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Studies on the population dynamics of cichlid fish species in Opi lake were carried out between August, 2014 and January, 2015. Also, physico-chemical parameters of the lake were analyzed using appropriate methods. Morphometric relationships and seasonal variations of the fish species were determined. A total of 235 cichlid fish, comprised of 5 species, namely: Tilapia zillii (28.09%), Sarotherodon melanotheron (51.49%), Oreochromis niloticus (14.04%), Pelmatochromis guentheri (5.96%) and Hemichromis fasciatus (0.43%) respectively were sampled and used for the study. The above listed cichlid fishes showed no correlation (P>0.01) and (P>0.05) with values of the physico-chemical parameters determined. S. melanotheron however, showed positive correlation (P<0 .05="" all="" except="" females="" fish="" gonads="" i="" in="" males.="" more="" much="" phosphate.="" recorded="" ripe="" sampled="" showed="" species="" than="" that="" the="" there="" were="" with="">O. niloticus
where mature gonads were greater in number. In T. zillii, the smallest sexually matured females were 8.1 cm total length. The length–length relationship had a b–value of 0.76 when compared to the length–weight (L-W) relationship that showed positive allometric growth of b>3. Growth parameters of T. zillii showed asymptotic length of L¥ = 1.27 cm Tl, growth curvature (K) = 0.8 yr-1, growth performance index Q1 = 0.11, age–at–length zero (to) = 0.48 yr and the higher potential longevity (tmax) = 3.75 yrs. Mortality parameters showed that the total mortality (Z), natural mortality (M), fishing mortality (F) and exploitation rate (E) were 3.36 yr-1, 1.755 yr-1, 1.605 yr-1 and 0.48 yr-1 each. The smallest sexually matured female in S. melanotheron was 9.8 cm Tl. The length-length relationship had a b–value of 0.79 and L–W relationship showed positive allometric growth of b>3. The growth parameters showed that L¥ was 37.38 cm Tl, K = 0.8 yr-1, Q1 = 3.1, to = 0.188 yr and tmax = 3.75 yrs. Also, mortality parameters showed that Z = 4.54 yr-1, M = 0.70 yr-1, F = 3.34 yr-1 and E = 0.85 yr-1 respectively. O. niloticus had sexually matured female of 11.5 cm Tl. Whereas length-length relationship gave a b–value of 0.82 while L–W relationship showed positive allometric growth of b>3. Bertalanffy growth parameters were L¥ = 5.27 cm Tl, K = 0.8 yr-1, Q1 = 1.35, to = 0.32 yr and tmax = 3.75 yrs. Mortality estimate were Z = 3.39 yr-1, M = 1.175 yr-1, F = 2.21 yr-1 and E = 0.65 yr-1 respectively. Also P. guentheri had sexually matured female of 11.6 cm Tl. Length-length relationship had a b–value of 0.84 and L–W relationship showed negative allometric growth of b<3 .="" bertalanffy="" growth="" i="" parameters="" the="" were="">L¥ = 22.0 cm Tl, K = 0.8 yr-1, Q1 = 2.59, to = 0.22 yr and tmax = 3.75 yrs. Mortality estimates were Z = 2.6 yr-1, M = 0.80 yr-1, F = 1.80 yr-1 and E = 0.21 yr-1. H. fasciatus was only sampled once towards the end of the study (January) which showed that the species appear endangered. Fishing mortality was substantially high in all the species sampled which is undesirable since it can lead to the collapse of the cichlid fish species in Opi lake.


Title Page
Table of Contents
List of Figures
List of Tables
List of Plates

1.1       Introduction
1.1.1    Justification of the study
1.1.2    Objectives of the study
1.2       Literature Review
1.2       Life cycle
1.3       Physico-chemical parameters
1.4       Biological properties
1.5       Growth parameters
1.6       Mortality parameters and exploitation
1.7       Predator-prey relationship
1.8       Economic importance
1.9       Recruitment
1.10     Overfishing

2.1       Study Area
2.2       Meteorological Data
2.3       Sampling Methods
2.4       Experimental Design
2.4.1    Morphometric relationships
2.4.2    Growth parameters
2.4.3    Size/age at sexual maturity
2.4.4    Longevity
2.4.5    Estimation of mortality coefficients
2.4.6    Exploitation rate
2.5       Statistical Analysis
2.6       Physico-chemical Monitoring

