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

~table shows the values calculated for the volume andweight of some of the planktonic components.REPORTS VOLUAIE XI, 1 JULY 1963 TO 30 JUNE 1966 73TABLE 1WEIGHT OF SOME PLANKTONIC ORGANISMS MOST FREQUENTLYFOUND IN THE FOOD OF THE LARVAE AND JUVENILES OF1MARINE FISHESMean Hagmeier MeanOrganisms di:F volume coefficient weight(mm3)(mg)PeridineaEzuuiaello sp..----CopepodaCalanoida- ._._._. 1000" .~._. _._ 1000-2000" ........ 2000-3000" _._...__ 3000-4000" .~. 4000-5000-.. -Harpacticoida(Euterpina acnt.).Cyclopoida---. .DiatomeaCoseinodiseus spp.- 124 x 32Triceratium spp.. . 145 x 114 x 6(CladoceraEuadne nard .Larvae of Lamellibranch...........Anchovy eggs.. . . ..Fish eggs.. . . . . ~48 x 36480 x 850-._.356 x 176f240 x 130. 420-780200-3441370 x 72010000.0001600.0004960.00003250.01200.13300.45801.42804.00000.00950.00500.00920.00440.37800.52301.11.11.051.041.041.041.041.041.041.04(1.04)0.0001750.0005450.0000340.01250.13730.47141.48514.16000.01000.00520.0095..._ 0.0044_.__ 0.3780__.. 0.5230___Of course, these calculations are not free from error,especially in the case of the Copepoda, which havebeen classed by great groups and by size classes,instead of by separate species, which would havebeen more correct. In the present conditions, a morerefined treatment was not feasible.For the calculation of the ingestion coefficient thefood weight was divided by the weight of the individual,and the result was multiplied by 1,000.The measurements of the dimensions of the mouthwere made by means of the inicrometric eyepiece. Themouth was opened by means of very thin needles andthe length and width of the mouth were measuredunder approximately the same angle. The first branchialarch of the left side was used always for observingthe development of the gill-rakers.INCIDENCE OF FEEDINGThe incidence of feeding was remarkably low,especially in some of the size classes of larvae. InTable 2 the values for the incidence of feeding forlarvae of different lengths are shown.As is shown in Table 2, the incidence of feedingvaries greatly with the size of the larvae and juvenilesof the anchovy. It is relatively high for the larvaewhose lengths fall within the 3.0-4.01 mm class. Thelarvae in this group have just reabsorbed their yolkand have begun to feed themselves. While the growthof the larvae continues the incidence of feeding de-Length ofOrganism (mni)Number ofOrganismsIncidence ofFeeding3.0- 4.0 -...--..... 5652.24.0- 5.0 ._......... 4218.25.0- 9.0 .--.--..... 5009.0-20.0 ........... 1 3505.720.0-30.0 ..-.._..... 360 9.230.0-40.0 ........-..17.940.0-50.0 --..-...-.. I 57.350.0-90.0 ...........245 78.6Total ...........1705 larvae503-NumberIof organisms containing foodcreases sharply, reaching the value 0 for individuals inthe 5.0-9.0 mm class length. In those larvae whoselengths exceed 9.0 mm the incidence of feeding beginsto increase gradually, but at a low rate, until the timeat which the larvae reach a length of 40 mm. Beyondthe 40 mm length the number of larvae containing foodincreases clearly and in the juveniles of 50.0-90.0 mmthis number reaches a more or less constant and ratherhigh level. It should be emphasized that the fact thatlarvae which did not contain food were found in sucha scarce number has been experienced during 3 years.regardless of the season of the year.This low incidence of feeding found in larvae of aspecies of the family Engraulidae is not an isolatedfact, but has been observed with different species ofthis family and of those of the Clupeidae. Berner(1959) while studying the feeding habits of the northernanchovy, Engradis waordax found that amongthe 13,620 larvae which he examined only 211 had ingestedany food. Lebour (1921), who studied the foodhabits of numerous young clupeids, found that thepercentage of individuals containing food was verylow. The incidence of feeding in the larvae of othergroups of fishes appears to be higher (Lebour 1920,Wiborg 1948, etc). While studying the food of thelarvae and juveniles of A. incisa which were collectedtogether with those of the anchovy (Ciechomski, inpress) the present author found that all of the individualswhich were examined contained food in theirintestinal tract.The phenomenon of the low incidence of feeding inthe families Engraulidae and Clupeidae has been asubject of detailed analysis by numerous authors.There exist, as a consequence, several theories whichattempt to explain this fact. Some authors try to explainthis phenomenon as a consequence of the selectivityof the nets, which would tend to collect thoselarvae which were weak and underfed (Berner 1959,Soleim 1942, and others). Other authors think ofthis phenomenon as a consequence of the characteristicsof the digestion of these species, which, accordingto them, is very rapid. The old theory of Putter, accordingto whom fishes are able to feed upon theorganic matter which is dissolved in the water, hasbeen sustained by Morris (1955). This author thinksthis possible on the basis of the fact that the larvae