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water and up to 3.0 units in deionized water) duringadditions of the acid standard solution (Sekerka, Can-ada Centre for Inland Waters, Burlington; Wagemann.Freshwater Institute, Winnipeg; personal communica-tion). Thus absolute readings of ,'free" ionized copperby the electrode are questionable and the data cor-respond rather to "electrode detectable" copperanalogous to "labile" copper as described by Chau andLum-Shue-Chan (1974). Despite this the electrode isa useful tool in monitoring relative changes in con-centration of copper added to lakes or tanks over aperiod of time in algae and fish toxicity studies.

Acknowledgments - I am gratefully indebted to DrsF. A. J. Armstrong, R. Wagemann, I. Sekerka, and y. K,Chau for critical comments on the manuscr.ipt. and to J.Gibson, M. Buckley, and H. Majewski for their laboratoryand field assistance. Measurements of total copper byatomic absorption spectrophotometry were done by B. Huntand A. Lutz.

Received May 12, 1977Accepted October 12, 1977

'Present address: D6partement de biologie, Facult6 desSciences et de G6nie, Universit6 Laval, Cit6 Universitaire,Qu6bec, Qu6. GlK 7P4

Printed in Canada (J4828)Imprim6 au Canada (J4828 )

Cnru, Y. K., nxp K. Lurrt-SHue-Cstn.7974. Determinationof labile and strongly bound metals in lake water.Water Res. 8: 383-388.

EIFAC. 7976. Water quality criteria for European fresh,water fish: report on copper and freshwater fish.EIFAC (Eur. Inland Fish. Adv. Comm.) Tech. Rep.27 : 21 p .

Lroyo, R. 1965. Factors that afiect the tolerance of fish toheavy metal poisoning, p. 181-187. In C. D. Tarzwell[ed.] Biological problems in water pollution. U.S. Dep.Health, Education and Welfare. 424 p.

OntoN RssrencH INc. 1975. Instruction manual: cupric ionelectrode model 94-20. Cambridge, Mass. 28 p.

StuEN, L. G., exo A. E. Manrer-. 1964. Stability constantsof metal-ion complexes. Chem. Soc. London Spec. Publ.No. 17: 754 p.

Svr-vl, R. N. 1976. The environmental chemistry of copper(II) in aquatic systems. Water Res. l0: 789-792.

Wnrrexrn, J. M.. J. BARrcA, H. KrrNc. eNo M. Bucrrr,y.1978. Efficacy of copper sulfate in the suppression ofAphanizomenon flos-aquae blooms in prairie ponds.Environ. Pollut. (In press)

Regu le 12 mai 1977Accept6 le 12 octobre 1977

ArtHoucH the use of radioisotopes for marking fish isnow well established (e.g. Scott 1961,1962; Hoss 1967;Carlson and Shealy 197 2; Peters and Hoss 197 4), radio-active tags have seldom been used to document preda-tion. An exception is Carlson and Shealy (1972). whofound that radioactive tagging was suitable for studies

Technique for Tagging Smatl Fish with I'"'for Evaluation of Predator-Prey Relationships

Gnnnnn J. FtrzGpnet-Dl AND Mrtns H. A. KBsI.{rEysrDEDepartment ot' Zoology, (Jniversity of llestern Ontario, London, Ont.

FnzGnae'ro, G. J., aNo M. H. A. Kprnuvsror. 1978. Technique for tagging small fishwith 11"' for evaluation of predator-prey relationships. J. Fish. Res. Board Can.3 5 : 1 4 3 - 1 4 5 .

Experiments to test the feasibility of using radioactive I'"' as a technique for evalua-tion of conspecific predation on fry by adult convict cichlids (Cichlasoma n-igrolasciatum)are described. The technique is useful for short-term quantitative studies of predator-preyinteractions where it is not possible to observe and quantify predation direitly or wh"restomach content analysis of adults is not feasible.

Key words: radioactive tagging, predator-prey interactions, cichlasoma nigrofasciatum

FrrzGBnero, G. J., eNo M. H. A. KspNr-svsrns. 1978. Technique for tagging small fishwith I1*' for evaluation of predator-prey relationships. J. Fish. Res. Board Can.35: 143-145.

Nous d6crivons des exp6riences visant i vdrifier la faisabilit6 d'une technique utilisantl'isotope radioactif I'"'pour l'6valuation de la pr6dation des adultes aux d6pens des alevinsd.e Cichlasoma nigrofasciatum. Cette technique s'est av6r6e utile pour les 6tudes quantita-tives i coutt terme des interactions pr6dateur-proie, lorsqu'il est impossible d'observer etde quantifier directement la pr6dation ou d'analyser les contenus stomacaux des adultes.

