An evaluation of electrofishing as a control measure for an invasive tilapia (Oreochromis mossambicus) population in northern Australia.

Combating the spread of invasive fish is problematic, with eradication rarely possible and control options varying enormously in their effectiveness. In two small impoundments in north-eastern Australia, an electrofishing removal program was conducted to control an invasive tilapia population. We hypothesised that electrofishing would reduce the population density of Oreochromis mossambicus (Mozambique tilapia), to limit the risk of downstream spread into areas of high conservation value. We sampled by electrofishing monthly for 33 months. Over this period, there was an 87% decline in catch per unit effort (CPUE) of mature fish, coupled with a corresponding increase of 366% in the number of juveniles, suggesting a density-dependent response in the stock-recruitment relationship for the population. Temperature was inversely related to CPUE (r=0.43, lag=10 days), implying greater electrofishing efficiency in cooler months. The reduction in breeding stock is likely to reduce the risk of spread and render the population vulnerable to other control measures such as netting and/or biological control. Importantly, the current study suggests routine electrofishing may be a useful control tool for invasive fish in small impoundments when the use of more destructive techniques, such as piscicides, is untenable.

Reproductive strategies of two invasive tilapia species Oreochromis mossambicus and Tilapia mariae in northern Australia

The reproductive biology of two invasive tilapia species, Oreochromis mossambicus and Tilapia mariae, resident in freshwater habitats in north-eastern Australia was investigated. Oreochromis mossambicus exhibited plasticity in some of its life-history characteristics that enhanced its ability to occupy a range of habitats. These included a shallow, weed-choked, freshwater coastal drain that was subject to temperature and dissolved oxygen extremes and water-level fluctuations to cooler, relatively high-altitude impoundments. Adaptations to harsher conditions included a decreased total length (LT) and age ( A) at 50% maturity (m50), short somatic growth intervals, early maturation and higher relative fecundities. Potential fecundity in both species was relatively low, but parental care ensured high survival rates of both eggs and larvae. No significant difference in the relative fecundity of T. mariae populations in a large impoundment and a coastal river was found, but there were significant differences in relative fecundities between several of the O. mossambicus populations sampled. Total length ( LT) and age at 50% maturity of O. mossambicus populations varied considerably depending on habitat. The LTm50 and Am50 values for male and female O. mossambicus in a large impoundment were considerably greater than for those resident in a small coastal drain. Monthly gonad developmental stages and gonado-somatic indices suggested that in coastal areas, spawning of O. mossambicus and T. mariae occurred throughout most of the year while in cooler, high-altitude impoundments, spawning peaked in the warmer, summer months. The contribution these reproductive characteristics make to the success of both species as colonizers is discussed in the context of future control and management options for tilapia incursions in Australia.

A review of the biology, ecology, distribution and control of Mozambique tilapia, Oreochromis mossambicus (Peters 1852) (Pisces: Cichlidae) with particular emphasis on invasive Australian populations

Oreochromis mossambicus (Peters 1852) are native to the eastward flowing rivers of central and southern Africa but from the early 1930s they have been widely distributed around the world for aquaculture and for biological control of weeds and insects. While O. mossambicus are now not commonly used as an aquaculture species, the biological traits that made them a popular culture species including tolerance to wide ranging ecological conditions, generalist dietary requirements and rapid reproduction with maternal care have also made them a 'model' invader. Self-sustaining populations now exist in almost every region to which they have been imported. In Australia, since their introduction in the 1970s, O. mossambicus have become established in catchments along the east and west coasts and have the potential to colonise other adjacent drainages. It is thought that intentional translocations are likely to be the most significant factor in their spread in Australia. The ecological and physical tolerances and preferences, reproductive behaviour, hybridization and the high degree of plasticity in the life history traits of O. mossambicus are reviewed. Impacts of O. mossambicus on natural ecosystems including competitive displacement of native species, habitat alteration, predation and as a vector in the spread of diseases are discussed. Potential methods for eradicating or controlling invasive populations of O. mossambicus including physical removal, piscicides, screens, environmental management and genetic technologies are outlined.

Estimación de la prevalencia e intensidad de parásitos internos y externos en la Tilapia (Oreochromis nitoticus) en la granja piscícola UNA-ADPESCA, Managua, Nicaragua

