A review of length-weight relationship and its parameters in aquatic species

Length weight relationship and its parameters are requiring in practical assessment of stocks of aquatic species. The exponent b describes the growth condition of the species in question. If the value of b is 3 around 3, the fish is said to exhibit isometric growth if the value of b is less or greater than 3 the species is said to exhibit isometric growth if the value of b is less or greater than 3 the species as exhibiting both isometric and allometric conditions. Such conclusions are erroneous and misrepresentation of scientific facts. They stem from the use of inappropriate methods in estimation of the LW parameters and the authors? lack of understanding of the biological theory behind the growth conditions. To correct these erroneous presentations, the paper highlights the appropriate approach for the estimation of the LWR parameter. Large sample size. Wide size range and appropriate statistical tools are essential ingredients for accurate estimation of the LW parameters. The paper also elucidates on the concept of isometric and allometric growth in fishes and other invertebrates. A minimum of one year time scale of data collection in order to capture all the size ranges, from the young of the year to the oldest individual in the population, so as to reflect the ontogenetic growth performance of the aquatic species, have been propose

Factors influencing the emigration of juvenile Bonga from the Cross River estuary

Studies were conducted to identify and quantify the proximate factors responsible for the emigration of juvenile bonga Ethmalosa fimbriata (Bowdich, 1825) from the Cross River estuary. A time series of bonga cpue, salinity, turbidity and plankton abundance was undertaken, juvenile bonga was abundant in the estuary when salinities ranged between 1 and 9ppt. at salinities outside this range, they were absent. We conclude that salinity is the proximate factor that initiates the emigration of juvenile bonga from the estuar

A comparative study of the decomposition of Rhizophora racemosa and Nypa fruticans of the great Kwa River, Cross River State, Nigeria

Mangroves are specialized marine ecosystem which is highly productive. They act as shelter, breeding and nursery grounds for a variety of Marine and brackishwater invertebrates and fishes. Some of the dominant plant species in mangrove vegetation of Nigerian coastline are Rhizophora species and Nypa fruticans. Studies were conducted on the decomposition of Rhizophora species and N. fruticans. The objective was to compare their decomposition rates and proffer informed management decisions. Decomposition rates of the two were monitored for 112 days using litter box experiment. Eight litter boxes were stocked with 10g of leaves of each species and two boxes containing the respective plants species were removed and examined for dry matter, carbon and nitrogen contents. There was no significant difference in the rates of decomposition of Rhizophora and N. fruticans leaves (p~.0.05) even though N. fruticans showed slightly higher rate of decomposition than Rhizophora. The linear relationship between the loss in dry matter and number were expressed as Y= 10.1-0.080x in N.fruticans, and Y=9.0-0.073x in Rhizophora sp. It was concluded that the argument in favour of the eradication of N.fruticans for the thriving of Rhizophora is inaccurate. Containment of the population rather than control is the logical strategy for the management of the riparian vegetation in the face of climate change

Proximate analysis of snakehead fish, Parachanna obscura (Gunther 1861) of the Cross River, Nigeria

African snakehead, Parachanna obscura is being considered as an emerging aquaculture candidate in Nigeria. The species is very palatable and has a good fillet quality. Study was conducted on the proximate composition of the species from Cross River, Nigeria. Samples of snakehead were analyzed for protein, fat, moisture, crude fibre and ash contents. The protein content of the species ranged from 21.03-22.03 with mean value of 21.5%. The fat content ranged from 17.1-17.4% with a mean value of 17.2 %. Moisture content ranged from 51.1-52.0 % with a mean value of 51.7%. Ash and crude fibre contents were very low. The protein content of Parachanna obscura compares favourably with that of other members of the family Channidae. The fat content is exceptionally high, making the species a good healing and recuperating agent for post-natal and post-operation patients. We strongly recommend the culture of Parachanna obscura in Nigeria and its meal for growing children

Fecundity, gonadosomic index and spawning period of Chrysichthys nigrodigitatus of the Lower Cross River, Nigeria

The estuarine catfish, Chrysichthys nigrodigitatus, is a prized food fish in Nigeria especially in the Niger Delta region. There is a growing concernrn over the sustainability of the fishery in the face of climate change and environmental variability. Studies were conducted on the fecundity, gonadosomatic index and the spawning period of the species. The objectives were to determine the average fecundity of the species and to use the gonadosomatic index to determine its spawning period with the aim of proffering management advice and prerequisites of the species in the face of climate change. A total of 44 females and 40 males were used for the study which spanned the period from May 2011 to April 2012. The fecundity of the species ranged from 3,730.5 eggs to 41,535.9 eggs. There was correlation between the total fecundity and fish weight (p~,01, r= 0.80, n= 44). The regression model for the relationship was expressed as fecundity = 4660.8+4.76 weight. The gonadosomatic index was highest in the month of May and dropped sharply in june signifying that spawning in Chrysichthys nigrodigitatus starts around this period. The implications of these findings in respect to sustainability of the species, and its aquaculture in the face of climate change are discussed

