Davis and West: Reproductive biology of Lutjanus vittus from North West Shelf of Australia 



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29 4 8 12 16 20 24 28 

 Moon age (days) 



Figure 7 



Proportion of mature female Lutjanus vittus with early- 

 or late-stage postovulatory follicles plotted against time of 

 sampling (expressed as moon age). A sinusoidal curve with 

 a period of 29 d and two peaks of unequal height were fit 

 to arcsine (angular) root-transformed data. Lunar tide 

 cycle, indicated by maximum and minimum heights of 

 daily tides, has also been plotted, and the number in each 

 sample is shown. 



F= 124.2 x W-3081 (F=17.7, df l,27,p<0.001). 



Batch fecundity varied markedly between fish of the 

 same size. As the data were obtained from four differ- 

 ent periods during the spawning season, we tested to 

 see whether the different spawning periods could ex- 

 plain some of the variability in batch fecundity. There 

 is some suggestion that batch fecundity might be higher 

 in November and decline over the spawning season, 

 following the seasonal pattern of RGI (Fig. 11). How- 

 ever, in the regression of log fecundity/log length, the 

 test for homogeneity of slopes between sampling peri- 

 ods was found to be not significant ( ANCOVA, F=0.318, 

 df 1,2604, p=0.57), and, assuming a common slope, 

 there was no significant difference in the intercepts 

 for the four periods (ANCOVA, F=1.76, df 1,2605, 

 p=0.19>. 



Oven-dried weights of hydrated oocytes were deter- 

 mined on 9 fish. Egg weight did not vary with fish 

 length (F=0.28, df 1,8, p=0.61) or with maximum oo- 

 cyte diameter (F=0.88, df 1,8, p=0.37). The mean dry 

 weight of individual hydrated oocytes was 0.012 mg 

 (SE 0.0005). 



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4:00 8:00 12:00 16:00 20:00 24:00 



Time of day 



Figure 8 



Proportion of mature female Lutjanus vittus with ripe-stage 

 ovaries, and maximum oocyte diameter (MOD) in individuals 

 caught at different times of the day. Samples taken during 

 periods of major spawning activity (lunar days 2-10 and 18— 

 29) during November-December 1982. Oocytes have been as- 

 signed to ovarian maturity stages: Ripe ( ) and Yolked (•). 

 Shown are 95% binomial confidence limits for proportions 

 and number in each sample. 



Discussion 



The smallest ripe female observed in this study was 

 142 mm long, which is close to the length-at-first- 

 maturity of female L. vittus from New Caledonia 

 (Loubens 1980a). In a review of size-at-first-maturity, 

 Grimes (1987) found consistent differences between in- 

 sular and continental species of lutjanids and between 

 shallow and deepwater groups in the ratio of length- 

 at-first-maturity to maximum length. Female L. vittus 

 clearly fall into the continental shallow group that ma- 

 ture early at -44% of their maximum length. 



The spawning season on the NW Shelf is pro- 

 tracted: While L. vittus spawned throughout the year, 

 the major spawning period appeared to be September- 

 April. Loubens (1980a) determined from GSI and 

 visual staging that L. vittus spawn during October- 

 February in New Caledonia (Loubens 1980a). Lutjanus 



