Battle of Backbone Mountain

The Australian weasel shark (Hemigaleus australiensis) is an uncommon species of ground shark in the family Hemigaleidae. It inhabits shallow waters off northern Australia to a depth of 170 m (560 ft); smaller sharks frequent sand and seagrass habitat and shift to coral reefs as they grow older. A slim, drab species reaching a length of 1.1 m (3.6 ft), it has sickle-shaped fins with dark tips on the second dorsal fin and caudal fin upper lobe. Its upper teeth are broad with strong serrations only on the trailing edge. The lateral line along each side is prominent and exhibits a downward curve below the second dorsal fin.

Feeding almost exclusively on octopuses and other cephalopods, the Australian weasel shark mostly hunts near the sea floor. It is viviparous, with the developing embryos nourished through a placental connection and born after a six-month gestation period. This species is productive for a shark, with females bearing litters of 1–19 pups usually twice per year. The Australian weasel shark is caught by trawl and to a lesser extent gillnet and longline fisheries, though not in such numbers that its population is threatened. Thus, it has been listed as Least Concern by the International Union for Conservation of Nature (IUCN). (Full article...)

The blacktip reef shark (Carcharhinus melanopterus) is a species of requiem shark, in the family Carcharhinidae, which can be easily identified by the prominent black tips on its fins (especially on the first dorsal fin and its caudal fin). Among the most abundant sharks inhabiting the tropical coral reefs of the Indian and Pacific Oceans, this species prefers shallow, inshore waters. Its exposed first dorsal fin is a common sight in the region. The blacktip reef shark is usually found over reef ledges and sandy flats, though it has also been known to enter brackish and freshwater environments. It typically attains a length of 1.6 m (5.2 ft). Like other sharks, the females are larger than the males.

The blacktip reef shark has extremely small home ranges and exhibits strong site fidelity, remaining within the same local area for up to several years at a time. It is an active predator of small bony fish, cephalopods, and crustaceans, and has also been known to feed on sea snakes and seabirds. Accounts of the blacktip reef shark's life history have been variable and sometimes contradictory, in part reflecting geographical differences within the species. Like other members of its family, this shark is viviparous, with females giving birth to two to five young on a biennial, annual, or possibly biannual cycle. Reports of the gestation period range from 7–9, through 10–11, to possibly 16 months. Mating is preceded by the male following closely behind the female, likely attracted by her chemical signals. Newborn sharks are found further inshore and in shallower water than adults, frequently roaming in large groups over areas flooded by high tide. (Full article...)

In biology, the electric organ is an organ that an electric fish uses to create an electric field. Electric organs are derived from modified muscle or in some cases nerve tissue, called electrocytes, and have evolved at least six times among the elasmobranchs and teleosts. These fish use their electric discharges for navigation, communication, mating, defence, and in strongly electric fish also for the incapacitation of prey.

The electric organs of two strongly electric fish, the torpedo ray and the electric eel were first studied in the 1770s by John Walsh, Hugh Williamson, and John Hunter. Charles Darwin used them as an instance of convergent evolution in his 1859 On the Origin of Species. Modern study began with Hans Lissmann's 1951 study of electroreception and electrogenesis in Gymnarchus niloticus. (Full article...)

Ampullae of Lorenzini (sg.: ampulla) are electroreceptors, sense organs able to detect electric fields. They form a network of mucus-filled pores in the skin of cartilaginous fish (sharks, rays, and chimaeras) and of basal bony fishes such as reedfish, sturgeon, and lungfish. They are associated with and evolved from the mechanosensory lateral line organs of early vertebrates. Most bony fishes and terrestrial vertebrates have lost their ampullae of Lorenzini. (Full article...)

The whale shark (Rhincodon typus) is a slow-moving, filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of 18.8 m (61.7 ft). The whale shark holds many records for size in the animal kingdom, most notably being by far the most massive living non-cetacean animal. It is the sole member of the genus Rhincodon and the only extant member of the family Rhincodontidae, which belongs to the subclass Elasmobranchii in the class Chondrichthyes. Before 1984 it was classified as Rhiniodon into Rhinodontidae.

Whale sharks inhabit the open waters of all tropical oceans. They are rarely found in water below 21 °C (70 °F). Whale sharks' lifespans are estimated to be between 80 and 130 years, based on studies of their vertebral growth bands and the growth rates of free-swimming sharks. Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and small fishes and pose no threat to humans. (Full article...)

The nervous shark (Carcharhinus cautus) is a species of requiem shark, and part of the family Carcharhinidae, so named because of its timid behavior in regard to humans. It is common in shallow, coastal waters off northern Australia, Papua New Guinea, and the Solomon Islands. A small brownish or grayish shark typically measuring 1.0–1.3 m (3.3–4.3 ft) long, this species has a short, blunt snout, oval eyes, and a relatively large second dorsal fin. The leading margins of most fins are finely edged with black, and the lower caudal fin lobe is black-tipped.

