This study compared three methods used to measure aggression in the male three-spined stickleback. These methods have been used in different studies without the certainty that they measure the same behavioural phenomenon. A number of different measures of aggression must be highly correlated if aggression in the male stickleback is to be regarded as a unitary drive. The methods consisted of recording the behaviour of an experimental male when: (i) a tube containing another male (or a female in some tests) was visible for 5 min; (ii) another male was visible across a glass partition at all times; (iii) a fish-shaped wax model was visible for 2 min. Each method showed that in the 12 days after fertilization of an egg-mass, there was a U-shaped trend in frequency of biting, frequency of charging and the rate of biting per minute spent oriented towards the other fish or the model. In Method (i), total oriented time formed about 70 % of a test period and this measure was not correlated with frequency of biting, nor did it follow a U-shaped trend. In Methods (ii) and (iii), total oriented time formed less than 50 % of a test period, was correlated with frequency of biting, and did follow a U-shaped trend. In Methods (i) and (ii), the measures, frequency of biting and bites per min of oriented time were at a maximum in the first 15 min after fertilization. Method (iii) did not show this maximum in biting. All methods showed that frequency of biting, of charging, and bites per min of oriented time were higher for fish with nests than for fish which had yet to build nests. Gonadectomy of fish with nests reduced all measures to the levels found for intact fish that did not have nests. An experiment using only Method (i) showed that a male with a nest attacked another male more than a non-gravid female. A male without a nest attacked both a male and a non-gravid female equally. The use of more than one measure for a behaviour pattern improved both the comparisons between methods and the analysis of changes in behaviour of the male. Examples of this are given for biting and parental fanning. Results from Method (iii) were not always consistent with those from Methods (i) and (ii). Method (iii) was exceptional in the number of charges the experimental males made with both dorsal and ventral spines erect. A wider range of behaviour patterns were recorded more regularly in Method (ii) than in Method (i). But these two methods consistently showed the same trends in frequency of biting, charging and bites per min of oriented time. In spite of the similarities in the results from the three methods there was not sufficient evidence to conclude that aggression in the male stickleback is a unitary drive and that all potential measures of aggression will be equivalent. / Science, Faculty of / Zoology, Department of / Graduate