A study of the length at maturity and hooks/gill net mesh selection in Clarias lazera from Lake Chad

The minimum length at first maturity of Clarias lazera was found to be 24 cm (4.8%) for females and 20 cm (1.8%) for males. Fifty percent maturity was attained at length of 28 cm to 30 cm for both sexes; there being little difference among the sexes at this level of maturity. The modal retention lengths for gill nets were: 13 cm for 25.5 mm mesh; 18 cm for 32 mm mesh; 28 cm for 57 mm mesh; and 38 cm for 76 mm mesh. Modal lengths of Clarias lazera caught by various hooks sizes were No. 10 (28 cm); No. 11 (33 cm); Nos. 15 and 16 (28 cm). It is recommended that to protect the clarias fishery in Lake Chad, the use of gill nets of less than 57 mm mesh size and fishing hook No. 16 (and smaller sizes) which caught 43.94% of immature fishes should be discouraged

Commercial production of natural freshwater fish food

A review is made of some of the methods that can be used for mass cultivation of natural fish food and the types of organisms that are cultured, which include various algae and zooplankton. Some examples are given of successful case histories in the mass cultivation of natural fish food in order to stimulate the interest of Nigerian scientists on research activities of live fish food for use by fish farmers in the country

The influence of some environmental variables on the apparent abundance of skipjack tuna, Katsuwonus pelamis, in the Eastern Pacific Ocean