Small bony fishes are the main prey of the nervous shark, while crustaceans, molluscs, and snakes may also be eaten. It is viviparous, with the developing embryos nourished through a placental connection. The details of its life history seem to vary depending on latitude—for example, the timing of the breeding season and the length of the gestation period. Females produce litters of one to six young either annually or biennially. The harmless nervous shark is caught incidentally by coastal gillnet fisheries and perhaps also by line and trawl fisheries. The International Union for Conservation of Nature (IUCN) has been listed under Least Concern. (Full article...)

The Izak catshark or simply Izak (Holohalaelurus regani) is a species of catshark, belonging to the family Scyliorhinidae, common off the coasts of South Africa and southern Namibia. It typically inhabits the outer continental shelf at depths of 100–300 m (330–980 ft), with the males found deeper than the females and juveniles. The Izak catshark has a short, wide, flattened head and a robust body tapering to a long, slender tail. It can be identified by its ornate color pattern of dark brown spots (in juveniles) or reticulations and blotches (in adults) on a light yellowish background, as well as by the enlarged dermal denticles over its pectoral fins and along its dorsal midline from the snout to the second dorsal fin. This species reaches 69 cm (27 in) in length, with the males larger than females.

Bottom-dwelling and perhaps relatively active in nature, the Izak catshark feeds mainly on a diverse array of bony fishes, crustaceans, and cephalopods. A significant portion of its diet may be scavenged from offal discarded by fisheries. This species is oviparous, with females producing encapsulated eggs two at a time year-round. The Izak catshark is regularly caught incidentally by a South African bottom trawl commercial fishery, but is discarded rather than utilized. Despite the fishing pressure, its population has been increasing and thus the International Union for Conservation of Nature (IUCN) has assessed it as Least Concern. (Full article...)

The Australian blacktip shark (Carcharhinus tilstoni) is a species of requiem shark, in the family Carcharhinidae, endemic to northern and eastern Australia. Favoring the upper and middle parts of the water column, it can be found from the intertidal zone to a depth of 50 m (160 ft). Appearance-wise this species is virtually identical to the common blacktip shark (C. limbatus), from which it can be reliably distinguished only by its lower vertebra number and by genetic markers. Generally reaching 1.5–1.8 m (4.9–5.9 ft) in length, it is a fairly stout-bodied, bronze-colored shark with a long snout and black-tipped fins.

Primarily piscivorous, the Australian blacktip shark forms large groups of similar size and sex that tend to remain within a local area. It exhibits viviparity, meaning that the unborn young are provisioned through a placental connection. There is a well-defined annual reproductive cycle with mating occurring in February and March. Females bear one to six pups around January of the following year, after a 10-month gestation period. The Australian blacktip shark is among the sharks most commonly caught by northern Australian commercial fisheries. It is mainly valued for its meat, which is sold as "flake". This species was an important catch of a Taiwanese gillnet fishery that operated from 1974 to 1986, and of the Australian Northern Shark Fishery that continues to the present day. As current fishing levels are not thought to threaten this shark's population, the International Union for Conservation of Nature (IUCN) has assessed it as Least Concern. (Full article...)

The porcupine ray (Urogymnus asperrimus) is a rare species of stingray in the family Dasyatidae. This bottom-dweller is found throughout the tropical Indo-Pacific, as well as off West Africa. It favors sand, coral rubble, and seagrass habitats in inshore waters to a depth of 30 m (100 ft). A large and heavy-bodied species reaching 1.2–1.5 m (3.9–4.9 ft) in width, the porcupine ray has a nearly circular, plain-colored pectoral fin disc and a thin tail without any fin folds. Uniquely within its family, it lacks a venomous stinging spine. However, an adult ray can still defend itself ably with the many large, sharp thorns found over its disc and tail.

The diet of the porcupine ray consists mainly of benthic invertebrates and bony fishes, which it digs up from the sea floor. It is aplacental viviparous, in which the developing embryos are nourished by histotroph ("uterine milk") produced by the mother. The porcupine ray has long been valued for its rough and durable skin, which was made into a shagreen leather once used for various utilitarian and ornamental purposes, such as to cover sword hilts and shields. It is caught incidentally by coastal fisheries. Because it must be handled carefully due to its thorns, its commercial significance is limited. Unregulated fishing has led to this species declining in many parts of its range, thus it has been listed as Vulnerable by the International Union for Conservation of Nature. (Full article...)

Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their elongated rostra, which are thought to enhance electroreception to detect prey. Paddlefish have been referred to as "primitive fish" because the Acipenseriformes are among the earliest diverging lineages of ray-finned fish, having diverged from all other living groups over 300 million years ago. Paddlefish are almost exclusively North American and Chinese, both extant and in the fossil record.

Eight species are known - six extinct species known only from fossil remains (five from North America, one from China), one extant species, the American paddlefish (Polyodon spathula), which is native to the Mississippi River basin in the U.S., and the Chinese paddlefish (Psephurus gladius), declared extinct in 2022 following a 2019 recommendation that it be declared extinct. The species was last sighted in 2003 in the Yangtze River Basin in China. Chinese paddlefish are also commonly referred to as "Chinese swordfish", or "elephant fish". The earliest known species is Protopsephurus from the Early Cretaceous (Aptian) of China, dating to around 120 million years ago. (Full article...)

