Trout cod facts for kids
Quick facts for kids Trout cod |
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The trout cod (Maccullochella macquariensis), also called the bluenose cod, is a large freshwater fish found in Australia. It belongs to the same family as the Murray cod. This fish used to live all over the south-east part of the Murray-Darling River system. Sadly, it is now an endangered species.
In the past, especially in the 1800s and early 1900s, people knew this fish as the bluenose cod. This was especially true in Victoria. In some parts of New South Wales, it was called the trout cod. When scientists confirmed it was a unique species in the 1970s, they chose the name trout cod. This name can be a bit confusing. Trout cod are native Australian fish. They are not a mix of Murray cod and introduced trout.
The trout cod is listed as an endangered species by many groups. This includes the New South Wales Fisheries Management Act 1994 and the Australian Commonwealth's Environment Protection and Biodiversity Conservation Act 1999. It is also listed by the World Conservation Union (IUCN).
Scientists have found fossils of fish from the Maccullochella group that are millions of years old. The trout cod species itself has been around for at least 3.6 to 5.3 million years.
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About the Trout Cod
Trout cod can grow quite large. They have been reliably measured up to 80 centimeters (about 31 inches) long and can weigh 16 kilograms (about 35 pounds). Some people even say they have seen bigger ones!
Trout cod look a lot like Murray cod, but there are some clear differences.
What Does a Trout Cod Look Like?
Trout cod are medium-sized fish with a deep, long body. It is round if you look at it from the front. Unlike Murray cod, trout cod have a pointed head. Their top jaw sticks out over the bottom jaw. The top of their head is straight. Their eyes are a bit bigger than a Murray cod's. You can often see a dark stripe through their eye.
The belly of a trout cod is usually cream or light grey. Their back and sides are often bluish-grey. They have irregular black spots all over their back and sides. The color can change depending on where they live. It can range from almost white to light grey-green, light brown, or even almost black. The black spots on their back and sides are always there.
The fins of a trout cod are also unique. The spiny fin on its back is medium height. It is partly separated from the soft, rounded fin behind it. The soft back fin, the fin on its belly (anal fin), and the tail fin are all large and rounded. They are light to dark grey or black with clear white edges. The large, rounded fins on their sides (pectoral fins) are usually the same color as their body. The fins on their underside (pelvic fins) are large and angled. They are set forward of the pectoral fins. The white front rays on the pelvic fins split into two white threads. The pelvic fins themselves are usually a see-through cream or light grey.
Smaller trout cod are thinner than Murray cod of the same size. Interestingly, very large trout cod seem to have deeper shoulders than large Murray cod.
Even though trout cod were only officially named a separate species in 1972, fishermen and early scientists knew they were different. They noticed the trout cod's different look. They also saw that trout cod preferred cooler, faster-flowing water in upland areas.
Where Trout Cod Live
Trout cod are a special type of fish that prefer upland rivers and creeks. They often share these homes with Macquarie perch and blackfish. Historical records show that trout cod mainly lived in these higher-altitude areas.
It's common for native fish in the Murray-Darling system to have both upland and lowland species. Here are some examples:
| Upland Fish | Lowland Fish |
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| Macquarie perch, Macquaria australasica | Golden perch, Macquaria ambigua |
| Australian bass, Macquaria novemaculeata | Estuary perch, Macquaria colonorum |
| Two-spined blackfish, Gadopsis bispinosis | River blackfish, Gadopsis marmoratus |
| Mountain galaxias species, Galaxias spp. | Flathead galaxias, Galaxias rostratus |
Trout cod often stay near cover, like logs or rocks. They prefer faster currents and cooler water than Murray cod. Their diet is similar to Murray cod, but adjusted for their size. They eat other fish, freshwater mussels, crustaceans, and aquatic insects. They also eat small mammals and water birds. Recent observations suggest that land insects are a big part of their diet in upland rivers.
In the wild Murray River population, trout cod tend to stay in deep water near banks. They like areas with snags, rocks, or other large structures. However, old stories say that trout cod in upland rivers were often found in shallow, fast-flowing areas. Trout cod usually have small home ranges. They might not move far from their home, except during breeding season. During breeding, they swim upstream, like many other Murray-Darling fish. It is thought that they return to their original spot after breeding.
What Trout Cod Eat
Trout cod are carnivores, meaning they eat other animals. They feed on other fish and crustaceans. This includes crayfish, yabbies, and freshwater shrimp. They also eat insects that live in water and on land. Young trout cod, called larvae, float in the water and eat tiny water creatures called zooplankton.
Trout Cod Life Cycle
Trout cod become ready to have babies when they are 3 to 5 years old. This is when males are about 35 centimeters (14 inches) long and females are about 43 centimeters (17 inches) long. Trout cod become mature at a smaller size than Murray cod. This helps them survive in the rocky, less nutrient-rich upland habitats where they live.
