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Fishy facts

The nuisance of the ocean

Posted on: November 27, 2012

Common blowfish

The common blowfish is often regarded as a nuisance to fishers, gobbling bait before any other species can get near it.  However, these fish are native to Western Australia (and therefore are not pests) and play an important role in keeping our marine ecosystems clean by eating waste bait and berley.

Common blowfish are found along the lower west coast of WA but also have a northern relative.  The northwest blowfish inhabits northern Australian waters but is also occasionally seen off the lower west coast as far south as Cape Naturaliste. Northwest blowfish are significantly larger than the common blowfish, reaching a maximum of 88 cm in length, compared to the common blowfish at 22 cm.

Both species of blowfish contain a highly lethal toxin so they are not generally targeted by fishers– however they still have a bag limit. Visit the Department of Fisheries website to find out more about bag and size limits in your area. To learn more about other ways we manage recreational fisheries in Western Australia, see the Marine WATERs lesson plan: Fishing for the Future.  

Fishers are reminded not to leave blowfish to die on beaches and jetties as pets have died from eating them.

Want to know more about this species or of the many other species found in Western Australia? See our extensive range of fact sheets.

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’.

Feeling peckish?

Posted on: April 23, 2012

Imagine your life if you were a fish – your main concerns on a daily basis would be finding food, not becoming food yourself, rest, finding food, not becoming food, find a mate, rest, finding food …

Luckily for us, finding food usually extends as far as visiting the supermarket and ‘catching’ our dinner into a shopping basket.  Our next challenge is then cooking, but at least we don’t have to concern ourselves with being eaten by someone else!

Use the SEE Food Lesson Plan to investigate who eats what in the marine environment.  It begins with plankton, the microscopic plants and animals that form the basis of the food chain (see The Plankton Challenge) and ends with a top level predator – us!  This lesson plan is based on the fantastic book See Food (Windy Hollow books), written by Guundie Kuchling who lives here in Western Australia! 

In Activity 3, students build a food pyramid using organisms from the story and investigate what happens when parts of the pyramid are removed.  Another way to conduct this activity is to write each of the organisms in the food pyramid on cards (in the same ratios as they are in Activity 3).  Give each student a labeled card and a piece of string.  Ask students to hold opposite end of the string with those that they either consume, or are consumed by.  One by one, remove organisms from the group (ask them to let go of the string, and sit down).  As each organism is removed, there will be a domino effect of others who no longer have a food source.  This is a really simple but very visual way of explaining food webs to students.  As an extension on this, try the Tied up in a Marine Food Web activity in the Marine Connections lesson plan.     

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