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

64 CALIFORNIA COOPERATIVE OCEBNIC FISHERIES IPU'VESTIGATIOhTSto the influence of mechanical factors. This sensitivityis at its peak in the earliest stages of development,including early gastrulation. In view of this fact thepresent author believes that high seas and stormsmight have some influence upon the fate of anchovyembryos which are, at the time, in this stage ofdevelopment.Growth, Age, Condition Factor, and MetabolismThe Argentine anchovy is a fish of short life thatreaches its sexual maturity and becomes already asubject of commercial fishing at the age of one year.The problems concerning its growth, age, conditionfactor and metabolism were studied by Fuster dePlaza (1964). The results obtained by the sameworker are based upon a statistical elaboration ofdata, applying the method of Petersen. According toFuster de Plaza, the distribution of the samples inmodal classes through time show the existence of twopopulations of anchovy ; the spring and autumn populations,with their corresponding growth parameters.Both populations show an active growth until the endof the third year of life. From then on, growth decayssensibly. The calculated length at the fourth year oflife is 185 mm for the spring anchovy, and 175 mmfor the autumn anchovy. Growth is halted in bothpopulations during the winter months. According toFuster de Plaza, the total lengths of the anchovy duringthe first 4 years of life are as shown in Table 2(Petersen Method).TABLE 2MODAL CLASSES IN MM11 12 1s 14Spring population ---___--- 130Autumn population ---_---- 110150135375 165185175Little is known about the growth of the anchovy inits first stages of life. In a paper currently in press,the present author shows that the analysis of themonthly distribution of length frequencies of larvaeand juveniles, taking into consideration the first momentsof intensive spawning, seems to indicate thatthe juveniles of anchovy reach a length of 60 mmwhen they are in the third month of life.According to Fuster de Plaza, the rate of weightincrease in the adult anchovy is greater than the rateof length increase, and the development of the bodytakes place in a more or less harmonious manner alongthe three body axes. Also, the value of the Conditionfactor K shows a progressive increase with the growthof the individuals. For adult individuals in the opensea, during their period of intense nutrition, thisfactor is of 0.70 to 0.90, whereas for juveniles individualsin coastal waters, the same factor ranges from0.50 to 0.73.The degree of fatty accumulation in the viscerae ofthe anchovy is related to the stage of development ofthe sexual glands. The greater deposits of fat arefound in anchovies which have gone through thereproductive process and are in a state of repose.Fuster de Plaza has determined also the metabolicspecific factor k, following criteria due to Bertalanffy,who considered the metabolism of fishes to be proportionalto body surface. The average value of thisfactor for the anchovy is 8.75. It also appears thatthere is no sensible decline of the metabolic rate withthe increase of the length.FeedingThe present author has undertaken studies of thefood and feeding habits of larvae and juveniles ofanchovy. The characteristics of the alimentation atdifferent developmental stages have been related tothe morphological changes taking place throughoutthe development of the individual. The first results(not yet published) show that the anchovy larvaewhich are 3-5 mm long (that is, after reabsorptionof the vitellus) feed almost exclusively on the eggsand nauplii of Copepoda, and small eggs from otherorganisms. In larvae from 5 mm to 35 mm long, ithas been impossible at the present to find remnantsof food. This should be due to the structure of thedigestive tract, which in this stage of development islike a straight tube, with a slight ketch of stomachin the greater larvae. From the length of 35 mm on,the percentage of individuals in whose intestines foodis found, becomes higher.The basic food for individuals from 35-80 mm longare Copepoda in all stages of development: eggs,nauplii and adult forms. Besides Copepoda, there arealso to be found juveniles of Decapoda and otherCrustacea, eggs from various marine organisms andmore rarely, larvae from fishes and Mollusca. In thefood of juveniles from 40 mm long are found Radiolaria,and Acantharia, but in scarce amounts. In thefood of juveniles with a length of more than 50 mmthere appear Diatomea and Dinoflagellata, alwayswith other zooplanktonic forms.Fuster de Plaza (1964) and Fuster de Plaza andAngelescu (1962) obtained somewhat different resultswith respect to the alimentation of the juveniles ofanchovy. They found their food to be primarily composedof phytoplankton. In individuals from 50 mmto 100 mm long in the primarily phytoplanktonic food,they found a predominance of Diatomea. As the juvenilesapproach the adult stage, the alimentation becomespreferentially zooplanktonic.According to said authors in the food of individualsfrom 150-190 mm long, there are Copepoda, especiallyfrom the family Calanidae, pelagic Amphipodae (Parathemistospp.), Sergestidae (Xergestes spp.) and sometimesjuveniles of anchovies and other fishes.The anchovy is plainly a plankton feeding speciesand is located in a low trophic level, near the primaryproduction link.MigrationsAlthough many data are lacking for a precise determinationof the population dynamics of the anchovy,it is possible with the available data to reachsome conclusions on the migration of large schools ofanchovies in the area of the Province of Buenos Aires.As was shown in the preceding sections, the migrationsof the anchovy are both trophic and reproductivein character. On this matter there are data published