Aspects of the biology of the doublesash butterflyfish, Chaetodon marleyi (Pisces : Chaetodontidae)
The doublesash butterflyfish, Chaetodon marleyi, indigenous to South Africa, is popular amongst marine aquarists. To provide a basis for the management of the species and assess its suitability for aquaculture, aspects of its biology were investigated. Specimens were collected between February 1996 and November 1997 from localities along the eastern Cape coastline of South Africa and from specimens in the RUSI fish collection.
The dentition of C. marleyi is typical of non-coraline, benthic invertebrate feeding chaetodontids. The teeth are long, inwardly hooked and spatulate which allow easy grasping and manipulation of the prey. Stomach content analysis showed that the species fed predominantly on the tentacles of terebellid polychaetes with other polychaetes, crustaceans, hydroids and ascideans contributing to the remainder of the diet. Juveniles had a larger volume of terebellid tentacles compared to adults which preyed more upon other polychaetes. The proximate composition (64.25% protein, 4.76% fat, 4.84% carbohydrate and 24.3 kJ/g total energy content) of the terebellid tentacles was determined suggesting a high energetic requirement of the fish or maximisation of feeding profit rates.
Growth in C. marleyi is rapid and was described by the von Bertalanffy growth equation as L(t) = 179(1-e[superscript (-021(t+1.42))])) using a combination of daily increment analysis and annual ring counts obtained from sectioned sagittal otoliths. Length-frequency analysis revealed six cohorts.
Investigations into the reproductive biology indicated that the species is a gonochorist. Sexual development in males was evident in fish ?56 mm TL and ?63 mm TL in females. Males mature at approximately 105 min TL or two years of age. Reproductive activity in males peaks between May and November with females releasing multiple batches of pelagic eggs during the spawning period. Birthdates, obtained by backcalculation of daily increment data from the time of capture, indicated that hatching occurs in late winter and spring.
Life history characteristics of the species include rapid growth, early maturity and relatively short life-span. Due to the importance of C.marleyi in the local marine ornamental fishery various management options should be considered. The absence of any reproductively active females along the eastern Cape coastline may indicate that larval recruitment occurs from KwaZulu/Natal. Other possible management options include a closed season during summer, the period of juvenile settlement; a slot size limit to protect small juveniles and mature adults, and; a bag limit of two fish per person.
Although the rapid growth and early age of reproductive maturity of C.marleyi are desired traits of a candidate aquaculture species, the long larval period may currently prove too problematic for the farming of the species.
School Location:South Africa
Source Type:Master's Thesis
Keywords:ichthyology fisheries science
Date of Publication:01/01/1998