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The shape of fish

Posted on: August 24, 2012

Fish body shape comparison graphic

Fish body shapes give clues to how it moves through the water.

Did you know that the shape of a fish depicts where in the ocean it lives? Some fish are built for speed, others for manoeuvrability and some are built to travel long distances.

Demersal, or bottom-dwelling species, such as flounder and wobbegongs, are generally flat in shape. They do not have to be streamlined as they don’t tend to swim continuously, and being quite flat in shape allows them to stay close to the bottom and close to their food source.

Fish that live around reef areas (e.g. butterfly fish) have deep, flat bodies and are highly agile so they can move around easily.  Long, slender fish (e.g. moray eels) have the ability to hide under rocks and amongst coral.

Slow-moving fish with rounded bodies tend to have spines or armour plating, and many have poisonous flesh (e.g. blowfish) as forms of protection.  Fish with more elongated bodies (e.g. Australian herring) have the ability to swim relatively fast for long periods of time and thus don’t have the need for any special body protection.

The internal anatomy of a fish may also play a role in the fish’s survival.  Pelagic, or open water, fish such as tailor have a small swim bladder.  The swim bladder is an organ that the fish controls the amount of oxygen in, that enables the fish to control its ability to ‘float’ and ‘sink’ in the water column. Demersal species such as Western Australian dhufish have relatively large swim bladders to cope with large changes in pressure.  If you were to conduct a fish dissection with your students (see the Marine WATERs Lesson Plan: Dissect a Fish), the swim bladder, assuming it hasn’t been perforated, will be the air filled sac under the intestine. You can be assured it is quite safe to ‘pop’, in fact it is a bit of an anticlimax – no noise, no smell, no gooey stuff spurting out.

To find out more about fish shapes and how they aid a fish’s survival, check out the Marine WATERs Poster: Fish ‘Fiziks’.

Masters of Adaptation

Posted on: August 17, 2012

Mangrove roots half in water with foreground water and some leaves above.

Mangroves in the Broome region.

Are you studying adaptations with your students?  Have you considered mangroves as a focal point?

About 11,000 kilometres (or over a million hectares) of Australia’s coastline is covered with mangrove forests making them one of Australia’s most geographically widespread ecosystems. This area represents the third largest area of mangroves in the world.  

In Western Australia, mangroves occur naturally in most coastal areas from Shark Bay northwards. There are also small mangrove communities at the Abrolhos Islands, and in the Leschenault Inlet in the state’s south west.

In Activity 1 of the Marine WATERs Lesson Plan: Life in the Mangroves, students will study what mangroves are. You may wish to use our new Fisheries Fact Sheet: Mangroves, the Poster: The Mysteries of Mangroves and Article: Masters of Adaptation to help facilitate your class discussion.   Then, in Activity 3, students will investigate mangroves as a habitat using a story about a barramundi life cycle. Our Poster: Barramundi Life Cycle will help you to explain the different stages of the life cycle as you work through the story – your students will particularly like the part where the barramundi changes sex from male to female!  In Activity 4, students will use the mangrove ecosystem they created in Activity 3 to develop their knowledge of food webs (for more information on food chains and food webs, check out the Marine WATERs Lesson Plans: SEE Food & Marine Connections).

ACSSU072, ACSSU043, ACSSU112, ACSSU176.

Eggs in the sea…

Posted on: April 4, 2012

Port Jackson shark egg case

It’s Easter time! Whilst you’re consuming all that chocolate, take a moment to stop and think about what the eggs actually mean. We have eggs, chicks and rabbits at Easter to represent new life.

How does new life occur in the ocean though? Many will be familiar with annual coral spawning events that occur around the world. In Western Australia, at Ningaloo, the coral spawning event usually occurs after the full moon in March or April.

Many organisms in the ocean reproduce externally, meaning they release either sperm or eggs (or both in the case of hermaphrodites) into the water. Animals that reproduce in this way release large numbers of eggs and sperm to ensure that some survive.

Other animals, such as some sharks and rays, reproduce via internal fertilization and bear live young. These animals produce fewer offspring, however, have a greater chance of survival.

Use our Seacrets to Sex and Survival poster and Sex and the Sea article to find out more about how a range of marine animals reproduce, including sea stars, sea horses, sea slugs and deep-sea anglerfish! Investigate the methods these animals use to ensure survival of their species, and what challenges do they face? Which animals use external fertilization, and which use the internal method? Do sharks lay eggs, or give birth to live young?  How do you attract a mate if you are a crustacean, dhufish, or cuttlefish? Who gets the job of looking after the baby in the seahorse family?

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