FISHEBIES RESEARCH BOABD.,OF ' CANADA -

Transcription

1 ' f (6)~ ad(',», " 9,., ' This series includes utlp lilil~5)q~d prej.iminwy,reports,' and data re~ords 'not - i.nte ilf91f8ut~ r~ooidr~~ipdaij~.a. They should not be referred to In puliil1cahon-s, wmi- - outdearance inj'in f.he~ iss&m!~~e~~ lishment and - withou:t e;jear indica;t'ior,0tmli_'$j1~,,; FISHEBIES RESEARCH BOABD.,OF ' CANADA - MANUSCRIPT REPORT SERIES NQ ," -. Relationship ' hetwe:en V e'fteb~a ' Diameter and Fish Length 'and Usefulness of Marking Vertebra of Youn,g ~Coh\o Salmon.(Oncorhynchus ki;s~utchl " with Oxytetracyclin,e by _ H. T. Bilton, D. W. Jenkinson, and R. M. HUinph~;ey's Pacific Biological Station, Nanaimo, n.c. May 1974

2 This series includes unpublished preliminary reports and data records not intended for general distribution. They should not be referred to in publications without clearance from the issuing Board establishment and without clear indication of their manuscript status. FISHERIES RESEARCH BOARD OF CANADA MANUSCRIPT REPORT SERIES No Relationship between Vertebra Diameter and Fish Length and Usefulness of Marking Vertebra of Young Coho Salmon (Oncorhynchus kisutch) with Oxytetracycline by H. T. Bilton, D. W. Jenkinson and R. M. Humphreys Pacific Biological Station, Nanaimo, B.C. May 1974

3 INTRODUCTION Tetracyclines have been found useful in marking bones of Pacific salmon (Weber and Ridgeway 1962; Jones and Steel 1965; Jones and Swartz 1966; Jones 1969). When antibiotics of the tetracycline series are fed to growing animals, residue of the drug is fixed in bone tissue and this will fluoresce yellow under ultraviolet light. Oxytetracycline (OTC) levels in salmon have been investigated by Jones and Steel (1965) and Jones and Swartz (1966). Data were collected concerning efficiency of treatment, safety to the fish, tissue residue levels and content measures to ensure its accurate labelling and safe use (Jones 1969). It appears safe to use up to a maximum dosage of 1.0 g OTC per kilogram of fish weight over a 4-day period, followed by a 7-day holding period after feeding of the diet. Recent studies (Jones 1969) indicated that a suitable mark is produced with dosages of about 0.5 g per kilogram of fish over 4 to 13 days. The diet must not be fed to fish weighing more than 30 g (Jones 1969). The purpose of the present study was to determine if the length of young coho at time of marking could be estimated at a future date from examination of the mark that had been laid down on their vertebrae. MATERIALS AND METHODS (a) Donor stock One-year-old juvenile coho salmon of Big Qualicum River origin and reared at Rosewall Creek were used in the experiment. (b) Selection of experimental groups Fish were anesthetized with 2-phenoxyethanol, measured for fork length in millimeters and then placed into 5-mm length categories. Fish in each 5-mm length category were returned to a specific tank. The number of fish in each of the length categories ranged from two for the largest size to four in the smallest size group (Table 1). (c) Experimental apparatus Fish in each length category were held in separate 10 gal fiberglass circular tanks. Flow of river water to each tank was held at the same velocity of approximately 1 gal per minute. (d) Feeding Fish in the experimental groups were fed a mixture of 3% TM50D (a mixture of 5 g of tetramycine per pound in a sucrose kaoline base) at a rate of 5% of the body weight per day for a period of 14 days from June 11 to 24, From June 25 to September 5, 1973, fish were offered ad libitum Oregon moist pellet commercial food. Frequency of feeding followed normal hatchery procedures..

