> tapply(wtgain,list(temp,density,saline),mean)
, , 10

          80       160
25  70.33333  70.66667
35 408.00000 331.00000

, , 25

         80      160
25 465.6667 333.0000
35 274.6667 311.6667

, , 40

    80      160
25 359 252.3333
35 243 230.6667

> tapply(wtgain,list(temp,density),mean)
         80      160
25 298.3333 218.6667
35 308.5556 291.1111
> tapply(wtgain,list(temp,saline),mean)
      10       25       40
25  70.5 399.3333 305.6667
35 369.5 293.1667 236.8333
> tapply(wtgain,list(density,saline),mean)
          10       25    40
80  239.1667 370.1667 301.0
160 200.8333 322.3333 241.5
> 
> shrimp.mod1 <- aov(wtgain ~ temp*saline*density)
> summary(shrimp.mod1)
                    Df Sum Sq Mean Sq F value    Pr(>F)    
temp                 1  15376   15376  5.2952   0.03038 *  
saline               2  96763   48381 16.6615 2.901e-05 ***
density              1  21219   21219  7.3073   0.01242 *  
temp:saline          2 300855  150428 51.8041 1.959e-09 ***
temp:density         1   8711    8711  2.9999   0.09610 .  
saline:density       2    674     337  0.1161   0.89086    
temp:saline:density  2  24038   12019  4.1392   0.02855 *  
Residuals           24  69691    2904                      
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
> 
>