FileList Convert a pdf file! Koedoe 19: 43-48 (1976) SEX REVERSAL IN THE DAGERAAD CHRYSOBLEPHUS CRISTICEPS (PISCES, SPARIDAE) C . A. ROBINSON Tsitsikama Coastal National Park P.O . Stormsrivier 6308 Abstract - This paper reports protogynous hermaphroditism in the dageraad Chrysoblephus cristiceps. Mass-length relation- ships indicate growth changes in male and female fish . Sea- sonal maturity in dageraad, and hermaphroditism in South Afrit:an spari where L = length in millimeters a = intercept of the y axis W = mass in milligrams b = exponent Logarithmic transformations yield a linear relationship from which a and b can be calculated by the method ofleast-squares. ... '" ~ z 100~--------------~~--------------~~----------------~ 75r----------1~--------~------~------_*--------------~ ~ ~~--------~------------~--~----------~~----------~ II: ... ... 25r--------.~-------------.~._--------------~._------~ 11 ZI .. zt II n " .5 '0 l LENGTH Cem) Fig. I. Size composition of a Dageraad population as obtained from hand- line catches in Tsitsikama Coastal National Park. 44 Results (i) By plotting the relative frequency of the size groups it is clearly seen that sex reversal is taking place (Fig. 1). The majority seem to undergo this sex change during the lengths 33-37 em (caudal length), although there are some of both sexes between 29 and 41 em due to differential growth rates. The mode of the female individuals in the population, peaks at 26-30 em whereas the male individuals in the populations peak at 39-43 centimeter. The con- clusion is that Chrysoblephus cristiceps is protogynous hermaphro- ditic. (ii) The mass-length relationships were calculated: W = 0,0324 U·877 W = 0,0052 U·m It can be seen from Fig. 2 that in the smaller female fish this rela- tionship is curvi-linear whereas in the larger, male fish, this reia- tionship is linear i.e. growth changes between sexes. (iii) By grouping all the maturity index data by month, as inactive (maturity indices 1 and 2) and active (maturity indices 3 to 7), the relative proportion of active to inactive indicates a peak activity in November and a minimum in July-August, suggesting a spawning period in October to December (Fig. 3). Discussion Chan ( 1970) reviewed the phenomenon of sex reversal found in verte- brates and concluded that sexuality in these animals may be classified into two main groups i.e. gonochorism and hermaphroditism . He notes that in the sparids there exists a diversified expression of sexuality and hermaphroditism. The basic structure of the gonads of sparids are re- ported to consist of a paired ovotestes fused posteriorly while the cavities of the two lobes form a common duct. Internally each lobe consists of ovarium lamellae, where ovarium follicles develop and mature. Poste- riorly on the ventro-Iateral part of each lobe, testicular tissues are visible as two bands adjacent to the lumen of the gonad with connective tissue separating male and female zones. Macroscopically the development of the testicular part were seen to develop on the ventrolateral portion of the gonads in Chrysoblephus cristiceps as well as the roman Chrysoblephus laticeps and another sparid, the red steenbras Petrus rupestris. This latter species was reported by Penrith (1972) to be bisexual or gonochoristic. The evolution of hermaphrodit- ism is extremely scanty but it is obvious that simultaneous hermaphro- ditism would be a disadvantage due to the possibility of self-fertiliza- tion and inbreeding. However, protogynous hermaphrodites could provide a mechanism as good as gonochorists. ' Penrith (1972) presents an intriguing theory for the presence of pro- 45 E - ~OM~----------------------------~~------~ fI) w .... ~ z: UI ... ~ Fig. 2. 10 .to 50 fI) w .... ooC 2 w "" ooC 2 Mass-length relationships for Chrysoblephus cristiceps 00 and 99· togynous hermaphroditism in Chrysoblephus laticeps. He believes that this fish with its large heavy head, flabby body, and soft slightly concave caudal fin, becomes hydrodynamically a poorer swimmer as it increases in size. The advantage of sex reversal being that the younger reproduc- tive sector of the population could avoid their natural predators, while the larger slower males would have the potential of fertilizing several 46 . , , • , '0 II , 2. I' I. a + Fig. 3. Monthly relative frequency of maturity indices 3 to 7 fish in the popu- lation. females. In this way survival of the species under natural conditions is guaranteed. Chrysoblephus cristiceps is similar in body dimensions to ChTysoblephus laticeps and is therefore also prone to becoming a poorer swimmer as it increases with size and age. Dageraad were relatively abundant along the south coast between Cape Point and Algoa Bay but their numbers and size in catches have decreased rapidly during recent times. F. Spalmer (peTs . comm.) noted that at Arniston this change has been most dramatic, whereas the fisher- men caught many, large dageraad they now return with fewer and smaller fish. The Tsitsikama coast is treacherous and the population of dageraad have not been exposed to the same pressure of exploitation as other areas along the coast. It is suggested that the reason for good catches still to be obtained at Tsitsikama, is due to the protection these fish are afforded in the Park. At present the conservation of this species is based on a minimum length size of 20 centimeters. It is proposed that due to the protogynous hermaphroditic nature of dageraad that a regulatory measure be imposed on the maximum size and that all fish over 40 cm (LC) should be released when caught. (A similar regulation exists in the case of the lobsters along the northwestern shore of America). 47 A cknowledgemenls I would like to extend my thanks to Messrs. T. Dearlove, D. F. Bower, J. A. Fourie, P. van Rooyen, P. Scott and P. Ngubu for assisting in the catching and recording of these fish. REFERENCES CHAN, S. T. H . 1970. Natural sex reversal in vertebrates. Phil. Trans . Roy . Sqc. Lond. B. 259 :59-71. LUCKS, D. K. 1970. Aspekte van die Biologie van die witsteenbras (Lilhognalhus aureli Smith, 1962) in die Sandwichhawe-strandmeer. M .Sc. Thesis, University of Stellenbosch. (Unpublished). MEHL, J. A. P. 1974. Ecology, Osmoregulation-and Reproductive Bio- logy of the White Steenbras, Lithognathus lithognalhus (Teleostei: Sparidae). Zool. afro 8(2): 157-230. PENRITH, M. J. 1972. Sex reversal in the sparid fish Chrysoblephus laliceps. Koedoe 15: 135-139. 48 Page 1 Page 2 Page 3 Page 4 Page 5 Page 6