Table 10. — Table of means for the significant 

 effects of temperature on standard length 

 after 15, 30, and 45 days of exposure. The 

 mean standard length at day was 11.98 mm. 



**Significant at 1-percent level. 



an area of gradually increasing temperature, 

 we might expect the fish to have accelerated 

 growth rates; however, temperature elevations 

 in the summer might exceed the tolerance 

 limit for a given species. 



The finding that salinity itself did not exert 

 a significant influence on growth does not agree 

 with the results of others who have found that 

 increased salinities increased the growth rate 

 of the guppy, Lebistes reticulatus , and various 

 salmonids. In these studies, however, fresh 

 water was used for comparison of salinity 

 effect and these effects were observed over 

 a longer period of time which may account for 

 the disparity of results. Others have shown 

 that the weight of postlarval summier flounder, 

 Paralichthys dentatus, and southern flounder, 

 P. lethostigma , tended to increase with in- 

 creasing salinity. For pinfish, salinity also 

 increased the relative size of certain body 

 parts significantly. Due to osmotic stress in 

 low-salinity water, it is possible that energy 

 arising from metabolism is being utilized by 

 the fish for maintenance and less energy is 

 available for growth. Salinity, in addition to 

 influencing growth, limits the distribution of 

 fish, and modifies the response of estuarine 

 organisms to ionizing radiation. 



Fish exposed to the lowest level of radiation 

 were slightly longer and had greater body 

 depths than unirradiated fish or those exposed 

 to higher levels of radiation. Such a finding 

 suggests a stimulation of growth by radiation. 

 Similar effects have been suggested from ex- 

 periments with salmon and have been den-ion- 

 strated in the blue crab, Callinectes sapidus . 

 The fact that, at 15° C, the radiation and tem- 

 perature interaction produced a heavier and 

 deeper bodied fish with relatively longer body 

 parts as radiation levels increased also sug- 

 gests stimulation. If the stimulation of growth 

 is real and can be reproduced, this combina- 

 tion of environmental factors might be used in 

 aquaculture. Low radiation levels would be 

 relatively easy to produce from a small cobalt 

 60 source suspended above a body of water. 



The temperature level of 15° C. also would be 

 easy to produce in the winter by proper use of 

 power plant effluent. Postlarval pinfish caught 

 and placed in a holding pond of sufficient size 

 under these conditions should grow at a faster 

 rate than normal. If the postlarvae of winter- 

 spawning fish of commercial value also show 

 stimulation in growth from low levels of chronic 

 radiation under specified environmental condi- 

 tions, marine fish farming on a commercial 

 scale might be feasible. Further study along 

 these lines is needed. 



Changes in the relative growth of various 

 body parts with respect to standard length 

 caused by radiation, salinity, temperature, 

 and their interactions could lead to a wide 

 variation in the final relative size of these 

 parts. Since the identification of many species 

 of fish depends on the relative size of certain 

 body parts, it is conceivable that the addition 

 of radioactivity and thermal loading in the 

 environment could lead to taxonomic problems. 



The genetic effects of low-level chronic 

 irradiation in the estuary on future generations 

 of fish may be the most important considera- 

 tion. Genetic materials in the developing gonad 

 are very susceptible to ionizing radiation and 

 may undergo mutations that would not appear 

 Tint il the Fj or later generations. The mutations 

 could lead to a stronger or weaker population 

 of fish, depending on the nature of the nnutation. 

 Changes in life span, reproductive capacity, 

 resistance to disease, and tolerance to environ- 

 mental changes of the irradiated population or 

 their progeny are distinct possibilities also. 



The subjects of chronic irradiation and 

 thermal loading and their combined effects on 

 estuarine populations clearly require far nnore 

 attention than they have received. Of probable 

 equal importance is a need for studies of the 

 potentially beneficial effects that might be 

 derived by manipulating these environmental 

 factors. It should be reemphasized, however, 

 that inhabitants of the estuary are not con- 

 trolled by any single factor. Although one fac- 

 tor, such as temperature, may by itself affect 

 the growth of an animal; another factor, such 

 as salinity or radiation, may be either syner- 

 gistic or antagonistic in its interaction with 

 temperature. Awareness is growing that as 

 many variables as possible need to be studied 

 simultaneously to understand and take advan- 

 tage of the effects of man's influence on the fu- 

 ture estuarine environment and its inhabitants. 



INTERACTION OF GAMMA IRRADIATION 



AND SALINITY ON RESPIRATION OF 



BRINE SHRIMP NAUPLU 



Joseph W. Angelovic and David W, Engel 



Ionizing radiation and salinity both influence 

 the physiological activity of marine species. 

 Although the effects of these factors have fre- 

 quently been tested individually on organisms. 



47 