El presente trabajo investigativo tiene como objetivo identificar los parásitos internos y externos de la tilapia (Oreochromis niloticus). Esta investigación se llevó a cabo en la Granja Piscícola UNA-ADPESCA, ubicada en las instalaciones de la Universidad Nacional Agraria en el kilómetro 12 ½ Carretera Norte en el Departamento de Managua. Se realizaron varios muestreos en donde se seleccionaron cuatro estanques destinados a cultivo de peces de estadio juvenil donde se escogieron peces al azar para su correspondiente estudio a nivel de laboratorio. Se utilizó un modelo estadístico descriptivo, con el cual se evaluaron las variables de prevalencia, e intensidad del parásito monogéneo y la talla de la tilapia en los meses de Marzo, Abril, Mayo y Jimio del 2.000. El parásito identificado fue el monogéneo (Cichlidogyrus sclerosus) alojado en las branquias de las tilapias. La prevalencia del parásito encontrado en la tilapia, resultó ser mayor en el mes de Mayo debido a que en este mes en la granja existió una sobrepoblación en los estanques de cultivo y esto permitió que mayor cantidad de peces fueran parasitados. La intensidad fue más alta en los meses de Mayo y Junio donde se prestaron las condiciones más favorables para que una cantidad determinada de una misma especie de parásito afectara a los peces, la presencia de estos parásitos en el cultivo de peces fue por el grado de contaminación de la fuente abastecedora de agua y la acción de los depredadores que se encargaron de propagar a los patógenos. En el mes de Junio se trabajó con peces de tallas superiores a los meses de Marzo, Abril y Mayo, esto demostró que peces de gran talla son menos resistentes a la presencia de los parásitos y son susceptibles a una infestación. Las medidas preventivas sanitario profilácticas empleadas en la granja piscícola UNA-ADPESCA demostraron ser eficientes en el control de éstos parásitos, permitiendo así producir peces de buen peso, vigorosos y saludables.

Evaluación del comportamiento productivo de tilapias (Oreochromis niloticus) utilizando cuatro tipos de fertilizantes orgánicos

El presente trabajo se desarrolló dentro del marco del proyecto UNA•IFS, financiado por la lntemational Foundation for Science. Este tuvo como objetivo general: Evaluar cuatro tipos de fertilizantes orgánicos provenientes de cerdos alimentados con concentrado y desperdicios de cocina en la producc1ón de Tilapia (Oreochromis niloticus). Contribuyendo a reducir la contaminación ambiental los siguientes objetivos específicos: l. Evaluar el comportamiento de la ganancia media diaria (G. M.D), peso vivo y talla de las Tilapias producidas en estanques fertilizados con cuatro tipos de fertilizante orgánico. 2. Determinar la relación entre las, variables talla y peso. de acuerdo a los cuatro tipos de fertilizante. 3. Evaluar los parámetros de calidad del agua (OD, pH, T°) en función de los cuatro tipos de fenili.zante orgánico. 4. Evaluar económicamente los cuatro tipos de fertilizantes utilizados en la producción de Tilapia. El experimento se llevó a cabo en la hacienda “ Las Mercedes" de la Universidad Nacional Agraria Se utilizaron cuatro estanques de cemento ya establecidos (4.75x3.55x0.90 m). En cada W10 se sembraron 25 tilapias macho (dos peces/m 1 representc.tdo 2 tilapias; una unidad experimental. El recambio de agua se dio de forma natural. Se midió diariamente –T°, pH, OD. Los muestreos se realizaron cada 14 días. Los tratamientos evaluados fueron: T1= Efluente de biodigestores que procesaron estiércol de cerdos alimentados con concentrado; T2= Estiércol fresco de cerdos alimentados con concentrado: T3= Efluente de biodigestores que procesaron estiércol de cerdos alimentados con desperdicios de cocina; T4= Estiércol fresco de cerdos alimentados con desperdicios de cocina. Las variables e.valuadas fueron: peso. talla G.M.D, Calidad del agua (OD, T°, pH). El ensayo se montó y se analizó como un D.C.A. en arreglo bifactorial donde: Factor A== Periodo o muestreo (cada 14 días;) y Factor B: Tipo de Fertilizante. Los cuatro tratamientos orgánicos evaluados constituyen potenciales fertilizantes para el cultivo de tilapia por su buen comportamiento productivo y económico. Para todas las variables analizadas (peso, talla, GMD) el tratamiento que mejor comportamiento presentó fue el T2.seguido del T4. Asimismo el peso y la talla fueron aumentando conforme el tiempo de muestreo. El peso de las tilapias utilizadas en el ensayo se \lo afectado en un 91 %por el comportamiento de la talla. Todos los parámetros de calidad del agua (0.D, pH y T°), estuvieron dentro de los parámetros recomendados para la producción de tilapias. Económicamente considerando el proceso de los tratamientos, tanto el que procedió de animales alimentados con concentrados como el que procedió de desperdicios de cocina. repor1ó mayores utilidades aplicar el estiércol fresco directamente a los estanques, que al procesarlo por biodigestión. Considerando el origen de los tratamientos, tanto utilizando los efluentes como estiércol fresco. El productor obtiene más utilidades cuando provienen de cerdos alimentados con desperdicios de cocina.