No one has ever seen trout cod spawn in the wild, so we don't know much about it. It is thought to be similar to Murray cod spawning. However, it happens about three weeks earlier and in much colder water. Trout cod are believed to spawn in water as cold as 15 degrees Celsius (59 degrees Fahrenheit) in upland rivers. They use rocks to lay their eggs. This is another way they are adapted to cool, rocky rivers.
Unlike Murray cod, trout cod will not breed in man-made dirt ponds. This shows they are more specialized for upland areas. For conservation efforts, scientists use hormone injections to help them breed. Trout cod can breed with Murray cod. So, it's important not to put Murray cod in places where trout cod already live, unless they are already living together naturally.
Saving the Trout Cod
Trout cod used to be very common in the Murray-Darling Basin. But now, they are listed as endangered by the IUCN. This is because of too much fishing, damage to their homes, and the introduction of invasive trout species. The trout cod is now fully protected. Only one wild population of trout cod is left in the Murray River. This area is a mix of upland and lowland river habitat.
In lowland rivers, things like dams, removing logs from rivers, and too much fishing have caused their numbers to drop. Many introduced redfin perch also ate a lot of native fish, including trout cod. It's possible that trout cod populations in lowland areas came from upland populations over time. However, old records suggest that lowland trout cod were not as common as other native fish like Murray cod and golden perch. So, it might be hard to create strong trout cod populations in lowland areas. We need to focus on protecting and restoring their upland homes, especially making some areas free of introduced trout.
Historical information shows that trout cod were common in most of the larger upland rivers and streams in the south-east Murray-Darling system. These upland rivers were their main homes. It's a big problem that trout cod have disappeared from all their upland river homes. Many of these upland rivers still have good quality habitat that hasn't been badly damaged. While dams and pollution have hurt trout cod in some places, it's almost certain that the main reason they disappeared from good quality upland rivers is the presence of introduced trout species. These trout are aggressive and eat young trout cod.
Every large upland river and stream in south-eastern Australia is now full of introduced trout (rainbow trout and brown trout). Many have been stocked with these trout for over a hundred years. Not a single large upland river has been kept free of trout for native fish. This has had a terrible effect. Events like droughts or bushfires have made it worse. After these events, introduced trout were put back, but native fish were not. This means that many upland native fish, like trout cod, have almost completely disappeared from their homes. They can't cope with the huge number of introduced trout eating their young and competing for food and space.
Here is a story from an old fisherman:
I met a man who worked at Tom Groggin Station before World War I. He told me he used to fish in the Indi River. It had many blue nose [trout cod], white eye [Macquarie perch], and greasies [blackfish]. He even dreamed of fishing there while he was at war. When he came home, he went fishing right away. He quickly caught a fish he had never seen before, about 30cm long. It was spotted and nicely shaped. He took it home, thinking it was unique. They told him it was a brown trout. From that time, the numbers of white eye and blue nose went down, while brown and rainbow trout increased. This man saw a clear change in the fish in the Indi River.
Heads and Tales: Recollections of a Fisheries and Wildlife Officer.
We really need scientific studies to understand how introduced trout affect trout cod in upland rivers. This would help us find better ways to save trout cod. However, many people and fishing groups prefer introduced trout, so these studies might take a while.
Two small groups of trout cod have been created by hatcheries in the Murrumbidgee River at Gundagai and Narranderra. These groups seem to be breeding. However, it's not clear if they will survive on their own in the long term. Many other attempts to stock trout cod have failed. This is often because too few young trout cod were released. Also, they were often put into rivers where introduced trout were already strong. In one case, many more introduced trout were released at the same time.
A semi-natural group of trout cod lives in a small upland stream called Seven Creeks. This group was started in the 1920s by moving trout cod (and Macquarie perch) above some waterfalls. This population is not completely artificial. Some of the trout cod moved there came from below the falls.
- Froese, Rainer and Pauly, Daniel, eds. (2005). "Maccullochella macquariensis" in FishBase. 10 2005 version.
- Native Fish Australia Trout cod page
- Australian Government Department of the Environment and Heritage - Recovery Plan for the Trout Cod Maccullochella Macquariensis 1998 - 2005
- Australian Museum - Australian Museum Fish Site
- New South Wales Department of Primary Industries - cod recovery plan
- New South Wales Department of Primary Industries - cod fishnote
- Sepkoski, Jack Sepkoski's Online Genus Database
- Description (in French) Grystes Macquariensis, "le growler de la rivière Macquarie", p. 58 in Cuvier and Valenciennes Histoire naturelle des poissons, tome 3.
- Illustrations: figure 2 of plate 12 in Griffith & Smith 1834.
