Dwarfing in bony fish
The dwarfing in bony fish is an evolutionary phenomenon of adaptation of species to specific environmental conditions . As can be observed in other vertebrate groups , this dwarfing leads to a miniaturization of the bone structure and the organs and thus the body size.
Verzwergte fish (English miniature fishes ) are having a group of fish species, the common due to their size characteristics. A species is assigned to this group independently of a phylogenetic system . Weitzman & Vari (1988) investigated the phenomenon of high similarities in small fish. All sexually mature fish with a body length of less than 20 millimeters belong to this morphological group.
The assessment of the body length is difficult in many cases, since male and female fish mostly differ in this characteristic. There is also the extreme case of dwarf males , such as the deep-sea anglerfish Photocorynus spiniceps , in which the males reach a length of only 6.2 millimeters and finally parasitize on the females up to 6 centimeters long. However, this is a special form of sexual dimorphism . As carriers of ovaries and eggs, female fish are often larger than males. In addition, sexual maturity can be recognized comparatively easily in the presence of mature eggs without a complex histological examination. A size comparison of different species and the assignment to the group of small fish is therefore mainly based on the body length of the females, provided they carry mature eggs.
features
The miniaturization of fish goes hand in hand with the reduction of various organs. The tendency to reduce certain structural features, particularly the skeleton, is typical . This is usually not very ossified, rather cartilaginous or completely boneless. Fin rays , scales and the lateral line organ are usually also reduced .
Few eggs are produced, and eggs are large compared to the size of the fish. The animals are pedomorphic . This means that despite sexual maturity they show many characteristics of a larval stage . With a shortened development period and accelerated maturation, the adult animal shows characteristics that otherwise only appear in the larval stage. In contrast, sexual characteristics and organs used for reproduction are developed and clearly expressed.
Small fish have a tendency to be in stagnant or slow-flowing waters, often in nutrient-poor habitats .
Occurrence
The discovery and occurrence of dwarf fish relates to the rare, black-water peat bog forests of Malaysia . Typical for these forests are meter-thick, soft peat layers on which strongly acidic water forms and in which the trees take root.
For a long time these forests were thought to be poor in species. In the last 20 years, however, a larger number of fish have been discovered here, which show the characteristics typical of the group of dwarfed fish in varying degrees. Paedocypris progenetica , the smallest fish and at the same time the second smallest vertebrate (after Paedophryne amauensis ) known so far , also lives there .
The peat bog forests offer a habitat to which the small fish are optimally adapted. They can survive dry spells in small, shallow pools, ditches, or the damp earth, with their small size being a significant advantage. Even in very dry periods, the sponge-like peat provides a buffer with sufficient fresh water.
threat
The complex ecosystems of the peat bog forests in Southeast Asia are severely threatened and rapidly declining. The reasons for this are the deforestation and drainage for wood and land reclamation and palm plantations and crab farming . These forests suffered severe damage from massive fires in 1997 that lasted for months. It can be assumed that many of the highly specialized fish will be extinct before they are scientifically discovered and explored.
See also
Individual evidence
- ^ SH Weitzman & RP Vari: Miniaturization in South American freshwater fishes; an overview and discussion. Proceedings of the Biological Society of Washington, 101, pp. 444-465, 1988
- ↑ Masaki Miya, Theodore W. Pietsch, James W. Orr, Rachel J. Arnold, Takashi P. Satoh, Andrew M. Shedlock, Hsuan-Ching Ho, Mitsuomi Shimazaki, Mamoru Yabe & Mutsumi Nishida: Evolutionary history of anglerfishes (Teleostei: Lophiiformes): a mitogenomic perspective. BMC Evolutionary Biology, 10, 1, 58, February 2010, Fig. 3 F doi : 10.1186 / 1471-2148-10-58
literature
- M. Kottelat, R. Britz, HH Tan & K.-E. Witte. 2005: " Paedocypris , a new genus of Southeast Asian cyprinid fish with a remarkable sexual dimorphism, comprises the world's smallest vertebrate." Proceedings of the Royal Society B 10.1098 / rspb.2005.3419. Abstract Detailed scientific research report by the Royal Society