ENGLISH: The abundance of skipjack larvae in the central and western Pacific approximately doubled for every 1°C increase in sea-surface temperature (SST) from 23°C to a maximum of about 29°C, and then usually decreased with further increases in SST. Skipjack larvae are scarce in the eastern Pacific Ocean (EPO), so most skipjack recruits and adults in this area are believed to have originated in the central and, possibly, the western Pacific. The catch per unit of effort (CPUE), in short tons per day's fishing, and the catch rate, in number of fish per day's fishing, are estimates of apparent abundance in a fishery. The logarithm of the annual CPUE for skipjack for international baitboats in the EPO for the 1934-1960 period was positively correlated with SST in the spawning area in the central Pacific 18 months earlier (r2 0.31), during the July-June period when most of the recruits in each cohort were presumed to have been spawned. Adequate data for other environmental variables were not available for testing with the baitboat data. The other environmental variables available and selected for testing for correlation with estimates of skipjack abundance for purse seiners for the 1961-1984 period and the reasons for their selection are as follows. 1)Wind-mixing index (WMI). The degree of mixing in the upper layers of the ocean is proportional to the cube of the wind speed, called WMI. The degree of mixing in the spawning areas of the central and the western Pacific may affect the concentration of organisms that skipjack larvae feed upon, thereby influencing their survival, and ultimately determining cohort strength and the number of recruits to the eastern Pacific fishery. 2) SST in the fishing areas at the time of fishing (SST). The CPUE for yellowfin tuna has been shown to be inversely related to SST in the fishing areas, and there are indications that skipjack CPUE is lower during EI Nino events when SST is higher than normal. 3) North-south SST gradient across the thermal front off the Gulf of Guayaquil. This is a measure of the degree of upwelling and nutrient enrichment of the upper waters south of the front and ultimately of the production of food for tunas. 4) Speed of the North Equatorial Countercurrent (NECC). Young skipjack may migrate from the central Pacific to the EPO in the eastward flowing NECC; if so, the number of recruits might be affected by variations in the speed of the current. The logarithm of the annual catch rate of skipjack recruits by international purse seiners in the EPO for the 1961-1984 period was positively correlated with SST in the spawning area of the central Pacific 18 months earlier (r2 = 0.21),and inversely correlated with WMI in the spawning area 18 months earlier (r2 0.46). The logarithm of CPUE for purse seiners in the area off the Gulf of Guayaquil was not correlated with SST in the spawning area 18 months earlier, but was inversely correlated with WMI in the spawning area 18 months earlier (r2 = 0.19), and inversely correlated with the north-south SST gradient in the fishing area at the time of fishing (r2 0.32). Neither of these estimates of apparent abundance from purse seiners were correlated with SST in the fishing areas, or with the speed of the NECC at earlier times. SPANISH: La abundancia de larvas de barrilete en el Pacífico central y occidental se multiplicó por dos, aproximadamente, por cada aumento de 1°Cen la temperatura de la superficie del mar (TSM) entre 23°C y un máximo de unos 29°C, y luego generalmente disminuyó con más aumentos en la TSM. Las larvas de barrilete son escasas en el Océano Pacífico oriental (OPO), y por lo tanto se cree que la mayoría de los reclutas y adultos en esta zona surgieron del Pacífico central, y posiblemente también del Pacífico occidental. La captura por unidad de esfuerzo (CPUE), en toneladas cortas por día de pesca, y la tasa de captura, en número de peces por día de pesca, son estimaciones de la abundancia aparente en una pesquería. El logaritmo de la CPUE anual de barrilete lograda por barcos de carnada en el OPO en el período 1934-1960 se correlacionó positivamente con la TSM en la zona de desove en el Pacífico central de 18 meses antes (r2 = 0.31), durante el período de junio-julio en el cual se cree que nació la mayoría de los reclutas en cada cohorte. No se dispuso de datos suficientes sobre otras variables ambientales para comprobarlos con los datos de los barcos de carnada. Las demás variables ambientales disponibles y seleccionadas para someterlas a pruebas de correlación con las estimaciones de la abundancia del barrilete de barcos cerqueros en el período 1961-1984, y las razones por su selección, son las siguientes: 1) Indice de mezcla por el viento (IMV). El grado de mezcla en las capas superiores del océano es proporcional al cubo de la velocidad del viento, llamado IMV. Es posible que el grado de mezcla en las zonas de desove del Pacífico central y occidental afecte la concentración de los organismos que alimentan a las larvas del barrilete, afectando así la supervivencia de éstas, y finalmente determinando el tamaño de las cohortes y el número de reclutas a la pesquería del OPO. 2) TSM en la zona de pesca al realizarse la pesca (TSM). Se ha mostrado que la relación de la CPUE del atún aleta amarilla a la TSM en la zona de pesca es inversa, y existen indicaciones que la CPUE de barrilete es inferior durante eventos del Niño, cuando las TSM son superiores a lo normal. 3) Gradiente norte-sur de las TSM a través del frente térmico frente al Golfo de Guayaquil. Esto es una medida del grado de afloramiento y enriquecimiento nutritivo del nivel superior de las aguas al sur de dicho frente, y finalmente de la producción de alimento para los atunes. 4) La velocidad de la Contracorriente Ecuatorial del Norte (CCEN). Es posible que los bariletes juveniles migren del Pacífico central al Pacífico oriental en la CCEN, que fluye hacia el este; de ser así, es posible que la cantidad de reclutas se vea afectada por variaciones en la velocidad de la corriente. El logaritmo de la tasa anual de captura de reclutas de barrilete por cerqueros de varias banderas en el OPO en el período 1961-1964 estuvo correlacionado de forma positiva con las TSM en la zona de desove del Pacífico central de 18meses antes (r2 0.21),y de forma inversa con el IMV de la zona de desove de 18 meses antes (r2 0.46). El logaritmo de la CPUE de los cerqueros en la zona frente al Golfo de Guayaquil no estuvo correlacionado con las TSM en la zona de desove de 18 meses antes, pero sí estuvo correlacionado de forma inversa con el IMV en la zona de desove de 18 meses antes (r2 0.19),y con el gradiente norte-sur de las TSM en la zona de pesca al realizarse la pesca (r2 0.32). Ninguna de estas estimaciones de abundancia aparente provenientes de barcos cerqueros estuvo correlacionada con las TSM en las zonas de pesca o con la velocidad de la CCEN en épocas anteriores. (PDF contains 140 pages.)

Food and feeding habits of Tilapia zilli (Pisces: Cichlidae) in Ondo State University fish farm

The food and feeding habits of Tilapia zillii in the fish farm of Ondo State University, Akungba - Akoko, Nigeria, were studied by gut analysis. Examinations of 150 specimens showed that Nymphea formed the main bulk of food consumed. Spirogyra, Pithophora and Compsopogon occurred frequently while Pistia detritus and plant remains featured less frequently. Variation in the frequency of occurrence of the various food items was observed among the various sizes of samples. The samples within the middle - size group fed on both higher plant and filamentous algae while the young and higher fish consumed exclusively filamentous algae. On the basis of food items found in the gut, Tilapia zillii was classified as primary consumers

