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BULLROUT – Notesthes robusta
Rob McCormack
Bullrouts are a member of the Scorpion Fish Family (Scorpaenidae) and are feared by most people due to their venomous spines. A native of Eastern flowing steams of NSW and Queensland in Australia they inhabit both fresh and salt water. Luckily to date I have not been spiked by them as even though we handle them every week I take extreme care as the horror stories that customers tell us of their experiences, the pain and swelling are frightful.
I grow bullrouts for the aquarium trade for those enthusiasts who want something different in their tanks. They are a very tough hardy species which are perfect for tanks with other aggressive territorial species such as Barras, Cod, and Oscars etc. They are basically a nocturnal species which become quite active in the tank at night, but during the day just basically pretend to be a rock hardly moving except if food comes its way then it will inhale it and back to motionlessness.
Bullrouts grow large to over 600grams but generally the ones we sell are in the 100 to 250 gram range. They can live happily in both marine and freshwater and anything in-between. They live on a diet of shrimp, fish, worms and yabbies. Also some indications they eat weed as they do regurgitate weed into our tanks after capture from the ponds but it is not clear wether they have specifically eaten the aquatic weed or if this has just been consumed as an added extra when eating the shrimp living in the weed beds. In our tanks we feed them gambusia, shrimp and yabbies which we have plenty of.
Not a lot known in the literature available on breeding bullrouts. We capture rowed up females and running males in April (autumn) and they do seem to school up after heavy rain at that time in this region. Males always seem to be smaller than females from our experience. For example we captured some breeding stock to do some artificial breeding experiments in our hatchery this year. We finish breeding Silver and Golden Perch in March and do not start breeding Bass, Mullet and Bream till May so decided to do some Bullrouts for fun/terror in April.
We went down to the local hardware and purchased a set of leather riggers gloves and a set of PVC heavy duty gauntlets and but on both pairs before handling them and it worked A OK. We captured a total of 38 Bullrouts ready to breed on the 7th and 8th April 2003. Of those 38 fish only 7 were males and weighed in from 95 to 175 grams. The balance were all females from 210 gram to 550 gram. All were gravid with an extremely swollen abdomen.
Knowing nothing about the breeding of Bullrouts we just decided to give it a go and see what happens. We have heard reports that small bullrouts are seen in freshwater impoundments where access to salt water is prohibited so we decided to breed them in fresh and see what happened. We tried injecting them with HCG a human gonadotrophin at the same rates we would try with Australian Bass. We did this as a starting point as we regularly catch them in the wild in our bass nets. Females we injected at a rate of 1000i.u./kg and males at 250i.u./kg. The freshwater was kept at 18 deg C as this is the temperature we do the bass at and equivalent to river temperatures in the region at this time of the year. Results of this were basically the males were fine but the females died in the tanks. We did get some eggs in the tanks before they died but none were fertile and they did not hatch.
Results from our first freshwater attempt were not clear as we did not know if they bred as individual pairs or as a school type fish. In the fresh water we tried one tank with a single pair. Another tank with 2 pairs and the third tank with 4 pairs. The first tank with the single pair had no eggs. The other 2 tanks with multiple pairs both had some eggs. That effort was a waste but we learnt a bit and then we tried it in salt water at a salinity of 24 – 28 ppm salt.
For our salt water test we decided to repeat the experiment but with a 250i.u. dosage rate across the board as obviously the first test rates were too high resulting in death not breeding.
We repeated the test in salt water in 3 different tanks with one pair, two pairs and three pairs. At a 250 i.u. dose rate all tanks and all females spawned 80 – 100% with zero mortality.
We will repeat the experiments in the future with lower dosage rates and lower salinity levels and eventually over time we will work out the best combination for perfect results.
MOSQUITO FISH/MINNOWS Gambusia holbrooki
Rob McCormack
Mosquito Fish are extremely common and inhabit both fresh and salt water in NSW. Frankly there is not much of NSW that you will not find the hated Mosquito fish. They do prefer warm water so as you go higher up the river catchments they do become less common. On the lower flats and plains they are a major problem....................................
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MURRAY COD – Maccullochella peelii peelii
Murray Cod are natives of the Murray Darling drainage basin of Australia. They are a predatory fish with excellent eating qualities. They can be captured on baits and lures but are not very common or easy to capture. They grow to over 100kgs in size and are the top of the food chain in our rivers. Due to their rarity, difficulty to capture, large size and great taste these are the ultimate challenge for most freshwater anglers in the Southern States of Australia.
Murray Cod are listed as a vulnerable species and State Government and private fish hatcheries produce millions of fingerlings each year for stocking in the wild and for aquaculture. All cod hatcheries in NSW are located west of the Great Divide as per NSW Fisheries regulations it is illegal to hatch cod on the eastern drainage. It is also illegal to stock ponds or dams on the Eastern Drainage with Cod; however, you can culture them in tanks.
Cod are an excellent species for aquaculture. They are quite easily weaned onto pellets and grow well on pellet diets. Cod fingerlings grown in tanks within a recirculation system will usually attain a size of 500gram in 12 months (everything at optimum). Cod are prized for both their colour and eating qualities so attract a good price at the markets. Demand for cod fingerlings is high within the aquaculture industry and there does always seem to be a shortage of fingerlings available. Cod are generally bred naturally in a farm dam type situation. Artificial breeding structures are usually placed into the dam for cod to use. Hollow logs and 44gallon drums are usually used with a liner attached to the inside of the hollow container. Cod breed inside the structure and their eggs become attached to the liner which is removed to hatchery tanks for the incubation and hatching of the juvenile codlings.