Fish Distribution in Australia and New Guinea

Waters of Australia and New Guinea.

Australia, the smallest part of the world, is a land mostly scorched and inhospitable. The continent includes scattered archipelagos and islands of Oceania, among which the main ones are New Guinea, New Zealand, and Tasmania. Australian nature is unlike that of any other continent. The main watershed of the mainland is the Great Dividing Range, from the slopes of which flow the largest and fullest rivers. These rivers are fed almost exclusively by rain. The western plateau is almost devoid of watercourses, and on the eastern, western, and northern coasts we find only short rivers. Apart from the largest rivers Murray and Darling, only periodic streams carry their waters from the central part of the mainland to endorheic water bodies.

The main river arteries of Australia are the Murray River and its major tributaries the Darling, Murrumbidgee, and Goulburn. The longest river is the Darling River, with a length of 2,800 km. This river never dries up. During the heat period, its bed turns into a chain of bays and small semicircular lakes. Most of Australia’s lakes are waterless basins covered with salt-bearing clays. In those rare cases when they are filled with water, they are muddy, salty, and shallow water bodies. There are many such lakes on the Western Plateau in Western Australia, but the largest of them are located in South Australia: Lake Eyre, Lake Torrens, Lake Gairdner, and Lake Frome. Along the southeastern coast of Australia, numerous lagoons with brackish or salt water have developed, separated from the sea by sandbars and ridges. The largest freshwater lakes are located in Tasmania.

New Guinea is a large island in the Pacific Ocean with an area of 829 thousand sq. km. The island has an equatorial climate; 4/5 of New Guinea’s area is covered with tropical rainforests, with many short but fairly full-flowing rivers. Most of New Guinea is occupied by mountains. The island is divided by a mountain chain practically in half into northern and southern parts: each part is characterized by its own ichthyofauna. The southern part of the island is an extensive lowland plain, undulating in places, crossed by numerous rivers, and heavily swamped in the southwest.

In the Indonesian part of the island of New Guinea, there are over 30 major rivers flowing from the Maoke Mountains north into the Pacific Ocean, such as the Mamberamo River (over 500 km), or south into the Arafura Sea. One of the most significant is the Digul River (400 km), which originates in the Jayawijaya Mountains and flows into the Arafura Sea. New Guinea, as well as the tropical and subtropical parts of the Australian continent, abounds in magnificent water bodies still untouched by civilization and correspondingly clean. Water analysis almost always indicates its softness, and the pH tends towards acidity. Lake Murray in the center of the district is the largest floodplain lake in Papua New Guinea and during the rainy season increases its area fivefold, flooding over 400 sq. km of meadows and valleys. On the plains, average monthly temperatures range from 25 to 28°C.

It is generally accepted that Australia and New Guinea represent those living spaces where rainbowfishes inhabit. Several species of Melanotaeniidae are kept by domestic aquarists. These fish are found in both Australia and New Guinea. They inhabit small rivers and streams, where the water can be either transparent or turbid due to suspended clay particles. In most water bodies where rainbowfishes live, the water is slightly alkaline, with a pH of 7 to 7.8. Hardness varies in a fairly wide range: 4-12°dGH, and the water temperature is 24-28°C. All species from this family have a bifurcated dorsal fin, which is why it was previously believed that they had a marine origin. For their maintenance and breeding, abundant salt supplements and not very soft water were recommended. With a few exceptions, the water in the biotopes is very soft everywhere, and the pH is slightly shifted towards acidity.

Exceptions include those areas whose geological structure is dominated by limestone, and where water areas are under the influence of the sea — such as the area near the town of Katherine with its natural landmark, Katherine Gorge: here the river has carved narrow crevices into the soft rock. An aquarium with fish from the Australian region should have clean, fresh water with a neutral or slightly alkaline reaction (pH 7-7.8); hardness does not play a significant role. The aquarium can be decorated with stones.