4 - 2 - (e) Sampling and measurement of vertebrae On September 5 all fish in the experimental groups were killed, measured for fork length, and frozen. At the laboratory in Nanaimo fish were thawed and the second vertebra from the head of each fish was dissected out for examination. Each vertebra was examined with a binocular microscope at a magnification of 25 times. The total diameter across the end of each vertebra was measured with an opti~ micrometer located in the eyepiece of the microscope. At the same time the diameter of the tetracycline mark was measured under ultraviolet illumination using a Hyland ultraviolet lamp (provides a 115 volt, 60 cycle, 0.12 amp source emitting ultraviolet light at 3,660 A which is completely safe for eyes and skin). RESULTS AND DISCUSSION From the total vertebra diameters (measured from fish sampled on September 5), the body length-v.=rtebra diameter relationship was determined (Table 2, Fig. 1). A highly significant correlation coefficient r of 0.850, n = 78, p <0.001 was indicated between vertebra diameter and body length. The regression formula was: (a) Fish length (rom Y = X (total vertebra diameter, rom). Using the diameter of tetracycline mark and the midpoint of the range of each length category on June 7, the body length-tetracycline mark relationship was determined (Table 2, Fig. 1). A highly significant correlation coefficient r of 0.890, n = 78, p <0.001 was indicated between vertebra diameter and body length. The regression formula was: (b) Fish length (mm) Y = X (diameter tetracycline mark, rom). Assessment of the precision that the length of the fish on June 7 could be estimated from the tetracycline mark was made using the regression formula for body length-total vertebra diameter (formula (a) above) (Table 3). In 7 of the 10 comparisons the mean estimated lengths were higher than the midpoint of the length categories on June 7 and in three comparisons they were lower. However, the differences were small, ranging from 0.6 (group G) to 4.0 rom (group H). In all but two cases (groups C, H) were the differences 3 rom and less. It thus appears possible to estimate with fair precision the lengths that returning coho adults had been, when they were released as smolts 1 or 2 years earlier from the diameter of the tetracycline mark that had been laid down prior to their release. Comparison of the mean length of fish in each group on September 5 with the midpoint of the length class to which they belonged on June 7 indicated a highly significant positive correlation (r = 0.937, n = 2, P <0.001). Thus it would appear that fish which were larger on June 7 continued to maintain this advantage over the smaller fish up to at least September 5.

5 - 3 - ACKNOWLEDGMENTS The authors would like to thank Dr. F. Neave for his critical review of the manuscript and Mr. G. E. Johnston for technical assistance in the rearing of the fish.. REFERENCES. Jones, I. W Notes on marking salmon fingerlings with tetracyclines. Fish. Comm. Oregon, Fish Culture Division, Clackamas, Oregon. 5 p. Jones, I. W., and R. Steel Tetracycline salmon marking studies. Fish. Comm. Oregon, Annu. Progr. Rep., Contract : 17 p. Jones, I. W., and D. F. Swartz Tetracycline salmon marking studies. Fish. Comm. Oregon Progr. Rep., Contract : 23 p. Weber, D. D., and G. J. Ridgeway The depositiou of tetracycline drugs in bones and scales of fish and its possible use for marking. Progr. Fish.-Cu1t. 24:

6 - 4 - Table 1. The number of young coho of each length category assigned to each of the experimental groups on June 7, Length category (nun) Group Range Midpoint No. fish F A B c D E G J K H

7 -.5 - Table 2. The means and ranges of body length and,totalvertebra diameter of each in each groqp of fish sampled on September 5, Length (nun) Total vertebra diameter(i:md) Group Range x Range x No. fish F A B C D E G J K H

8 ~ 6 - Table 3. The rtumberof young coho of each length category assigned to each of the experimental groups on June 7 and the estimated length of fish in each group on June 7 from tetracycline marks when sampled on September 5, Length category Estimated length (rrrrn) (rrrrn) on June 7 Group Range Midpoint No. fish Range Midpoint No. fish F A B C D E G J K H

9 .. ~ K E J 2 5 E E a: III t;j 2 0 Z «0 «II: III III I- a: III > 011 '" "" Z a: 1,5, DIAIotETER OF NARK (7JUNE 1973) Y 0 1I Il49X(FORK LENGTH) r: C a AC A C B B ko A -G EAC G DK J DIAMETER OF VERTEBRA E J H J K K G (5 SEPT 1973) Y X(FORK LENGTH) r ,J a " A FORK LENGTH (mm) Fig. 1. Shows relationships between tetracycline mark diameter and fish length on June 7 (lower case letters) and total vertebra diameter and fish length on September 5, 1973 (upper case letters). 210