The effects of supplemental feeds containing different protein: Energy ratios on the growth and survival of Tilapia nilotica (Oreochromis niloticus) in brackishwater ponds

A research was conducted in thirty approximately 100 sq.m earthern ponds of the Brackishwater Aquaculture Centre (BAC), College of Fisheries, University of the Philippines, Leganes Iloilo from November 7, 1982 to March 7, 1983 to evaluate the effects of nine supplemental feeds containing different protein: energy ratios on the growth and survival of Tilapia nilotica in brackishwater ponds. Nine supplemental feeds formulated were with protein levels of 20%, 25%, and 30% each at three energy levels of 3,000 kcals; 3,500 kcals; and 4,000 kcals. There was a control treatment with no feeding so that mean weight gain growth rate, feed conversion rate, and survival were determined. Fish fingerlings were acclimated from 0-29 ppt. salinity before the experiment and 20% of fish in each treatment were sampled after every 30 days. Growth rates were significantly different and increased with increasing energy level at the 30% protein feeds but decreased at high energy levels in the 20% and 25% protein feeds. Feed conversion was significantly different due to interaction between protein and energy levels in the feeds, and was better at the 30:3,500 kcals feeds having a feed conversion of 1.55 g. Survival was not significantly different

Commercial mariculture of Oreochromis niloticus using net cages

The culture of tilapia has a long history in Africa. Fossil remains of members of the genus have been found which are about 18 million years old (Fryer and Iles, 1972). Oreochromis niloticus was the subject of detailed observations in Egypt of 5,000 years ago. A bas relief of 2,500B.C. depicts tilapia being reared in ponds in Egypt. However, despite this long history the prolific nature of this fish results in very high populations in pond culture systems. Consequently small size fish are harvested. Several methods have thus been tried to control the excessive reproduction of tilapia in captivity with only partial success. This paper reports how large size tilapia especially O. niloticus averaging at least 150g per piece can be commercially produced using floating net cages in the marine environment

Digestibility and nutrient utilization of soybean milk concentrate based diets in Oreochromis niloticus

The digestibility and utilisation of two fresh soybean milk concentrate based diets, two stale soybean milk concentrate based diets and two Fishman based diets serving as control, at optimal (30%) and suboptimal (20%) protein levels were evaluated in Oreochromis niloticus. The diets were as follows: Diet I (control) - fishmeal based diet at 30% crude protein, Diet II (control) Fishman based diet at 20% crude protein, Diet III - fresh soybean milk concentrate based diet at 30% crude protein, Diet IV - fresh soybean milk concentrate based diet at 20%, Diet V - stale soybean milk concentrate based diet at 30% crude protein, Diet VI-stale soybean milk concentrate based diet at 20%. Dry matter digestibility differed not significantly with variation in diets (P:0.05). A significant variation was recorded in the protein, lipid and ash digestibility. Proteins were more digestible at optimum than suboptimum level. Ash digestibility was lowest of all the nutrients. Variations in the utilisation of the diets in terms of weight gain, specific growth rate, food conversion ration, protein efficiency ration and apparent net protein utilization were insignificant (P: 0.05). All diets compared favourably with the standard control diet Diet I. This findings suggest the suitability of stale soybean milk concentrate utilisation as protein supplements in the diets of late fry Oreochromis niloticus

Digestibility and nutrient utilisation of soybean bran-based diets in Nile tilapia Oreochromis niloticus

The digestibility and utilisation of two soybean bran-based diets and two fishmeal-based diets serving as control, at optimal (30%) and suboptimal (20%) protein levels were evaluated in Oreochromis niloticus. These were Diet I (Control)-fishmeal based diet at 30% crude protein, Diet II (Control) - fishmeal based diet at 20% crude protein, Diet III - hydrolysed Soybean Bran based diet at 30% crude protein, Diet IV - hydrolysed Soybean Bran based diet at 20%. Dry matter digestibility differed insignificantly with variation in diets (P<0.05). There was significant variation in the protein (p 20.05), lipid and ash digestibility. Protein was more digestible at optimum level than sub-optimum level, while lipid and ash digestibility did not vary with their inclusion levels. Variation in the utilisation of the diets was significant (P<0.05) except for survival. It was observed that the best diet was Diet 1, closely followed by Diet II with highest values of mean final weight, specific growth rate, protein efficiency ratio and the apparent net protein utilisation. The high digestibility values of Diets III and IV suggests their inclusion in fish diet to spare protein for growth

The growth and survival rate of Oreochromis niloticus fries fed (private) with varying percentages of Leucaena leucocephala leaf meal based diets

A-ten-week feeding trial was carried out to evaluate the growth and survival rate of Oreochromis niloticus fed with varying percentage levels of Leucaena leucocephala leaf meal based diets. The substitution rates of L.leucocephala leaf meal for groundnut cake in the various diets were 0% - Diet 1, 25% - Diet 2, 50% - Diet 3 and 75% - Diet 4. Ten fries with an average weight of 0.44g were stocked at the rate of 10 fish per bowl and fed at 5% body weight. Diet 1 with 0% inclusion of Leucaena leaf meal gave a significant difference (P>0.05) in growth and survival rate compared with diets 2, 3 and 4. The water quality parameters recorded were appropriate for fish culture