I ACTA HYDROBIOL .. j I 334

Growth of Tilapia zilli exposed to sublethal concentrationsof crude extracts of Azadirachta indica

Edosa Omoregie, Martin A. Okpanachi

University of Jos, Department of Zoology,Fisheries Research Unit,P.M.B.2084, Jos, Nigeria

Manuscript submitted January 9, 1992, accepted September 22, 1992

A b s t r act - The effects on growth of Tilapia zilli exposed for 12 weeksto sublethal crude extracts of Azadirachta indica was investigated in staticbioassays and a constant aeration system. Weight increased with the declineof nominal concentrations of the extracts. Long-term exposure of T. zilli tosublethal concentration of the extract caused growth retardation. The exposedfish showed abnormal behavioural responses at 1.56 and 0.78 mg dm", theseresponses being minimal at lower concentrations. The use by local fishermenof extracts of A. indica to kill fish is therefore ill-advised.

Key W 0 r d s: Tilapia zilli, Azadirachta indica, extract, growth,sublethal toxicity.

1. Introduction)

Man has always regarded plants as among the most valuedcomponents of our biosphere because of their uses as food andmedicine, and their chemical values. Nevertheless, some plants,such as Parkia clappertoniana, Azadirachta indica} Tephrosiaoogelii, Mundulea sericea, Boerhaauia coccinea, etc. have beenreported by R e e d et a1. (1969), G 1 ark e E. C. and M. L.C 1 ark e (1975), and Ad e - S err a n 0 (1982) to be poisonous toanimals, including fish. R e e d et al. (1969) reportedunconventional methods in the use of such plants by local fishermenin Nigeria. The crude extracts of leaves, bark, roots, fruits, andseeds are broadcast over the water surface, thereby resulting in thepoisoning of the fish which are then gathered from the water.

282

Ad e - S err an 0 (1982) observed that the leaves, fruits, seeds,roods, and bark of A. indica contain triterperenoid, azatin, solarim,and other active components with properties that are repellent andgrowth disruptive to living organisms. So f 0 w 0 r a (1978) notedthat A. indica products are known to have insecticidal activities.E k a n em (1978) reported a fall in the parasite count inchloroquinesensitive strains of Plasmodium berghei infected micewhen treated with A. indica leaf extract. 0 k pan y i andE z e u k w u (1981) have also documented that an extract from theleaves and bark showed an antipyretic effect, thus providing somejustification for its use in fevers.

The introduction such toxicants into the aquatic environmentcauses several disruptions in the aquatic productivity that w,iJJ.eventually lead to physiological disfunction in the aqua.organisms. One such effect is the reduction in growth of the aquaticfauna (War r e n 1977). A reduction in the growth of fish exposedto sublethal concentrations of toxicants was reported by B u 1 t e r(1974), Chi nab u t et al. (1987), and Ufo d i k e andOrne r g i e (1990). The distribution of Tilapia zilli is veryextensive in tropical freshwaters (R e e d, H 0 1 den 1972), henceits choice for the present study.

Its aim was to evaluate the effects of sublethal concentrations ofbark extracts of Azadirachta indica unconventionally used by localfishermen in rivers, streams, and lakes, on the growth of TiZapiazilli.

2. Material and methods

Fingerlings of T. zilli (mean weight, 5.01 ± 0.19 g) of the samebrood stock collected from Rockwater Fish Farm, Jos, were used fOT-the investigation. They were stocked at 10 fish per aquarium in iglass aquaria of 20 drrr' capacity. Each aquarium was supplied withdechlorinated, well aerated municipal tap water. Pelleted feed wasgiven twice daily at 4% body weight of the fish. They wereacclimated to laboratory conditions for 10 days prior to the exposureperiod. Mortality during the acclimation period was less than 3%.

The bark of A. indica was removed and dried in an oven at atemperature of 60°C for 5 days. The well-dried bark was pounded inclean mortar, sieved, and introduced to 6 glass aquaria at thefollowing concentrations, 1.56, 0.78, 0.39, 0.19, 0.09, and 0.00(control) mg dm", The remaining 6 aquaria served as replicates forthe first 6. The exposure period lasted 12 weeks during which each

283

aquarium was well aerated. Fresh preparations of concentrationswere introduced each week. While anaesthetized with benzocaine,the fish were individually weighted at the start of experiment andfortnightly thereafter. Mean weights were computed per treatmentfor each weighing period. The amounts of feed given were adjustedto the new weights. Some water quality parameters were monitoredeach 'morning according to the methods of APHA et al. (1980).Results· were subjected to statistical analysis with Duncan'smultiple-range F-test CDu n can 1955) to test for the level ofsignificance CP< 0.05) within the various concentrations.

Results

The water quality parameters in the various treatment did notvary significantly (P > 0.05) from those of the control (fig. 1).

