OXYTETRACYCLINE MARKING STUDIES OF TILAPIA; OREOCHROMIS ...s/OTC marking of... · OXYTETRACYCLINE MARKING STUDIES OF TILAPIA; OREOCHROMIS NILOTICUS Y. M. Abdel-Hadi 1, 2, J. F. Craig

OXYTETRACYCLINE MARKING STUDIES OF TILAPIA;

OREOCHROMIS NILOTICUS

Y. M. Abdel-Hadi 1, 2, J. F. Craig 3, J. A. Babaluk 4 and R. Wassle

1 Aquaculture Dept., Faculty of Agriculture, University of Putra Malaysia (UPM), Serdang, Selangor, Malaysia.

2 Central Laboratory for Aquaculture Research (CLAR), Abbassa, Egypt.

3 Whiteside, Dunscore, Dumfries, DG2 0UU, Scotland, U.K.

4 Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba, Canada

I- IntroductionSince oxytetracycline is incorporated into

newly forming calcified tissue and is visibleunder ultraviolet light as a fluorescent band,it had been used periodically by fisheriesresearchers as a marking tool.

Since that time, tetracycline has been usedwidely as a means of marking.

Applied at a known date, tetracycline has beenused to validate methods of fish agedetermination.

Importance of fish aging

Fish age determination has been used in fisheries management:

• Stock assessment.

• Age of capture and marketing.

• Age of sexual maturity.

• Different Biological studies.

von Bertalanffy growth equation

• The individual growth model published by Karl Ludwigvon Bertalanffy in 1934 is widely used in biologicalmodels and exists in a number of permutations.

• In its simplest version the so-called von Bertalanffygrowth equation is expressed as a differentialequation of length (L) over time (t):

L/(t) = rB (L∞ - L (t))

• when rB is the von Bertalanffy growth rate, L∞

is the ultimate length of the individual and t is the

time or age.

II- ObjectivesIn this study, tetracycline was injected into tilapia,

Oreochromis niloticus to validate 4 agedetermination methods (scales, opercula,otoliths' and pelvic fin rays' sections):

• Tilapia fish aging reliability in Egypt.

• To assess tetracycline-induced mortality.

• To determine how quickly it was incorporatedinto calcifying tissues of Tilapia.

• To determine the suitable marking dosage oftetracycline for this freshwater species.

Materials and methodsFish:

• A number of 1200 fingerlings of monosexOreochromis niloticus were used for the study.The fish were acclimatized first and distributedinto 4 raceways (300 per each raceway).

• The average body weight at the time of injectionof the OTC on September 1st, 1998 was 60 gramand the average total length was 15 cm.

Raceways:

• Four raceways were used for rearing the fish foran entire year, which was the period of theexperiment.

• The dimensions of each raceway were 50 meterslong, 4 meters width and 1 meter of water depth.

• The experiment was carried out in the facilities ofthe WorldFish Centre (The Regional Centre forAfrica & west Asia at Abbassa,, Egypt) for 1 year.

Selection of Oxytetracycline dosages

• The fish in the 1st group were injected with OTC ina dose of 12.5 mg/kg fish body weight and thenreleased into the first raceway.

• The fish in the 2nd group were injected with OTC ina dose of 25 mg/kg fish body weight and thenreleased into the second raceway.

• While, the fish in the 3rd group were injected withOTC in a dose of 50 mg/kg fish body weight andthen released into the third raceway.

• On the other hand, the fish of the 4th

group were injected with sterile distilledwater and then released to the 4th racewayto be kept as a control group.

• The fish were injected intraperitoneally(I/P) using an automatic syringe similar tothat used in mass injection of chickens inpoultry farms.

Automatice Syringe

Sampling regime

• One fish from the fish kept in the controlhapa and 5 from the fish injected with 50mg/kg.b.wt. were taken periodically after 6,12, 24, 48, 72 and 96 hours. Then after 1, 2and 4 weeks respectively.

