+ University of Bergen

Transcription

1 This paper not to be cited without prior reference to the authors. Internationa Counci for the Exporation of the Sea CM 1981/H:31 Peagic Fish Committee "GROWTH PATTERNS IN OTOLITHS AS AN INDICATION OF DAILY GROWTH VARIATIONS OF LARVAL HERRING (CLUPEA HARENGUS) FROM AN EXPERI MENTAL ECOSYSTEM" by + ++ Harad Gøsæter and Victor Øiestad + University of Bergen Department of Fisheries Bioogy N-5011 Bergen/Nordnes, Norway. ++ Institute of Marine Research N-5011 Bergen/Nordnes, Norway. ABSTRACT Larva herring were reeased in a afge outdoor basin four days after hatching and the mean growth in ength and weight of the herring arvae and fry was monitored for 100 days. The food suppy was estimated from weeky samping of zoopankton. At termination of the experiment herring fry were coected and the width of the daiy growth zones were measured in the otoiths of sorne of the herring fry. The mean zone width on a day to day basis mimiced the mean arva growth rate. As the variation in food suppy determined the growth rate, there was aso a cose reation between mean zone width and the food suppy. A method for measuring the.zone widths by means of a digitazing board is describede

2 -2- INTRODUCTION Primary growth zones, which are found in the otoiths of a variety of fish species, are in many cases shown to be formed daiy. If there exists a reationship between growth of the fish and its otoiths, then the width of these daiy growth zones shoud refect the growth of the fish on a day to day basis. Anaysing the growth pattern of the otoiths woud then be a usefu method of studying the growth characteristics of individua fish and popuations. Some workers have used the method of reading daiy growth zones in ageing some arva! fish, e.g. Barkman. (1978), Brothers, Mathews and Lasker (1976), Lou.gh et a. (1980), Methot (1979), Radtke (1980), Radtke and Waiwood (1980) and Taubert and Cobe (1977) ø In this paper the daiy. growth zone method has bee ri appied to describe the growth of herring arvae from an encosure experiment, where food suppy and growth rate of the herring was known, and has earier been des:cr1bed by' Øies:ta'd and Moksnes s (1979). MATERIALS AND METHODS Eggs of Norwegian spring spawning herring were incubated in the aboratory at Statens Bioogiske Stason FØdevigen at 5 March Hatching occured at 4 Apri. The arvae were reeased in a arge outdoor basin four days ater. The experimerit was terminated at Juy 12-13, wheri the arvae were days od, cacuated from the day of 50% htchig. Sampes of the zoopankton in the basin were taken at weeky intervas and sampes of herring arv.ae two times per week to start of schooing and ater wee'ky. The growth of the herring arvae and fry has beeri indicated both as specific growth rate (SGR) based on arva! dry weight and as daiy ength increment (DLI). The feeding conditions are expressed both as number of organisms

3 -3- per itre and as ca per itre. At termination of the experiment a sampe of herring arvae was frozen and brought to the Institute of Fishery Bioogy at the University of Bergen for examination of the otoiths. From this sampe a subsampe containing 20 arvae was ater on taken and treated as foows: The standard ength was mesured to the nearest mm beow and the two sagittae were removedo They were positioned on gass sides, one with convex, the other with concave side up, in a drop of syntetic mounting medium Protexx. They were eft to dry for about 24 hours, and then inspected in a compound microscope. In the smaest otoiths aying concave side up, the primary growth zones were discernabe without further treatment. The others were grinded using 800 grit siicon carbide paper immersed in water in a arge petri dish. The otoiths were frequenty inspected in the microscope, and the grinding prosess was terminated as the zones became visibe from center to edge. The otoiths were then photographed on a 400 ASA back & white fim, using photographic equiprnent attached to the microscope. The magnification used was 100 to 250 X. After deveoping the fim, the negatives were mounted in side frames and proected on a digitizing board with a side proector instaed in a vertica position above the tabeø To ensure that the zone width shoud be comparabe, an.identica radius was photographed for a otoiths, viz. the radius to the dorsa edge perpendicuar to the radius through rostrum. A white sheet of paper was positioned on the digitizing board, a straight ine representing the radius aong which the measurernent was to be done. The zones aong this radius were then digitized by means of a cursor moved aong the ine pushing a button for each zone, thus making the coordinates of each point to be stored in a computer. The measurement of the board was scaed to rea size by comparing the ength of the whoe radius measured on the board wi th measurements of.the same radius in the microscope. The width of the zones were then computed and the.data obtained as zone number and zone width in micrometer..

4 -4- RESULTS Food suppy and growth respons. The amount of food organisms expressed as number per itre, increased to day 50 when a sudden coaps in the popuation of hoopeagic zoopankton popuations took pace, Fig.. The number of ca per itre continued, however, to increase beyond day 50 due to an incusion of semipeagic food organisms in the diet, mainy uveni amphipods, but these semipeagic organisms were far ess avaiabe than the hoopeagic organisms as food for the herring fry. The specific growth rate increased with increasing food suppy and decreased at the time of coaps in the hoopeagic zoopankton popuations, Fig.2o The daiy ength increment increased aso with increasing food suppy, but did not decrease at the time of coaps in the hoopeagic zoopankton. However, when aso the semipeagic zoopankton was heaviy reduced from day 70 the DLI decreased sharpy. Zone width. Athough the zones coud be counted in one or both otoiths from the maority of arvae, ony otoiths from ten specimens were used in the measuring of zone widths. Ony those otoiths considered to have the highest quaity were used. The reason for this truncation of data was that in some otoith pictures it was impossibe to see a the zones aong the particuar choosen radius. This was partiay caused by some otoiths aying with their grinded surface (or the pane where the zones best coud be seen) at an ange to the microscope side. As the focusing depth of the microscope is imited, it was sometimes impossibe to get a sharp image of the entire radius on one photo. The width of each zone averaged over the ten specimens is potted against age in Fig.3. The standard deviation is given for every 5. day. It has been shown earier (Gøsæter, 1981) that the first zone for this group was aid down in the otoths when the arvae were about 4-5 days od or at first feeding opportunity. The first zone is in this study assumed t five days correspond to a arva! age of This gives a mean a of the ten arvae of 97 days,

