Basic aspects of the biology of Ilisha africana caught at Down beach Limbe.

ABSTRACT

This study examined some aspects of the biology of Ilisha africana at down beach Limbe. Samples collected from artisanal fishers, were stored in an ice cooler and quickly rushed to the laboratory where specimens were closely observed and data recorded.

Major findings, recorded for combined sexes mean values of 0.75, 9.66, 1.05:1 and a=0.02; b=2.57 for condition factor, gonad somatic index, sex ratio and length weight relationship coefficients respectively.

The results indicate that growth conditions are unfavorable for I. africana, as it experiences allometric growth (negative, b<3).

Sex ratio and gonad somatic index suggest that spawning period could be during the month of April for this species. This demonstrates that caution should be taken while handling this fish in that ecosystem to ensure sustainability

CHAPTER 1

INTRODUCTION

1.1 Background

Fish is a source of highly nutritive protein and also contains other essential nutrients required by the body. Fishes are the most harvested food source from natural; hence studies on fish biology are essential for sustainable management and conservation of fish biodiversity. In addition, fishes exist at or near the top of the food chain and can serve as an indicator of the condition in an aquatic ecosystem (Negi and Maimgain, 2013).

Ilisha africana, the species of interest in this study is of the family Pristigasteridae; very abundant in West African waters from Senegal to Angola (King, 1991). It is an estuarine species of marine origin. Ilisha africana spends part of its life cycle in the estuary mostly feeding or breeding.

Lizamaa et al. (2002) highlighted that knowledge of biometric (quantitative) aspects such as length-weight relationship, condition factor: relative well being of a fish species in an ecosystem, growth and mortality of fishes are tools necessary for studies in fish biology.

Length-weight relationship key is a classical method that has been useful in monitoring the current population and condition also estimating weight from length measurements during yield assessment. In fisheries science, the condition factor is used in order to compare the condition, fatness or wellbeing of fish (Ighwela et al., 2011). Furthermore condition factor is also a useful index for monitoring of feeding intensity, age and growth rates in fish (Ndimele et al., 2010).

Abobi and Ekau (2013), reported that condition factor defines the state of wellbeing of the fish and reflects through variations, some information on the physiology of the fish, and it is assumed that the higher the value of condition factor, the better the state of wellbeing.

Knowledge of reproductive biology of fish is essential for evaluating the commercial potentialities of its stock, life history, culture practice and management of its fishery (Dopeikar et al., (2015)) showed variation in size structure of 12-24cm and 15-23cm for samples collected from sea and estuary respectively, suggesting that the small and large size (variations) could be due to conflicting oceanographic parameters (e.g salinity) as the Saloum estuary has been reported by Amponsah et al. (2021) to have salinity rates quadruple that of the sea. Faye et al. (2017) pointed out that  high salinity rates could be a challenge to the well being of Ilisha africana juveniles and with the issue of climate change capable of impacting salinity, it is important to monitor the condition (factor) of the ecosystem, fish especially those susceptible to salinity fluctuations so as to keep benefiting from marine ecosystems resources  and services.

1.2 Statement problem

-Information about some aspects of  the biology of Ilisha africana  including spawning, health and growth pattern are scarce in the coastal and marine ecosystems of Cameroon.

1.3 Hypothesis:

• Null: Ho- growth of Ilisha africana at Down Beach, Limbe is allometric.

• Alternative: HA- growth of Ilisha africana at Down Beach, Limbe is isometric

1.4 Justification

• It is necessary to estimate the biomass of Ilisha africana population, from length observations.

• It is important to assess the wellbeing of Ilisha africana at down beach, Limbe.

• Forecast africana growth in weight, from growth in length equations.

• Evaluate how external factors; physiological and environmental can influence diet, consequently size of Ilisha africana at Down Beach, Limbe.

1.5 Objectives

1.5.1 Main objective

This study aimed to examine some basic aspects of the biology of Ilisha africana caught at Down beach Limbe.

1.5.2 Specific objectives

To determine:

-Length Weight relationship and condition factor of Ilisha africana

-Gonadsomatic index (GSI) of Ilisha africana.