Reproductive efficiency as a function of age in estuarine catfish, Chrysichthys nigrodigitatus of the Cross River, Nigeria

Study was conducted on the reproductive efficiency of Chrysichthys nigrodigitatus of the Cross River. The objective was to determine the influence of age on eggs size and fecundity. Forty four females of Chrysichthys nigrodigitatus were sampled from April, 2011 to March, 2012. Fecundity and eggs size were measured in relation to fish size. The relationship between egg size and fish size produced a parabolic curve. This implies that younger fish and older fish were less efficient in terms of eggs size and quality while the middle aged fishes were more efficient in terms of eggs size and quality. Similarly, there was an inverse curvilinear relationship between number of eggs per unit weight and somatic weight of the fish. Younger fish are less efficient because of the physiology of growth, while the older fishes are less efficient because of reproductive senescence. Management strategy for the stock therefore requires the conservation of the middle aged individuals for increase in reproduction. Also in aquaculture the middle aged class should be used as broodstock for excellent results

Elemental concentration and size relationship in African cuttlefish Sepia bertheloti, from the coastal waters of Qua Iboe River, Nigeria

Ten specimens of African cuttlefish, Sepia bertheloti, from the coastal waters off Qua Iboe River, Southeast Nigeria, were analyzed for the relationship between the concentration of the elements and the size of the species. Energy Dispersive X-ray fluorescence technique was employed to determine the elemental composition of the species. Eleven elements were identified in the body of cuttlefish. These were Chlorine, Strontium, Potassium, Calcium, Bromine, Iron, Copper, Zinc, Manganese, Nickel and Selenium of these elements, the concentration of calcium, potassium. Copper and strontium had a positive correlation with the weight, while the concentrations of manganese, nickel, chlorine, iron were negatively correlated with their weights. However, only manganese had a significantly negative correlation (p<0. 05). Bromine and zinc had no correlation with the weights of the species. There also existed a significant positive correlation between Ca and K, Se and Ni, Cu, Br and Zn and St and K. We conclude that African cuttlefish, irrespective of size is a rich source of nutritional elements and is especially recommended for pregnant women and for all age groups

The current rate of exploitation of Bonga by the purse seine fishery in the Cross River Estuary and adjacent coastal waters, Nigeria

Studies were conducted to assess the current level of exploitation of bonga in Cross River Estuary and its adjacent coastal waters. Time series of length-frequency distribution of bonga over 18 months time scale was carried out. FAO-ICLARM Fish Stock Assessment Tool (FiSAT) was employed to determine the population and growth parameters. The instantaneous rates of total mortality,fishing mortality and natural mortality were 6.9 per year, 5.30 per year, and 1_61per year respectively. The exploitation rate was 0.77. This implies that the stock of Efimbriata of Cross River Estuary is experiencing excessive fishing pressure. This proposition is accentuated by the downward trend in bonga abundance throughout the study period. The over fishing is attributed to the Ghanaian purse seining, which even penetrates into the bonga nursery in the inner Cross River estuary for destructive fishing. This phenomenon has exerted adverse socio-economic impact on thelife of the people of lower Cross River basin whose main source of livelihood is bonga fishery. We propose a ban on the purse seine fishery in Cross River Estuary

Fecundity, gonadosomatic index and size at maturity of Bonga Ethmalosa Fimbriata in the costal waters off the cross river Estuary, Nigeria

No Abstract. Global Journal of Pure and Applied Sciences Vol. 12(3) 2006: 287-29

Length-weight parameters and condition factor of Bonga, Ethmalosa fimbriata in the Cross River Estuary, Nigeria: importance of large volume of data

No abstract available Length-weight parameters for bonga, Ethmalosa fimbriata in Cross River Estuary were estimated. Weight growth in Ethmalosa fimbriata was found to be isometric, with exponent b= 3.0 and a = 0.00967. This indicates that growth is proportional in all directions. The value of (a) was the same as that of the condition factor, providing a biological interpretation to the parameters of the length-weight relationship. The importance of using large volume of data in the estimation of the parameters of length-weight relationship in any fish species as well as the implication of these findings with regards to the possibility of applying conventional fish population dynamics models to the analysis of bonga population are demonstrated. Key Words: Length-weight parameters; condition factor; bonga; Cross River Estuary; large data Global Jnl Pure and Applied Sciences Vol.10(3) 2004: 379-38