A study of coeval sibling cannibalism in larval and juvenile fishes and its control under culture conditions
- Authors: Pienaar, Anthony Graham
- Date: 1990
- Subjects: Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5781 , http://hdl.handle.net/10962/d1005469 , Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Description: The primary objective of this study was to examine environmental parameters thought to affect cannibalism in certain fish species. It was found that environmental, behavioural, genetic and physiological factors all affect cannibalism in the species exhibiting the phenomenon. The diversity of factors nfluencing cannibalism served to illustrate the complexity of this behaviour pattern. Feeding to satiation was found to suppress cannibalism in catfish, trout and koi carp. High population densities were found to increase the rate of cannibalism, thereby acting as a population regulation mechanism for catfish, trout and the common and koi carps. Live food, as compared with dry pelletized feed was found to significantly suppress cannibalistic aggression. Catfish grown in total darkness, provided with refuges and living in turbid conditions were found to exhibit lowered cannibalistic and territorial aggression. Various lines of evidence suggested that cannibalism has a genetic basis, as was shown by the differences in cannibalistic behaviour of the two strains of Cyprinus carpio, viz. common and koi carp, with cannibalism being higher in the latter. This finding substantiates the hypothesis that cannibalism is genetically controlled and therefore open to evolutionary change. It is concluded that cannibalism is adaptive in times of food limitation, but that it is merely a by-product of normal feeding behaviour when food is abundant. Since cannibalism is advantageous and thus adaptive, the question arises ai to whether selection is occurring at the individual or the population level (or both). It was concluded that it is acting at the individual level, and that any benefits accruing at the population level iv were simply the effect of the initial cause, viz. individual selection. One of the aims of this study was to determine whether cannibalistic tendencies in fish are influenced by differing life history style trajectories. Based on the results of this study it is hypothesized that cannibalism is an r-selected trait. wi th the understanding gained from the knowl edge of the fundamental principles governing cannibalism, certain recommendations for its control in fish culture could be made. It is, however, imperative that further intensive studies be carried out to understand more fully this complex subject. General "rules" for regulating cannibalism could be helpful for any given cannibalistic species. However, in considering the differing life-history styles of each species, it becomes evident that species-specific guidelines need to be worked out. Until then, any suggestions for cannibalistic control offered to the aquaculturist can only serve as unrefined tools.
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- Date Issued: 1990
An index and bibliography of eel larvae
- Authors: Castle, P H J (Peter Henry John) , Rhodes University. J.L.B. Smith Institute of Ichthyology
- Date: 1969-12
- Subjects: Eels , Fishes -- Larvae , Fishes -- Bibliography , Leptocephalous larvae
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/69608 , vital:29558 , Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB)) Periodicals Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB))
- Description: Online version of original print edition of the Special Publication of the J.L.B. Smith Institute of Ichthyology; No. 7 , A survey of ichthyological literature from 1758 until the end of 1968 reveals that information on eel larvae (leptocephali) is widely scattered and contained in at least 600 different papers. A synthesis of tlris information, essential for the correlation of larval eels with their adult species, is attempted here as a necessary adjunct to the further development of systematic studies on adults. About 450 forms of eel larvae have been described, of which nearly 100 have been at least tentatively identified; some 200 have been named as species of die genus Leptocephahis Grono- vius, 1763 (now a rejected name in Zoology), or of other larval genera; the remainder have not been named. Systematic and bibliographic information on these cel larvae is presented together with a geographic checklist and a list of myomere numbers in leptocephali. Reports of eel eggs and prelarvae are not included but these may be found in some of the papers listed. The leptocephalous larvae of other groups of fishes are excluded from this index, although references are made to relevant sources of information.
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- Date Issued: 1969-12
Eggs and early larvae of the congrid eel Gnathophis capensis off Southern Africa
- Authors: Castle, P H J (Peter Henry John) , Rhodes University. J.L.B. Smith Institute of Ichthyology
- Date: 1969-03
- Subjects: Eels , Fishes -- Larvae , Gnathophis capensis
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/69563 , vital:29549 , Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB)) Periodicals Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB))
- Description: Online version of original print edition of the Special Publication of the J.L.B. Smith Institute of Ichthyology; No. 5 , Two hauls made in late January, 1930 off southern Africa by the Danish Dana Expedition contained developing eggs and very young larvae of the congrid eel Gnathophis capensis (Kaup, 1856). Collection of these specimens confirms the suggestion made from previous larval studies that spawning, development, and at least early larval growth of this species occurs in late summer in this area.
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- Date Issued: 1969-03
Two remarkable eel-larvae from off Southern Africa
- Authors: Castle, P H J (Peter Henry John) , Rhodes University. Department of Ichthyology
- Date: 1967-08
- Subjects: Eels , Fishes -- Larvae , Marine fishes -- Africa, Southern
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/69251 , vital:29465 , Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB)) Periodicals Margaret Smith Library (South African Institute for Aquatic Biodiversity (SAIAB))
- Description: Online version of original print edition of the Special Publication of the Rhodes University, Department of Ichthyology, No.1 , Ascomana gen. nov., based on A. eximia sp. nov. is described from a single 700mm leptocephalus collected off Cape Town. It displays the following characters which in combination distinguish it from known eel genera: — Jaws moderately produced, hyomandibula essentialy vertical, short postocular region, occipital crest present, slender upwardly-curved lower jaw, pectoral fin with very numerous rays (23-24); larva reaching at least 700mm, eye not telescopic, caudal not attenuated or rounded, very numerous teeth, intestine a straight tube, pigment mainly as a series of large melanophores along the ventral body wall from throat to vent. The new genus and species shows some resemblances to the nessorhamphid eels. An elongate (565mm) leptocephalus, also collected from off Cape Town (that is, in the locality of the Dana "giant" eel-larvae), is identified with Leptocephalus giganteus Castle and is the second undoubted specimen of this species.
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- Date Issued: 1967-08