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r44 J. FISH. RES. BOARD CAN.. VOL, 35. 1978

of invertebrate predators on prolarval largemouth bass.This note describes a technique for tagging young

free-swimming convict cichlids (Cichlasoma nigro-fasciatum) for evaluation of conspecific predation onfry by adults (FitzGerald 1976). We were interestedin identifying which particular flsh in a small pool atethe young fish. Neither visual observation of predationnor stomach content analysis was feasible in this study.

The technique involved labeling fry with radioactive1131 and later measuring the level of radioactivity inadult fish held in the same container. This isotope wasselected for several reasons. It is readily absorbed fromthe animal gut, most of it ending up in the thyroidgland. It has a short half-life (8.5 days) and a strongrate of gamma emission (Thornburn 1972). These fac-tors were important for safety reasons and because avery dilute system was used (food-fry-adults).

Preparation ol labeled lood - A commercially preparedradiopharmaceutical, I'"'-Triolein (glyceryl trioleate; Mal-linckrodt Chemical Works, St. Louis, Mo.) was used totag the food (egg yolk). It is one of the chief constituentsof oils and fats of animal and vegetable origin.

The procedure was to aggregate 1 mL of egg yolk withI mCi of tagged Triolein at 80'C with mortar and pestle.The supernatant was then centrifuged. Preparation andstorage of tagged food and all radioactivity measurementswere done in the Department of Nuclear Medicine, Uni-versity Hospital, University of Western Ontario. Feedingof fry, several pilot studies, and the use of the techniqueas part of a larger study (FitzGerald 1976) were done in aspecial Zoology Department radioactivity laboratory. Amultichannel sodium-iodide scintillation (Tobor) counterwas used to record radioactivity. Five replicate measuresof radioactivity (in counts per minute) were taken on allsamples of food, fry, adults, and holding water. All countswere corrected for background radiation levels and naturaldecay rate.

The tagging of fry and their introduction into pools con-taining adult fish presented several technical and logisticalproblems. A series of investigations was performed to de-termine (1) whether fry would eat the tagged food, (2) thelength of time that detectable amounts of radioactivityremained in the fry, (3) the behavior of tagged fry incomparison with untagged controls, (4) whether adult fishwould consume tagged fry, and (5) the length of timethat detectable amounts of radioactivity remained in theadults.

Tagging the fry -Fry were tagged as follows: ap-proximately 200 5-7-day-old fry were placed in a smallaquarium (40 X 26 x 22 cm) where they were givenexcess quantities of radioactive food and allowed tofeed for 24 h. There were no readily observable dif-ferences in feeding and locomotor behavior betweentagged fry and controls. They were then captured bydip net, rinsed twice in aged, uncontaminated waterand placed in a second small aquarium containing non-radioactive water. At 6-h intervals, beginning imme-diately after removal from the feeding tank and ending48 h later, 15 fry were removed by dip net, rinsed, anddried of excess water. Thev were then placed in a

aoo

200

o 1 2 2 4 3 6 4 8TITE AFTEB RETOYAL FROT FOOO(H)

Frc. 1. Change in radioactivity of C. nigrofasciatum frymeasured at 6-h intervals beginning immediately after re-moval from tank containing radioactive food. Solid circlesare means (-r 1so) of five measurements (counts per min-ute, CPM) taken on separate samples of 15 5-7-day-oldfry. No data available at 42h. Open circles show naturaldecay rate of the I'"' isotope.

sterile. uncontaminated plastic test tube and theirradioactivity levels measured.

Our data (Fig. 1) show that radioactivity in the frycould be measured for at least 48 h after removalfrom labeled food. If longer counting periods (e.g. 5rather than I min) had been used, the length of timethe tag could be detected would be increased.

Tagging the adults -Three adult C. nigrolasciatum(9.0-10.0 cm total length) were selected from a stockpopulation. Each was placed in a separate smallaquarium and given access to 15 tagged fry. Thesesamples of 15 fry had a mean count of 702 counts/minwhen given to adults. The number of fry consumed byeach adult within 24 h was recorded and the radio-activity level of each adult then determined.

The adult fish were removed from their aquaria andplaced in a jar of uncontaminated water. Each animalwas rinsed again in tap water, wrapped in wet papertowel, placed inside a small plastic bag, and finallyplaced in the Tobor scintillator counter. Upon returnto the laboratory they showed no apparent ill effectsfrom the handling and counting procedures. Meancounts per minute (-+l so) of f lve counts on each f lsh(Table 1 ) show that adult fish are detectably radio-active for at least 24h after consuming tagged fry.