Design and selection tools for sports equipment

This report presents work from the first nine month of a project investigating design methodologies and selection tools to promote innovations in sports equipment. Particular consideration is given to product design improvements and new market adoption of advanced materials and processes. Our aim is to couple appropriately similar technologies so as to provide a method of transfer between sports equipment designs. We would like to make barriers between isolated sports equipment markets more transparent without releasing proprietary information. A brief history of sports equipment design is included; issues particularly relevant to material and process technologies are outlined for sports equipment. A start has been made on a software program to express most of this information in a concise and accessible format. The methodology is reviewed with some industrial case studies. There is a need for further research to extend and address the design issues raised in this document; a suggested research programme is attached.

Food composition and digestive enzymes in the gut of the African electric catfish Malapterurus electricus (Gmelin 1789) (Malapteruridae)

Analyses of stomach contents of 330 Malapterurus electricus (standard length, 10.1-30.5 cm) in Mahin Lagoon (southwestern Nigeria) established it as a bottom feeder. There was a preponderance of insects accounting for >80% occurrence and >25% of total volume in stomachs of specimens, suggesting a stenophagous predatory habit. Qualitative and quantitative assays of digestive enzymes in the different regions of the gut (oesophagus, stomach, duodenum, ileum, rectum) were investigated. Carbohydrases (amylase, maltase), chitinase, proteases (pepsin, chymotrypsin, trypsin) and lipases were detected in different gut regions with different activity. The pattern of distribution and relative activity of the enzymes correlated with the predatory diet

Absorption of food in the black-jaw tilapia, Sarotherodon melanotheron (Ruppell) from a small tropical man-made lake in Ibadan, Nigeria

The carbohydrate, protein and lipid contents of the food ingested and their absorption in the intestine of Sarotherodon melanotheron inhabiting Awba lake in Ibadan, Nigeria, were investigated. Total carbohydrates of the ingested food ranged from 39.33 to 55.38% (mean = 48.70% while total protein and total lipid ranged from 10.10 to 17.13% (mean = 12.91%) and 7.79 to 8.96% (mean = 8.28%) dry weight, respectively. Calculated total percentages absorbed were 54.86-62.01 (mean 58.07) carbohydrates 47.33-54.06 (mean = 50.43) protein and 43.27-52.23% (mean 46.56) lipid. Absorption of protein and carbohydrate occurred mostly in the fore-gut (the first one-third of the intestine), while lipid was mostly absorbed in the mid-gut (the second one-third of the intestine). Dietary carbohydrate, protein and lipid contents of the food as well as the absorptive capacity of the intestine for these components of the food varied with size of fish

An investigation of the effect of replacing fish meal with soyabean meal, groundnut cake and blood meal at varied proportion on growth and food utilization of the Clarias anguillaris fingerlings fed in outdoor hapas

Fingerlings of Clarias anguillaris obtained from a homogenous source through induce breeding and each with a mean weight of 2.8g were stocked in ten hapas each measuring 1.0x1.0m in outdoor concrete tank and were fed for eight (8) weeks. Results shows that the best growth rate was recorded among fingerlings fed fish meal as the only protein source (TD5) while DT2 containing soya bean, groundnut cake (40%), blood meal as the protein sources came next. The growth rate of fingerlings fed DT2 (40 % groundnut cake, 10% soyabean meal and 10% blood meal) was higher than those fed DT4 containing 10% fish meal but lower than those fed DT5 which has fish meal as its sole source of protein (53.0%). Analysis of various growth parameters like SGR, FCR and PER. shows that DT5 was the overall best diet but there was no significant statistical difference in weight gained by fish fed the five diets (P <0.05)

Nutritional habits and food consumption pattern of fishing communities around Lake Kainji, Nigeria

The findings are presented of a nutrition survey carried out in the framework of the Nigerian-German Kainji Lake Fisheries Promotion Project in March/April 1995. The major aim of the study was to obtain closer information on the food habits and food consumption patterns of the fishing population, especially the quantification of fish and small fish in particular, consumed at the household level. A standardized questionnaire was used to collect relevant information on demographic, education and occupational profiles; the information was collected in 39 villages in the southern sector of Kainji Lake. (PDF contains 75 pages)