The jamming avoidance response is a behavior of some species of weakly electric fish. It occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish shifts its discharge frequency to increase the difference between the two. By doing this, both fish prevent jamming of their sense of electroreception.

The behavior has been most intensively studied in the South American species Eigenmannia virescens. It is also present in other Gymnotiformes such as Apteronotus, as well as in the African species Gymnarchus niloticus. The jamming avoidance response was one of the first complex behavioral responses in a vertebrate to have its neural circuitry completely specified. As such, it holds special significance in the field of neuroethology. (Full article...)

The peppered maskray (Neotrygon picta) or speckled maskray, is a species of stingray in the family Dasyatidae, found in shallow waters off northeastern Australia. This small, thin-bodied ray attains a maximum width of 32 cm (13 in). It has a diamond-shaped pectoral fin disc with a row of tiny thorns along the midline, and a relatively short, whip-like tail with both upper and lower fin folds. Its upper surface has a speckled color pattern consisting of black spots and brownish reticulations on a light yellow to brown background.

Favoring soft-bottomed habitats, the peppered maskray is a bottom-dwelling predator consuming mainly crustaceans (particularly caridean shrimp) and polychaete worms. It is viviparous, with litter sizes of one to three. The females supply their developing young with histotroph ("uterine milk") during gestation. Although the peppered maskray is a frequent bycatch of bottom trawl fisheries, it is still common and significant portions of its population appear to lie within unfished waters. As a result, the International Union for Conservation of Nature (IUCN) has assessed it as Least Concern. (Full article...)

The Devils Hole pupfish (Cyprinodon diabolis) is a critically endangered species of the family Cyprinodontidae (pupfishes) found only in Devils Hole, a water-filled cavern in the US state of Nevada. It was first described as a species in 1930 and is most closely related to C. nevadensis and the Death Valley pupfish (C. salinus). The age of the species is unknown, with differing analyses offering ranges between one thousand and sixty thousand years. It is a small fish, with maximum lengths of up to 30 mm (1.2 in). Individuals vary in coloration based on age and sex: males are bright metallic blue while females and juveniles are more yellow. A defining trait of this species is its lack of pelvic fins. The pupfish consumes nearly every available food resource at Devils Hole, including beetles, snails, algae, and freshwater crustaceans, with diet varying throughout the year. It is preyed on by the predaceous diving beetle species Neoclypeodytes cinctellus, which was first observed in Devils Hole in 1999 or 2000. Reproduction occurs year-round, with spikes in the spring and fall. Females produce few eggs and the survivorship from egg to adult is low. Individuals live 10–14 months.

Devils Hole is more than 130 m (430 ft) deep, though pupfish are only found in the upper 24 m (80 ft). The water is a constant temperature of 33 °C (91 °F) and dissolved oxygen levels are low. A small, shallowly submerged rock shelf provides critical feeding and spawning habitat for the pupfish. Nearby agricultural irrigation in the 1960s and 1970s caused the water to drop in Devils Hole, resulting in less and less of the shelf remaining submerged. Several court cases ensued, resulting in the Supreme Court case Cappaert v. United States, which determined that the preservation of Devils Hole as a National Monument in 1952 implicitly included preservation of adequate groundwater to maintain the scientific value of the pool and its fauna. Other threats faced by the species include flash floods, earthquakes, and vandalism. (Full article...)

The convict cichlid (Amatitlania nigrofasciata) is a fish species from the family Cichlidae, native to Central America, also known as the zebra cichlid. Convict cichlids are popular aquarium fish and have also been the subject of numerous studies on fish behaviour. (Full article...)

The zebra shark (Stegostoma tigrinum) is a species of carpet shark and the sole member of the family Stegostomatidae. It is found throughout the tropical Indo-Pacific, frequenting coral reefs and sandy flats to a depth of 62 m (203 ft). Adult zebra sharks are distinctive in appearance, with five longitudinal ridges on a cylindrical body, a low caudal fin comprising nearly half the total length, and usually a pattern of dark spots on a pale background. Young zebra sharks under 50–90 cm (20–35 in) long have a completely different pattern, consisting of light vertical stripes on a brown background, and lack the ridges. This species attains a length of 2.5 m (8.2 ft).

Zebra sharks are nocturnal and spend most of the day resting motionless on the sea floor. At night, they actively hunt for molluscs, crustaceans, small bony fishes, and possibly sea snakes inside holes and crevices in the reef. Though solitary for most of the year, they form large seasonal aggregations. The zebra shark is oviparous: females produce several dozen large egg capsules, which they anchor to underwater structures via adhesive tendrils. Innocuous to humans and hardy in captivity, zebra sharks are popular subjects of ecotourism dives and public aquaria. The World Conservation Union has assessed this species as Endangered worldwide, as it is taken by commercial fisheries across most of its range (except off Australia) for meat, fins, and liver oil. There is evidence that its numbers are dwindling. (Full article...)