The playful behaviour of laboratory rats (Rattus norvegicus) was investigated in litters of five individuals with the mother present; parallel observations were made on mice (Mus musculus). Seven mixed litters containing four young rats and a young mouse fostered at birth were also observed. Solitary play was recorded in both species and took a similar form but social play was only observed in rats. In rats, solitary play frequently preceeded social play. The behavioural elements involved in the social play of Rattus norvegicus were described, and the majority of these were the playful equivalent of adult agonistic behaviour elements. These social play elements were found to be organized into definite sequences which differed from those of adult aggression. Each behavioural element was found to act as a social releaser. Young mice did not respond playfully to social play from a rat litter mate; mice were less attractive to rats as playmates in comparison with fellow rats.

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18 C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2·8 to 15·9 g. A predictive model for the maximum meal size (M max ) at temperatures between 10 and 18 C, accounted for 95% of the variance in lnM max . Even when offered excess food, bass at 6 C had a low rate of food consumption [0·19% body weight (BW) day 1 ] and lost weight (G= 0·04% day 1 ). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0·7 and 2·3% BW day 1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18 C optimum ration was 7·4% BW day 1 . At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17·4% at 18 C. Mean absorption efficiency was 94·8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6 C. Condition indices (Fulton condition factor, wet and dry liver-somatic indices and body depth index) increased with meal size at all temperatures except 6 C. An increase in temperature between 10 and 18 C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature. 1996 The Fisheries Society of the British Isles

This article is part of a series describing the development of the Spray Drift Task Force (SDTF) database and its application to agricultural chemical exposure risk assessment modeling. The series describes the development of a large generic database (assuming that active ingredient rate is not a factor affecting physical drift) and its use in estimating spray movement immediately following application by aerial methods. The components of the database are described. In agreement with field trials in the open literature, the database shows that the major variables affecting off-target spray deposition are droplet size, spray release position (boom height and length), and wind speed and direction. In addition, secondary parameters that can affect these variables and drift are also discussed.

Hydrobia ulvae has featured in many reports on the ecology of estuaries and mud-flats, yet surprisingly there are few detailed studies on population structure, growth and the breeding cycle. Population densities fluctuate widely from one locality to the next, and the variation in size recorded for the adults suggests significant differences in growth rate and the size at which the snails become sexually mature. The occurrence of Hydrobia in the stomachs offish and birds is well documented (Clay, 1960) and the suggestion that this species may influence the breeding success of some species of bird (Anderson, 1971) illustrates its importance in the ecology of estuaries and salt marshes.

Eight litters of Rattus norvegicus of the PVG/C hooded strain were observed in order to investigate the roles of individuality, sexuality and age in playful behaviour. Three measures of social play, namely, initiations, numbers of play bouts and numbers of playful elements performed were all found to be positively correlated. The incidence of social and solitary play were also positively correlated so that a concept of “playfulness” appeared to be justifiable. Playfulness showed no correlation with the general level of non‐playful locomotor activity. Male rats were more playful than females but only minor sex‐related differences were found to occur in the sequential organisation of play. Older rats showed longer play bouts and a higher degree of temporal organisation. Considerable individual differences in playfulness were recorded and in single sex litters playful rats were found to play together. The majority of opponents, in playfighting, alternated between the roles of attacker and defender.