Filial cannibalism in the swordtail Xiphophorus helleri (Poeciliidae) C.L.W. Jones, H. Kaiser  , G.A. Webb and T. Hecht Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94 Grahamstown 6140, South Africa To understand behaviour during ®lial cannibalism in swordtails ( Xiphophorus helleri ), the parturition behaviour of eight individually kept females was recorded on videotape. Three levels of female activity (low, medium and high) were quanti®ed by measuring the duration of each. Four additional behavioural events (non-cannibalistic feeding, as well as the birth, attack and cannibalism of juveniles) were quanti®ed by determining the frequency of each. Females gave birth most frequently at a low level of activity and at this level of activity they most often gave birth at the top of the tank. Of all the attacks by females on the young, 84.4% occurred in the light. Most attacks were recorded at the bottom of the tank and 84.0% of all cannibalism occurred at the bottom. Cannibalism was most successful at the bottom of the tank with a cannibalism:attack ratio of 1:2.2 and least successful in the middle where no cannibalism was recorded. In the light, females spent more time at the top of the tank, whereas in the dark they spent more time at the bottom. It was suggested that the rate of cannibalism might be reduced if parts of the tank were kept constantly dark and if females were restricted from reaching those areas in the tank where the frequency of cannibalism was highest, namely the top and the bottom of the tank. Experimental designs and working hypotheses for future studies are discussed. KEYWORDS: aquarium design, ®lial cannibalism, photoperiod, swordtails, Xiphophorus helleri INTRODUCTION Live-bearing ®sh of the family Poeciliidae form an important part of the international aquarium ®sh industry. One problem associated with intensive production of these ®sh is ®lial cannibalism (Kruger, 1995; Jones et al., 1998). Short of direct observation, there is suf®cient evidence to suggest that cannibalism occurs in the swordtail Xiphophorus helleri (Jones et al., 1998). In an experiment designed to quantify the rate of cannibalism in X. helleri, where the broodstock was kept under conditions comparable to those of commercial operations in South Africa, it was found that 34:4  5:3% (mean  standard error) of the expected number of juveniles were cannibalized by the adult ®sh (Jones et al., 1998). The behaviour of the adult broodstock as well as that of the juveniles during the parturition period (the time period between the ®rst and last birth) has Aquarium Sciences and Conservation, 2, 79±88 (1998) 1357±5325 # 1998 Chapman & Hall  Author to whom correspondence should be addressed (e-mail: ihhk@warthog.ru.ac.za)