REARING TILAPIA FOR TUNA BAIT 



Tabi.k 6. — Conccntiatioiin (ml. /I.) of disnolrrd oxiigoi at 

 different drptUx and i)Oiiition,<i in brood tankx, lO/iS 



Sampling time and depth 



Tank A ' 

 0815 hours: 



Surface.-- -.. 



Midway 



Bottom -- 



1330 hours: 



Surface 



Midway --- 



Bottom 



Tank B = 



0830 hours: 



Surface 



Midway- 



Bottom 



1315 hours: 



Surface--- 



Midway - 



Bottom--- 



Outlet 

 end (NE.) 



0.53 

 .52 

 .42 



2.54 

 2.39 

 2.43 



.73 



4.17 

 3.60 

 3.49 



Middle 



0.70 

 .47 

 .40 



3.31 

 3.29 

 3.26 



.51 



.47 

 .48 



3.50 

 3.42 

 3.47 



Inflow 



end (SW.) 



0.76 

 .70 

 .66 



3.46 

 2 99 

 2.97 



.34 

 .32 



.18 



2.99 

 2.33 

 2.18 



1 Sampled March 4. 

 - Sampled March 5. 



7.9.5.9. — In 1959, in contrast witli 1958, oxyfren 

 concentrations in the brood tanks were nsually fa- 

 vorable following: installation of the aeration sys- 

 tem, with very few readinojs below 1 milliliter per 

 liter and with the average above ?> ml. /I. The 

 very low levels in concentrations of oxygen in some 



Table 7. — Measiironiciits (ml./l.) of dissolved oxypen in 

 selected tanks, taken atjout midday, 1959 



of the fry tanks, however, may have lieeii caused 

 by retention of tish for long periods of time in a 

 single tank with inadefiuate flnshiiig. The o.xygen 

 concentrations in tlie brood tanks and in selected 

 fry tanks are given in table 7. 



Other Chemical Determinations 



Several cliemical determinations were made in 

 1959 in addition to the oxygen measnremenfs. 

 Data on hydrogen ion concentration (pll), and 

 carbon dioxide (CO2), bicarbonate (HCO:,), and 

 normal carbonate (CO3'') concentrations are pre- 

 sented in table 8. The slight differences in the pH 

 concentrations in the two brood tanks were judged 

 to be negligible. The (X),, C03=, and HCO:, con- 

 centrations are approximations, since it was dif- 

 ficult to determine the end points when the water 

 samples were dirty brown to deep green in color, 

 as was frequently the case. 



T.VBLE S. — Chemical determinations made on tirood tanks, 

 J9.39 



