CalCOFI Reports, Vol. 11, 1967 - California Cooperative Oceanic ...

INFLUENCE OF SOME ENVIRONMENTAL FACTORS UPON THE EMBRYONICDEVELOPMENT OF THE ARGENTINE ANCHOVYENGRAULIS ANCHOITA (HUBBS, MARINI)'JANINA DL. DE CIECHOMSKIlnstituto de Biologia MarinaMar del Plata, Casilla de Correo 175, ArgentinaAn extensive literature exists on the problem of theinfluence exerted by several environmental factorsupon the early stages of development in fishes. Otherworkers have dealt with this subject either from thepoint of view of obtaining a deeper knowledge of thebiology of the species under research, or from thestandpoint of solving some practical problems throughtheir studies. Thus the majority of these publicationsrefer to species of economical importance.The object of the present work was to study theinfluence exerted upon the embryonic development ofthe Argentine anchovy Engraulis anchoita by thefollowing environmental conditions : temperature, salinity,light, and mechanical factors. Special attentionwas given to the temperature, since this factor undergoesgreater changes during the spawning period ofthe anchovy. The reproductive season of this species isquite long (Dz. de Ciechomski, 1965 ; Fuster de Plaza,1964), lasting for approximately 9 to 10 months,and therefore the temperature varies considerablythroughout this period. The investigation herein describedwas aimed at the determination of the developmentalrate at different temperatures, and at an establishmentof the optimal values and limits within whichthe embryonic development of the anchovy normallytakes place.In the case of salinity, an attempt was also made toestablish the limiting values within which the normalembryonic development of the anchovy could takeplace. It was also the aim of this research to obtainsalinity data in order to compare them with thevalues recorded for other related species of greatsalinity tolerance.In the case of light, it seemed to be of interest todetermine whether this factor exerts any influenceupon the embryonic development of the anchovy.Upon noting the great mechanical susceptibility ofthe eggs of Engraulis anchoita, it was considered ofinterest to study this phenomenon in detail. The investigationwas thus directed towards a determinationof the developmental stages of the embryo at whichthis susceptibility manifested itself with the greatestintensity. A study of this problem is of particularinterest since high seas and storms may have someinfluence upon the fate of anchovy embryos whichhappen to be in development under those circumstances.Rollefsen (1930), in his work on the cod, hasshown that intense wave movement does have an1This paper has been prepared through the sponsorship of theCouncil for Scientific and Technical Research of Argentina.effect on the embryonic eggs of fishes. According tothis worker, the years of very good catches werealways preceded by years of light winds and fineweather during the reproduction season of this species.MATERIALS AND METHODSAs basic material for the experiments, eggs obtainedby artificial fecundation as well as eggs collected fromplankton were used. Artificial fecundation was accomplishedusing the method usually employed tothis end. The eggs obtained from plankton wereselected so as to use those which were in early stagesof development, (Le., up to the beginning of theblastula stage).For the experiments concerning the influence oftemperature, the eggs obtained from artificial fecundationwere placed in different aquaria, some being keptwithin a temperature ranging from 19" to 20' C.,some within 14" to 15" and others at 4" C. Thetemperature of 19" to 20" C. was obtained by meansof a thermostat; the 4'C. by placing the aquariuminside a refrigerator, whilst the 14"-15" C. correspondedto the room temperature at that time. Fortechnical reasons, it was impossible to obtain temperaturesranging from 8" to 10' C.In the experiments made concerning salinity, thefollowing procedure was used : to obtain salinitieslower than normal, distilled water was added to thefiltered sea water; to obtain salinities higher thannormal, a suitable amount of sodium chloride wasadded. Experiments were made with the followingsalinity values: 3.9 %o; 8.4 %o; 16.8 %o; 25.2 %o; 33.520 ; 50 & and 60 %o.To study the influence of light, an aquarium containingeggs in development was kept in completedarkness, another one was kept under continual illumination,whilst a third was maintained with naturallight as a control.The study of the mechanical susceptibility of theembryos was made by submitting the embryos atdifferent stages of development to the effects of differentpressure, and of shocks resulting from their beingdropped from different heights. To study the pressurefactor, the eggs were placed between two slides, threeat a time, arranged so as to form a triangle. Progressivelylarger weights were then placed upon the slides.After each manipulation the eggs were examinedunder the microscope in order to determine the resistanceof the membrane and of the embryo. These