Mangroves and Salt Marshes 2: 177–185, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands. 177 Variations in condition and body constitution in a tropical estuarine fish with year-round recruitment Brett W. Molony and Marcus J. Sheaves Department of Marine Biology, James Cook University of North Queensland, Townsville, Q.4811, Australia (Received 17March 1998; accepted 16 June 1998) Key words: Ambassis vachelli, Australia, carbohydrate, estuary, lipid, protein Abstract Fish condition (Fulton’s K) and the abundance of biochemical constituents (water, protein, lipid and carbohydrate) of juveniles of the tropical estuarine fish, Ambassis vachelli, were monitored over a 15 month period. Fulton’s K and biochemical constituents of juveniles recruiting into the adult habitat varied significantly throughout the study. Correlations between Fulton’s K and all biochemical measures were weak, with a maximum correlation of 0.1379 (with protein abundance). Significant differences in condition and body constitution of individuals suggest that juveniles recruiting into the adult habitat are not in equal condition and therefore survivorship and success may vary within and among cohorts. Temperature (and salinity) display greater variation in tropical estuarine waters than in other tropical waters and are likely to play a role in determining recruit condition and body constitution. However, the exact role of physical parameters in determining condition and body constitution of fishes is still unknown. Introduction The recruitment of larval and juvenile fishes into adult habitats has been a major focus in fisheries and bi- ological research. Recently, research has shown that there is considerable variations in the condition of re- cruits that enter a habitat. For example, McCormick and Molony (1992, 1993) found that condition of the goatfish, Upeneus tragula, recruiting to tropical reefs varied considerably (in terms of size, age and body constitution) over the recruitment season. Ker- rigan (1996) found similar results in recruits of the tropical damselfishes, Pomacentrus ambionensis and P. nagasakiensis. Although significant variations in condition (measured as Fulton’s K and the abundance of lipid, carbohydrate, water and protein abundances) were recorded, the range of environmental conditions that recruits experienced over the recruitment period were relatively modest. For example, McCormick and Molony (1995) determined that the temperature pelagic U. tragula larvae were exposed to prior to settlement varied approximately 5 ◦ C over the recruit- ment season (approximately 4 months). Although this range of temperature induced a range in condition and abundances of body constituents in recruiting lar- vae (McCormick and Molony, 1995), a temperature range of 5 ◦ C is relatively minor when compared to other tropical marine systems, such as mangrove-lined estuaries. In mangrove-lined estuarine systems of northern Australia, distinct seasonality results in rainfall being concentrated over several months of the year, with a majority of the year being relatively dry. Data from local collections indicates that rainfall, water tempera- ture and salinity vary dramatically over a tropical year (Figure 1), much more dramatically than in reef areas (e.g. McCormick and Molony, 1995). Therefore, an- imals recruiting to tropical mangrove-lined estuaries are likely to be exposed to a wider range of tempera- tures and salinities (Molony, 1993) and are therefore expected to display a wide range of characteristics (condition and constituent abundances). An ideal organisms to test this hypothesis on is the tropical estuarine glassfish, Ambassis vachelli Richardson. Ambassid fishes are almost cosmopoli- tan in tropical, mangrove-lined estuarine systems of mang42.tex; 23/11/1998; 8:31; p.1 MENNEN/SCHRIKS:DISK/CP: Pips Nr.:184657; Ordernr.:232252-mc (mangkap:bio2fam) v.1.1