3.1       Meteorological Parameters
3.2       Correlation matrix and Physico-chemical Parameters of Opi Lake
3.2.1    Monthly variation of physico-chemical parameters of Opi lake
3.2.2    Seasonal variation of physico-chemical parameters of Opi lake
3.2.3    Correlation of cichlid fish species and physico-chemical parameters of Opi lake
3.3       Population Structure and Monthly Variation of Cichlid Fish species
3.4       Reproduction
3.4.1    Tilapia zillii
3.4.2    Sarotherodon melanotheron
3.4.3    Oreochromis niloticus
3.4.4    Pelmatochromis guentheri
3.5       Morphometric Relationship
3.5.1    Length–length relationship
3.5.2    Length–weight relationship
3.6       Growth Parameters
3.7       Mortality Parameters
3.8       Exploitation Parameters

CHAPTER FOUR: Discussion


1.1    Introduction and Literature Review
Cichlid fishes belong to the family Cichlidae, in the order Perciformes. The family is both large and diverse, and at least 1,650 species have been scientifically described by Froese and Daniel (2012), making it one of the largest vertebrate families. The actual number of species is therefore unknown with estimates varying between 2,000 and 3,000 (Stiassny et al., 2007). Cichlids belong to the sub order Labroidei, along with the wrasses (Labridae), Damselfishes (Pomacentridae), and Surf perches (Embiotocidae) families (Stiassny et al., 2007). Cichlids are among the most popular freshwater fish kept in the aquarium and are classified by Nelson (2006) as follows:

Kingdom:                 Animalia

Phylum:                    Chordata

Class:                          Actinopterygii

Order:                        Perciformes

Suborder:                Labroidei

Family:                      Cichlidae

Nelson (2006) recognized eight subfamilies of Cichlids: Astronotinae, Cichlasomatinae, Cichlinae, Etroplinae, Geophaginae, Heterochromidinae, Pseudocrenilabrinae and Retroculinae. Sparks and Smith (2004) reported that cichlid taxonomy is still being debated, and classification of the genera cannot yet be definitively given. A comprehensive system of assigning species to monophyletic genera is still lacking, and there is no complete agreement on what genera should be recognized in this family (Nelson, 2006). Some of the most well known cichlid species are Angelfish, Oscar, Jack Dampsey and Discus (Stiassny and Lamboj, 2010).
The different cichlid species have developed in diversity in other to fit their own specific niches, and different cichlid species can therefore vary significantly when it comes to size, temperament (natural behavior), feeding habit, preferred water quality (Froese and Daniel, 2012).

Cichlids live in fresh and brackish waters and can be found in Asia, Africa and South of 300 N in American (Helfman et al., 1997). Several species of Tilapia, Sarotherodon and Oreochromis can disperse along brackish coastlines between rivers (Loiselle, 1994). Frank (2005) reported that most extreme habitat for cichlid fishes are the warm hypersaline lakes, where members of the genera Alcolapia and Danakilia are found. Lake Abaeded in Eritrea encompasses the entire distribution of D. dinicolai, and its temperature ranges from 29 - 45oC (Stiassny and Lamboj, 2010; Norlander, 2009; Graves et. al., 2002).

Population dynamics is a change in the number of fishes in a population or the vital rates of a population over some time. Enyenihi et al. (1986) reported that a good understanding of fish population dynamics (i.e., how mortality, growth and recruitment interact to affect abundance) is required to inform fisheries management on sustainable yield on the case of the endangered Kootenai River white sturgeon (Acipenser transmontanus).

Growth and Mortality rates have been studied in selected species but because of the very high degree of speciosity, dynamic pool model cannot be satisfactorily applied to demersal stocks (Oliver, 1999). Also, Oliver (1999) stated that demersal fisheries exploit a number of species which are so evenly mixed on the fishing ground that it is difficult to single out individual species as dominant.

Scientific understanding of population dynamics and stocks status are entirely fishery-dependent i.e. independent research surveys are not used to monitor their populations (Graves and Macdowell, 2006). Therefore, estimates of historical biomasses are based on the relative measures of catch per unit of effort (CPUE) obtained which are assumed to be proportional to exploitable abundance, because the populations are not sampled at random, unbiased fashion. A complete reliance on fishery-dependent data may introduce many potential sources of error. However, CPUE time series and assessment models fitted to CPUE data are currently the best available estimates of historical relative abundance (Graves and Macdowell, 2006). Tobler (2005) stated that despite a potential promising trend in recent years for white marlin (Parachromis friedrichsthalii), the relative biomasses estimated for each species have declined substantially from 70–50% level. Stiassny et al. (2007) noticed that when Lake Turkana was raising the shoals of Tilapia ‘dispersed’ and the yield was little, he called the period of inundations “off season”, and usually did not fish from August to December.

Seasonal dispersion of Tilapia associated with inundation has been observed in a Sudan floodplain (Hickley and Baily, 1987; Baber et al., 2002) and in Lake Mweru (Reid, 1990), and according to Sparre and Hart (2002), there are regular seasonal variations in catches of cichlid fish species in the East African Great Lakes, generally with decreased catches in drier....

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