The technique described here is useftll for short-term quantitative studies of predator-prey interactionswhere it is not possible to observe and quantify preda-t ion direct ly or where the ki l l ing of adult animals forstomach analysis is not possible. The technique mayalso be useful in tagging aquatic organisms for otherpurposes where an easily detected but short half-lifeisotope is needed.

O NATURALOECAY OF

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Subject no. Radioactivity No. fry consumed

t45

CenLsoN, C. A., aNo M. H. Snper-v. 1972. Marking larvallargemouth bass with radiostrontium. J. Fish. Res.Board Can. 29: 455-458.

FrrzGEnero, G. i. 1976. The effects of density of adultfish on reproduction and parental behavior in the con-vict cichlid fish Cichlasoma nigrolasciatzn (Giinther),Ph.D. Thesis. Univ. Western Ontario, London, Ont.203 p.

Hoss, D. E. 1967. Marking post-larval paralichthid flounderwith radioactive elements. Trans. Am. Fish. Soc. 96:I 5 1-l 56.

PETERs, D. S., exo D. E. Hoss. 1974. A radioactive methodof measuring food evacuation time. Trans. Am. Fish.Soc.103: 626-629.

Scor'r, D. P. 1961. Radioactive iron as a flsh mark. J. Fish.Res. Board Can. 18: 383-391.

1962. Radioactive caesiurn as a fish and lampreymark. J. Fish. Res. Board Can. 19: 149-157.

TnonNnunx, C. C. 1972. Isotopes and radiation in biology.John Wiley and Sons, Inc., New York, N.Y. 287 p.

Regu le 72 octobre 1976Accept6 le 1 septembre 1977

NOTES

TAsre 1. Radioactivity of adult C. nigrofasciatum after con-suming tagged fry. Data are means ( + I sD) of five measure-ments (ln counts per minute) corrected for backgroundradiation and natural decay of the isotope.

I 656 +892 696+613 617 +42

15l 5t 3

Acknowledgments -The technical expertise of Mr p.McKinnie was essential to the develoDment of the tech-nique. Dr M. L. Chamberlain suggestei rhe procedure fortagging fry and permitted us to use the facilities of theDepartment of Nuclear Medicine. The advice of Dr B. G.Atkinson is greatly appreciated. The work was supportedby a National Research Council Grant to M. Keenlevside.

variation in Age at First spawning in Atlantic salmon (sahno salar)

GuNNa.n N.c,voAL, Ma,RnNNp Holtr, Oscan INcnsnIcrsBN, AND Dec M@rrnn

Institute of Marine Research, Bergen, Norway

N,evoer, G., M. Hor-rr, O. IxcennrcrsEN, AND D. M@rrrn. 197g. Variation in age atfirst spawning in Atlantic salmon (Salmo salar). J. Fish. Res. Board Can. 35:145-147.

Significant differences in the proportion of mature fish in groups of Atlantic salmon(Salmo salar) of different river origins maintained under the same conditions were ob-served during the lst and 2ndyr of sea rearing. Nearly all fish in sib groups or.iginatingfrom grilse rivers matured during the 2nd sea year, while few or no mature fish werefound in the groups originating from rivers producing mainly multi-sea-winter salmon.The observations were in accordance with the life histories of the different river popula-tions, indicating that salmon inherit rather than acquire a tendency to mature at acertain age.

Key words: Atlantic salmon, maturation age, cultured salmon, river populations

N,evoer, G., M. Horu, O. INcEnnrcrsEN, AND D. M@nrn. 1978. Variation in age atfirst spawning in Atlantic salmon (Salmo salar). !. Fish. Res. Board Can. 35:145-147.

Nous avons observ6 durant la lre et la 2e ad'lleva$e en mer des diff6rences significa-tives dans la proportion de poissons m0rs dans des groupes de saumons atlantique (Satmosalar) provenant de diff6rentes rividres et maintenus dans des conditions identiques.Presque tous les poissons de prog6nitures provenant de rividres i grilse atteignent lamaturit6 au cours de leur 2e a en mer, alors qu'on trouve peu ou pas de poissons mtrsdans les groupes provenant de rividres qui produisent en grande partie des saumons deplusieurs hivers en mer. ces observations sont conformes au cycle biologique des popula-tions des diff6rentes rividres, ce qui indique que Ia tendance i atteindre Ia maturii6 i uncertain dge est h6r6ditaire et non acquise chez le saumon.

Received October 12, 1976Accepted September l, 1977

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