Age and Growth of Oreochromis Niloticus (Pisces:Cichlidae) in Lake Hayq, Ethiopia
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Date
1995-06
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Addis Ababa University
Abstract
otoliths from 447 mature and 308 immature Oreochromis
niloticus (10 to 304 mm total length) from Lake Hayq were
measured and examined for translucent and opaque macrozones.
Microzone analysis was also conducted on the 308 immature
O. niloticus otoliths. Macrozonal daily age estimate was
determined by extrapolating the number of days between the
date of capture and calender birth dates. utilization of the
number of macrozones, condition on the edge of otoliths and
date of capture enabled the separation of fish into
recruitment groups. Microzones on the otoliths were
enumerated and used as a measure of age in days and to hind
cast hatch dates. The relationship between otolith size and
fish total length 11as also examined.
It appears that the breeding of o.niloticus in Lake Hayq is
continuous with high peaks during !·larch-May and July-October.
Two translucent macrozones '''ere formed per year during
January-February and June-July. Fish spa~ned between January
and May and July and November of the same year form the first
translucent zone associated with biannuli at different times.
The close agreement between macrozonal and microzonal daily
age estimates (r=O. 84) sUbstantiates the usefulness macrozone
analysis to assess the age of O.niloticus. There was a strong
linear relationship between otolith size and fish size and
also between microzone count and fish length. HOI-leVer, a
linear relationship underestimates fish size at later ages.
Values of size-at-age estimates obtained from macro zone and microzone analysis and fish total length-otolith radius
relationship were close to each other. This demonstrates the
usefulness of results from the latter method in supporting
conclusions drawn from macrozone and microzone analysis.
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Biology