• Periodical sampling of 5 fish from the 4treatments in a monthly basis was carriedusing trammel net.

• Those 5 fish from each

treatment were sacrificed.

• Each fish was numbered, weighed and thetotal body length was measured.

• The fish were then dissected. Differentbony structures were taken from eachfish, which are scales, opercula, otoliths

and pelvic fins.

Examination of different bony structures

• Opercula:

were examined whole on a black background with a stereoscopic microscope with a hand-held reflective ultraviolet light source. The viewing room was dark.

• Scales, otolith sections, and fin ray sectionswere examined under reflected ultraviolet light using a fluorescence microscope.

Results

Age validation:

• There was quite a bit of growth on all structuresafter the OTC mark. It also appears that the fishwere at large long enough so that an “annulus” or“check” had been formed after the OTC mark.

• This was especially evident on the pelvic fin rays andopercula.

• Thus, all examined bony structures were found to bereliable and valid for aging of Oreochromis niloticus in

Egypt.

• Time of annulus formation was on May depending on scales' back calculations (Figure. 1).

• On the other hand, its time may be on April according to opercula's back-calculations (Figure. 2).

Figure. 1 Back-calculations using scales radii

N.B. Notice the stunted growth during winter months (In January, February & March).

R =

Average total scale radius in mm (sampled from 5 fish).

0

50

100

150

200

250

300

350

Len

gth

in

mm

Date from September 1998 to September 1999

Fig. 1 The relationship between age, total body length (T.L.) & scale radius (R)

Date

Average T.L. mm

R mm

Figure. 2 Back-calculations using opercula radii

R = Average total operculum radius in mm.

0

50

100

150

200

250

300

Len

gth

in

mm

Date from September 1998 to September 1999

Fig.2 The relationship between age of fish, total body length and operculum radius

Date in month

Total body length in mm

total operculum radius (R in mm)

Oxytetracycline-induced mortality

Treatment Total mortality

12.5 mg/kg fish 2.7%

25 mg/kg 0.3%

50 mg/kg 1.3%

Control group 2.7 %

Oxytetracycline uptake & dosage

All the 3 dosages were sufficient to mark the various bony structures. OTC marks were clearly evident on all structures from OTC-injected fish that were at large for one month.

The 25 and 50 mg/kg gave strong OTC marks

In all of these cases, there was visible growth onthe bony structure after the OTC mark.

Figure. 3 Transverse section of an otolith from a tilapia injected with 25 mg oxytetracycline/kg body weight (a) reflected ultraviolet light and

b) transmitted white light. Annuli are indicated by dots.

• Oxytetracycline mark (OTC) is also indicated. Bar = 0.5 mm.

Figure. 4 Transverse section of a pelvic fin ray from a tilapia 9 months after oxytetracycline injection

Figure. 5 Transverse section of an otolith from a tilapia 9 months after oxytetracycline injection

Figure. 6 Transverse section of an otolith from a tilapia 2 months after oxytetracycline injection

Figure. 7 Transverse section of an otolith from a tilapia 48 hours after oxytetracycline injection

Conclusion

• It could be concluded that tilapia fish

aging is reliable in Egypt as a subtropicalcountry and can be used as a basis forstock assessment and other fisheriesmanagement applications.

• The dose of 25 mg OTC/kg body weight

for marking of tilapia is recommended in

subsequent work & future studies.

Acknowledgment

• The authors are very grateful to the WorldFish Centre andits entire staff (Regional Center for Africa and West Asia,Abbassa, Egypt), where the experiment was carried out.Special thanks to Dr. Roger Row (the former deputydirector general), Engineer Rezk Hara and his team.

• The authors also appreciate the kind support of Dr. IsmailRadwan who granted the fish of the experiment as a giftfrom his own hatchery in Kafr El-Sheikh, Egypt.

• Sincere thanks are directed to UPM for sponsoring mytravel and participation in this big event.