New Zealand sand flounder facts for kids
Quick facts for kids New Zealand sand flounder |
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The New Zealand sand flounder (Rhombosolea plebeia) is a type of flatfish found in the waters around New Zealand. It lives in shallow areas, sometimes as deep as 100 meters. People also call it the New Zealand dab, pātiki, diamond, tinplate, or square flounder.
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What Does a Sand Flounder Look Like?
Like other flatfish, sand flounders start their lives looking very different. When they are tiny larvae, they have an eye on each side of their head. They are round and swim upright in the water, just like most fish.
As they grow, something amazing happens. One eye slowly moves to the right side of their head. The other eye stays put. This means one side of their body becomes blind. Their body also flattens out into a diamond shape. Now, they swim flat, parallel to the seabed.
The side of the fish with its eyes is usually a greenish-brown or grey. It might have faint patterns. The other side, which lies on the seabed, is white. Adult sand flounders are usually 25–35 cm long. The biggest ones can reach 45 cm.
During the day, these fish lie on the seabed. They are masters of disguise! They have special cells in their skin. These cells let them change color to match the sand or mud. This makes them almost invisible. Only their bright blue-green eyes might give them away.
When they swim, they move their side fins in a wavy motion. If a predator threatens them, they use their tail to quickly push themselves away. An adult sand flounder technically swims on its side. Its long dorsal fin runs along one edge of its body. Its anal fin runs along the other. These fish do not have a swim bladder. This means they usually stay on the seabed. They only leave it for mating and laying eggs.
Where Do Sand Flounders Live?
Global Home
New Zealand sand flounders are native to New Zealand. This means they are only found there. You won't find them living naturally anywhere else in the world.
New Zealand Locations
These flounders live in most coastal waters around New Zealand. The largest groups are found in Tasman Bay. They are also common along the East Coast of the South Island. You can find them in harbors, inlets, bays, and open ocean waters.
Favorite Places to Live
Sand flounders prefer coastal areas. They are usually found in waters up to 50 meters deep. It is rare to find them deeper than that. They are common on mudflats. However, they can live on many different types of seabeds. This includes sand, clay, pebbles, and gravel. They also live in estuaries, which are where rivers meet the sea.
Young sand flounders, called juveniles, stay in sheltered areas. These include estuaries, mudflats, and sand flats. They usually live there for about two years. They also prefer a mild, temperate climate.
Life Cycle of the Sand Flounder
The time when New Zealand sand flounders lay their eggs depends on where they live. In the northern parts of New Zealand, they lay eggs for a long time. This happens from March to December. In the south, most egg-laying occurs in the spring.
One study in the Hauraki Gulf found something interesting. Female sand flounders can lay a lot of eggs. They lay between 100,000 and 500,000 eggs at one time. The number of eggs depends on the size of the female fish. Bigger females lay more eggs.
After about a week, tiny sand flounder larvae hatch. The exact time depends on the water temperature. These larvae have a large yolk sac under their bodies. This sac gives them food until they can find their own. At this stage, they are less than half a centimeter long. They have an eye on each side of their head. They swim upright, just like most fish.
As they grow, they start eating outside food. They eat tiny seaweed spores and algae. As they get bigger, they eat small shrimp and plankton. This extra food helps them grow quickly. By three weeks old, they are about one and a half centimeters long.
Now, the amazing change begins. Above each eye of the sand flounder, there is a bar of cartilage. The cartilage above the left eye disappears. Then, the left eye starts to move. It slowly travels across the top of the head. It stops right next to the right eye. The sand flounder's mouth also twists into an unusual shape. This happens because its skull and bones move during this change.
While the eye is moving, the sand flounder's body flattens out. It loses its round shape. This big change, called metamorphism, makes swimming upright very hard. The young sand flounders then sink to the bottom. They start swimming like adult flatfish. They wave their side fins. For fast movement, they use their tail.
Young sand flounders move to shallow estuaries and mudflats. They stay there until they are about two years old. This is when they become mature. Once they are grown up, they move to deeper waters. They go to depths of 30 to 50 meters to lay eggs. After this first move, they keep migrating. They go to shallow waters (0-50m) in spring and summer. Then they move to deeper waters (50-100m) in autumn and winter.
Male sand flounders are smaller than females. Males become mature when they are about 10 cm long. They can grow to 15–17 cm. Females grow faster. They are mature at 16–20 cm long. By age two, they can be 23–24 cm. By age three, female sand flounders average 30 cm long. Sand flounders usually live for three to four years. This means they can lay eggs for about two years.
What Do Sand Flounders Eat?
When sand flounders are very young, they get food from a yolk-sac. Once they are big enough, they find their own food. Adult sand flounders are best at finding food at night. They are ambush predators. This means they hide perfectly using their camouflage. Then, they quickly attack prey that comes close.
They eat many different creatures that live on the seabed. These include crabs, brittlestars, shrimps, worms, whitebait, shellfish, and tiny fish. They find their food by touch and sight. They also eat mud and bits of seaweed while they are feeding.
Who Hunts the Sand Flounder?
Humans are a major predator of the New Zealand sand flounder. This fish is very important for commercial fishing in New Zealand.
Flatfish like the sand flounder are excellent at hiding. When they settle on the seabed, they wiggle their fins. This throws up sand or mud onto their bodies. This makes them almost impossible to see. Even with this great camouflage, they still have predators. Some of these include tope sharks, spined dogfish, Maori chief fish, ling, and toadfish.
Sand Flounders and People
The New Zealand sand flounder is a popular fish to catch and eat. People who fish for fun often catch them. They use beach seines, setnets, or spears. The Māori people used to call them ‘Patiki’. They would catch them at night on mud flats. They used torches made of pine to attract the fish. Then, they would easily spear them.
For commercial fishing, sand flounders are caught using trawls and setnets. Sand flounder is very easy to cook. There are many ways to prepare and serve it. A simple way is to wash it, coat it in flour, and fry it. Cook each side in a medium-hot pan with oil or butter until the skin is crispy.
Currently, the number of sand flounders is going down. However, this decline is not happening very fast. They are still common in many areas. Because of this, they are listed as "Least Concern" on the Red List. This means they are not in immediate danger. So, there are no special conservation efforts right now. But, since they are an important commercial fish, scientists need to keep studying them. They need to watch how many are caught and how many fish are in the population. This will help make sure they stay in the "Least Concern" category. It will also help if conservation efforts are ever needed in the future.
