrients from a yoke; even after they hatch through the membrane their yoke will continue to provide the embryo with nutrients.

 

 The Effect of an Exotic Fish Species to
the Atlantic Ocean: Pterois volitans

Common names include:

Lionfish, Red Lionfish, Zebra Fish, Turkey Fish, Butterfly Cod, Peacock Lionfish, Firefish, and Scorpion Volitans.  

Biological Classification:

 

The Lionfish is an invasive species to the Atlantic waters, but is native to the Indo-Pacific region. How the Lionfish were first introduced into the Atlantic Ocean is still unknown, but there are two speculations on how they became established. The first hypothesis is that the lionfish were intentionally released by aquarium owners, and the second hypothesis is that hurricane Andrew flooded an aquarium which led to the Lionfish’s escape into various water ways.

The lionfish is characterized by its red, maroon, and white bands which cover its head and body. Fleshy tentacles surround the head, and mouth. The lionfish has elegant fan like pectoral fins, and 10 dorsal rays. Among the dorsal rays the lionfish has 13 long, separated dorsal spines. The lionfish has 7 anal rays, and 3 spines that lie between the fins. The spines that lie between the lionfish fins are venomous. When the lionfish reaches maturity it is approximately 18 inches long, and juveniles can be as small as 1 inch.

The Lionfish is an exotic species which means that it was transported by human activities from its native region into a region where it does not occur naturally. Once the lionfish established residence in the Atlantic Ocean it became an invasive species because it does not have any natural predators to control its population.  Since the Lionfish does not have any natural predators, its presence can disrupt the normal balance of the ecosystem.

Sunken ships and coral reefs provide the lionfish with an optimal habitat. The lionfish’s diet consists primarily of shrimp, other small crustaceans, and fish.  The crevasses and other niches found in coral reefs support ample food of this type thus giving the lionfish a perfect environment in which to survive.  Lionfish are active hunters; these predators lie in wait, and when an appetizing specimen comes along they ambush the unsuspecting prey. Their bright colorations are thought to be used to deter other predators from preying on them. The lionfish’s venomous spines are believed to be a defense mechanism rather than a hunting strategy. They may also use their spines in a demonstration technique to ward off other males during the mating season.

Little is known on the lionfish mating behavior. The female lionfish releases a mucus sack of eggs, and fertilization is achieved externally. The egg sack floats for a while and over time the mucous membrane will deteriorate releasing the eggs into the water column. Since little is known about the growth rate of juvenile lionfish scientists use the growth rate of Scorpaena (which is in the same family as the lionfish) to estimate the growth rate of the lionfish. The growth rate of Scorpaena is approximately 0.3 mm per day; for 30 to 40 days. With this estimate it is believed that juvenile lionfish grow approximately 12 mm in about a month then sink down into the benthic region of the water column. The life span and sexual maturity of the lionfish is still unknown.

 

Currently lionfish are not listed as endangered, or threatened in their native range however, the increase in pollution to the ocean may negatively affect the lionfish’s primary food sources. The declines in the lionfish prey may intern have a negative effect on its population. Economically lionfish are very popular in the fishing trade; in the U.S. lionfish are high in demand for privet aquarium owners.  They are harvested in their native range, and sold as pets to dealers. Over harvesting May also in tern lead to a decline in the lionfish’s population in its native range.

 

Recommendations to Prevent the Introduction of Exotic Species into Various Waterways

1.  Don't leave live bait in waterways - this could affect native species that live there.

2.  Make sure bottoms of boats and boots are clean before introducing into waterway - this can prevent the introduction of various species.

3.  Do research before researching pets to be sure you can handle them as they grow and develop.

4.  Help educate friends and family members on the effects of exotic species.

5.  Help out local officials in capturing and relocating exotic species.

 

References

NOAA news Online. Researchers Plan August Hunt for Invasive Lionfish off Carolina Coast. July 16, 2004. http://www.noaanews.noaa.gov/stories2004/s2264.htm     [accessed 2007 October 2]

Hare, J.A., and P. E. Whitfield. 2003. An integrated assessment of the introduction of lionfish (Pterois volitans/miles complex) to the western Atlantic Ocean. NOAA Technical Memorandum NOS NCCOS 2. 21 pp.

Whitney, D. Introduced species Summary Project: Lionfish.19 Feb. 2003. http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/Pterois_volitans.html [accessed 2007 October 2]

* All photos are from NOAA's website: http://www.noaa.gov

 

This webpage was designed by Jessica Kremidas, October 2007.