24·60

romporalur. 24.50(oC) 24.40

24·30

6 ·80Dissolvtd axyoon 6.60

(mg dm-l)

6·40

2.40Carbon dioxide

(mg dm-3) 2·302.20

)36.80

Alkalinity 36.40(mg dm-3)

36.00

7·60

pH 7.40

7·20

Concentrations (mg dm-3)

• 1.56 mg dm-3

~ O.76mg dm-3[I]] O·39mg dm-3E3 0 .19mg dm-3

~ O.09mg dm-3o O·OOmg dm-3

Fig. 1. Mean water quality parameters during sublethal bioassays with Tilapia zilli

exposed to crude extracts of Azadirachta indica

284

However, the crude extracts led to a significant retardation in thegrowth of the fish (fig. 2). Statistical analysis showed that the fishexposed to the various sublethal concentrations had a significantlysmaller weight gain than the control fish (P < 0.05), the reductionbeing directly proportional to the increase in concentration. Thefollowing behavioural responses were observed in the fish exposed toconcentrations 1.56 and 0.78 mg dm='; undulations of the body,periodic bursts of erratic swimming, rapid opercular movements,surfacing and gulping air, increased oscillation of pectoral, pelvic,and caudal fins, increased secretion of mucus and defecation. Theseresponses were minimal in the fish exposed to lower concentrationsand were not observed in the control fish. Fish exposed to the crudeextracts had a curbed appetite, though with slow feeding all the fisteventually consumed the feed supplied.

14

12

102cd 801

~.~ 6QI~Co 4QI

~

2

0(,Extract concentrations (mg dm-J)

Fig. 2. Mean weight gain with standard deviation of Tilapia zilli exposed tosublethal crude extracts of Azadirachta indica

4. Discussion

A similar reduction in growth was observed by 0 lad i m e j iand 0 log u n met a (1987) when Oreochromis niloticus wereexposed to sublethal concentrations of lead, by Chi nab u t et al.(1987) when Cyprinus carpio were exposed to 4.5, 1.5, and 0.25 mgdrrr' of the insecticide Dipterex, and by Ufo d i k e andOm 0 reg i e (1990) when Tilapia nilotica were exposed to 1.00,0.50, 0.25, and 0.125 mg dm-3 of the insectides Gammalin 20

285

and Actellic 25 EC. The dose-dependent reduction reported in thepresent investigations was also noted by those workers. Earlierworks on the physiology of fish showed evidence of stress when theywere exposed to toxicants (G r i z z 1e 1977, DeS i 1v a,Ran a sin g he 1989, 0 m 0 reg i e et al. 1990). The inhibitionof growth reported in the present study may therefore be due to adisturbance of the normal metabolism by the crude extracts ofA. indica in the fish. So f 0 w 0 r a (1978) reported components in

: J the extract of this plant that have some growth disruptiveproperties to living organisms. Behavioural changes observed in theexposed fish were similar to those found in Cyprinus carpio(R a m e s h et al. 1986) and Tilapia mossambica

'.) (B ash a m 0 hid e e n, Red d y 1987). Some quantitativeaspects of behavioural changes with toxicants have also beenrecorded (P a 1, K 0 n a r 1987, G hat a k et al. 1987).

The use of crude extracts of A. indica and other similar plantsby local fishermen in rivers, streams, and lakes is very ill-advised,since the resultant deleterious effect on fish subjected to nominalchronic exposure is retardation in growth. The environmentalauthorities need to set quality criteria on the use of unconventionalfishing methods in the aquatic environment.

Acknowledgements - The authors wish to thank the Department ofZoologyof Jos, Nigeria, for supporting this research.

5. Polish summary

Wzrost ryby Tilapia zilli przetrzymywanej w subletalnychstezeniach surowego ekstraktu z Azadirachta indica

)Tilapia zilli byla przetrzyrnywana przez 12 tygodni w subletalnyeh stezeniach

surowego ekstraktu z kory rosliny Azadirachta indica. Przyrost ciezaru ryb bylsprawdzany co 2 tygodnie. Kontrolowane parametry jakosci wody nie zmienialy sieistotnie (p < 0.05) w obrebie poszczeg61nych stezen ekstraktu (rye. 1).Przetrzymywanie ryb w ekstrakcie prowadzilo do istotnego (p < 0.05) zahamowaniawzrostu ryb. Ryby kontrolne umieszczone w wodzie bez ekstraktu wykazywalyprzyrost ciezaru wynoszacy 12,84 g. Przyrost ciezaru ryb przetrzymywanych wekstrakeie wynosil: 4,51, 6,13, 7,33, 9,20 i 9,39 g odpowiednio dla malejacych stezenekstraktu - 1,56, 0,78, 0,39, 0,19, 0,09 mg dm-3 (rye. 2). Ryby przetrzymywane wekstrakcie w stezeniach 1,56 i 0,78 mg -3 wykazywaly nienaturalne zaehowanie.Wplyw nizszych stezen na zachowanie ryb byl minimalny. Nie zaleca sie stosowaniaekstraktu z A indica przez lokalnych rybak6w, gdyz stala obacnosc ekstraktu w

wodzie powoduje zahamowanie wzrostu ryb.

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