5 -5- which is fairy cose to the rea age of 99 days for the sampe. This mean age has a standard deviation of 3.4 days. The mean zone width increases from about 3 m near the nuceus to a peak of 7-8 mon day (Fig.3). Then the zone width decreases during the next 15 days to 4 m, whereafter there is a further sight decrease to 3 m unti termination of the experiment DISCUSSION Two assumptions underie -. the interpretation of the zone width as a measure of fish growth. The first is that the zones are deposited on the otoith with a reguar periodicity. If the zone width is used in backcacuation of fish growth, this periodicity must be knownø Secondy, a functiona reationship between fish size and otoith size must exist and be known. Using herring arvae from this and other basin experiments in FØdevigen it has been shown that the primary growth zones are aid down with a daiy periodicity for at east 135 days (Gøsæter, 1981). As to the second assumption the data are somewhat sparce, but they indicate a inear reationship between the measured otoith radius and the fish ength. This irnpies that there is a direct proportionaity between growth zone width and fish growth in ength of herring arvae up to about 50 mm SL.. The reduction in width started at about the same time as the reduction in SGR, and the width made a new decine when aso the DLI went down.. A comparison of the variations of zoopankton (Fig.) and mean zone width (Fig.3) with age reveas a high.degree of covariation. Thus we have obtained two independent measures of the mean growth rate of the herring arvae and fry: the SGR and DLI as cacuated from frequent samping of the popuation, which is a direct method of rneasuring growth, and the otoith zone width, as measured in the otoiths from the arvae aive at termination of the experiment.

6 -6- The ast method being indirect is seemingy abe to detect the variations in mean growth rate with time. This variation is determined by the amount of avaiabe food. This method can aso be used to demonstrate individua growth varitions, and from an ecoogica point of view the individua growth of a arva is of great interest. CONCLUSION If a functiona reationship between a measure of otoith size and fish size can beestabished, the measuring of daiy growth zone width can be used to backcacuate the growth of individua arvae from first feeding to the time of samping, and shoud therefore be of great appicabiity in studies om arva bioogy and ecoogy.. REFERENCES Barkman, R.C., 1978: The use of Otoith Growth Rings to Age Young Atantic Siversides, Men:fdia me:nidia. Trans. Am. Fish. Soc. 107(6): Brothers, E.B., Mathews, C.P. and Lasker, R., 1976: Daiy growth increments in otoiths from arva and adut fishes. Fish.Bu. 74 () :1-8. GØsæter, H., 1981: Dagsoneesi:ng som metode i adersstudier på fisk, med eksemper på anvendese på tropiske og boreae arter. Thesis, 172 pp. University of Bergen, Norway. Lough, P.G., Pennington, M.R., Boz, G.R. and Rosenberg, A.A., 1980: A growth mode for arva sea herring Cupea harengus in the Georges Bank - Guf of Maine area based on otoith growth increments. Int. Coun. Expor. Sea CM 1980/H: 65. [Mirneo]. Methot, R.D.re, 1979: Spatia covariation of daiy growth rates of arva northern anchovy Engrauis mordax and northern ampfish Stenobrachius eucopsaurus. Presented at ICES/ELH Symposium Woods Hoe USA SD: 11, 25 pp.. LMimeo]. '

7 -7- Radtke, R.L, 1980: The Formation and Growth of Otoiths from Redfish Sebastes spp ). Larvae from the Fernish Cap (Division SoM.) NAFO SCR Doc. 80/ Ser No N PP Rad"tke, Ro L ø and 1!\Taiwood, K G.., 1980: Otoi th Format ion and Body Schrinkage due to Fixation in Larva Cod '(Gadus orhua). Can. Techo.:. Fisho Ag.. Sei.. No pp. Taubert, B.. D. Cobe, DoW., 1977: Daiy Rings in Otoiths of Three Species of Lepomis and Tiapia mosambica. J. Fish. Resø Board Can. 34: Øiestad, V and Moksness, E., Interaction between Atanto Scandian herring arvae (Cupea harengus) and capein arvae (Maotus viosus in a concrete encosure experimento Intø Coune Expor. Sea. CM 1979/F:52. [Mirneo].

8 ::s:! a_ --- (...) - C?.i CAL PR. LI TRE ::s:! 1-- NUME3ER PR. LI TRE --- a_ 0-.J... -" ' ' ' ' 0-.J ' ' ' ' \ \ \ \ ' ' \ ' ' \ \ \ V ' ' ' ' ' ' ' AGE IN CAYS f-- LW (_) LW a_ LJ..J f-- - f-- :::.;, (_!:) u._ (_) LJ..J CL (_f)... SPEC F C GROWTH RATE ::c "' LJ..J ':!2 ::i -..r: c::::: - 9 ::c f-- LJ..J ::c (_) 1-- as LLJ J o 2a 40 sa sa 1ao 0 AGE IN DAYS , a aO AGE IN CAYS Figs., 2 and 3. Nurnber of potensia food organisrns per itre for herring arvae and fry, and ca per itre of suitabe food organisms (); specific growth rate and daiy ength increment of the herring arvae and fry (2); and zone width of the daiy growth zone in the otoiths with standard deviation for every five day indicated (vertica bars) (3).

9 Fig.4 A section of a otoith from a 100 days od herring fry, which iustrates diferent width of the growth zones.

10 J