Factors to consider when using native biological control organisms to manage exotic plants

Biological control of exotic plant populations with native organisms appears to be increasing, even though its success to date has been limited. Although many researchers and managers feel that native organisms are easier to use and present less risk to the environment this may not be true. Developing a successful management program with a native insect is dependent on a number of critical factors that need to be considered. Information is needed on the feeding preference of the agent, agent effectiveness, environmental regulation of the agent, unique requirements of the agent, population maintenance of the agent, and time to desired impact. By understanding these factors, researchers and managers can develop a detailed protocol for using the native biological control agent for a specific target plant. . We found E. lecontei in 14 waterbodies, most of which were in eastern Washington. Only one lake with weevils was located in western Washington. Weevils were associated with both Eurasian ( Myriophyllum spicatum L.) and northern watermilfoil ( M. sibiricum K.). Waterbodies with E. lecontei had significantly higher ( P < 0.05) pH (8.7 ± 0.2) (mean ± 2SE), specific conductance (0.3 ± 0.08 mS cm -1 ) and total alkalinity (132.4 ± 30.8 mg CaCO 3 L -1 ). We also found that weevil presence was related to surface water temperature and waterbody location ( = 24.3, P ≤ 0.001) and of all the models tested, this model provided the best fit (Hosmer- Lemeshow goodness-of-fit = 4.0, P = 0.9). Our results suggest that in Washington State E. lecontei occurs primarily in eastern Washington in waterbodies with pH ≥ 8.2 and specific conductance ≥ 0.2 mS cm -1 . Furthermore, weevil distribution appears to be correlated with waterbody location (eastern versus western Washington) and surface water temperature.

Fish production from aquatic weeds

Irrigation in the eleven River Basin Authorities and in particular in the South Chad Irrigation Project and the Baga Polder Project is increasing and demands high yearly investments for aquatic weed control in canals and drains. If the weeds are biologically controlled by the grass carp (Ctenopharyngodon idella Val.), the costs will be turned into profit, particularly when the fish production (resident fish plus grass carp) is harvested and sold for food. The use of irrigation canals and drains for aquaculture in the form of fish polyculture may be a wise step towards increased fish production. This paper highlights the concept of fish production from aquatic weed control and concludes that it is a proven profitable venture in several countries

Selectivity of three aquatic weeds as diet for Nile tilapia (Oreochromis niloticus)

A total of sixty juvenile Oreochromis niloticus (Nile tilapia) were fed three species of aquatic weed, namely Azolla filiculoides (water fern), Elodea sp. and Pistia stratiotes (water lettuce) to determine which of the weeds will be selectively consumed, and preferred of all. A control group of twenty Nile tilapia was fed compounded feed. The selectivity of the weeds was observed based on their utilization as food source, and Azolla filiculoides was found to be highly utilized, followed by Elodea sp. and the roots of Pistia stratiotes. The growth response of the fish to the diets was found to be highest for fish fed compounded feed followed by Azolla filiculoides and Elodea sp., while Pistia stratiotes produced a negative growth trend. It is therefore postulated that Azolla filiculoides and Pista sp. are good feedstuffs for O. niloticus especially when used together with other feedstuffs

Growth performance of exotic Oreochromis niloticus, exotic Oreochromis niloticus fed with pelleted feeds in flow-through system

Local, exotic and hybrid tilapia fingerlings were fed 45% crude protein diet containing 18% fish meal in a flow through system in triplicate and their growth and food utilization observed for 14 weeks. At the end of the study, the hybrid (Exotic Oreochromis niloticus male x Exotic Oreochromis aureus female) fingerlings had higher growth rate and food conversion ratio (FCR) than the other treatments. This was followed by Exotic Oreochromis niloticus fingerlings. The exotic Oreochromis niloticus fingerlings came next while the local Oreochromis niloticus fingerlings were the least in growth performance. The survival rate of the local O. niloticus was however higher than the other treatments

The introduction of exotic fish in Sri Lanka with special reference to tilapia

Introductions of exotic finfish between 1948 and 1953 are reported in this paper, with a brief reference to earlier and later introductions. Exotic fish were introduced principally to develop the potential for aquaculture in fresh and brackish waters in order to increase the availability of fish for rural communities through the biological control of aquatic vegetation. The algal feeding tilapia (Sarotherodon mossambicus) has created a new food industry in inland and brackishwaters. It has supplemented marine fishery production in a community where animal protein intake consists mainly of fish. It is also being cultured in flooded rice fields and used in the control of malaria. This excellent table fish has not had any adverse environmental impact.

Exotic species and genetically modified organisms in aquaculture and enhanced fisheries: ICLARM's position

This article contains a discussion paper on the use of exotic species and genetically modified organisms in aquaculture and enhanced fisheries, together with a summary of ICLARM's (International Center for Living Aquatic Resources Management, Philippines) current position on this important topic.

Toxicity of some organic biocides to exotic carp fingerlings Hypophthalmichthys molitrix (C and V)

A bioassay study was conducted using three organic pesticides to determine their comparative toxicity to fingerlings of Hypophthalmichthys molitrix. There was wide variation in the toxicity of different pesticides with 24 hr LC sub(50) values ranging from 0.000403 to 0.294 mg/l. Endosulfan appeared to be the most toxic, whereas BHC was the least.

Impact of the exotic fish, Oreochromis mossambicus, on the indigenous fishery of Powai Lake, Bombay

Fishes impart the most profound influence on the floral-faunistic characteristics of an aquatic ecosystem. Oreochromis mossambicus, an exotic fish accidentally introduced in the Powai lake, India, caused considerable changes in the growth pattern of Indian major carps, ultimately reducing the productive potential of the lake from 33.0 to 11.9 kh/ha. Powai lake is used exclusively for angling for sport. The angling pressure based on the "creel census" from 1955 to 1976 gives a clear picture of the trends in the fishery therein. A considerable decline, ranging from 171 to 400% in the average weight of Indian major carps was recorded.

A mechanical device for eradication of submerged aquatic weeds

This paper embodies details and method of operation of a mechanical device developed for eradication of submerged aquatic weeds. The economics of operation is also discussed.

Catch assessment of indigenous and exotic carp species of Nasti baor

An investigation on length-weight relationship, length-frequency distribution, catch per unit of effort (CPUE) and stocking and harvesting status of three Indian major carps: rohu Labeo rohita, catla Catla catla and mrigal Cirrhinus mrigala and three exotic carps: silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella) and common carp Cyprinus carpio was carried out in Nasti baor (oxbow lake) for the harvesting season from August to December 1995. The length-weight relationship for six carp species was established for the harvesting months of November and December 1995. The b values for different species respectively for the months of November and December were 2.95 and 2.58 for rohu, 3.06 and 2.98 for catla, 2,84 and 2.90 for mrigal, 2.75 and 2.60 for silver carp, 2.51 and 1.97 for grass carp and 2.38 and 2.50 for common carp. In CPUE study, the CPUE was 0.58 kg/ha/hr while the catch per gear was 0.08 kg/ha/hr/purse-seine. The recovery percentage of mrigal was highest (63.57%) and it was lowest (16.81%) in case of silver carp. The density of submerged macrophytes (Hydrilla, Utricularia, Ceratophyllum and Vallisneria) was highest (4.39 kg/sqm) in November and was lowest (0.76 kg/sqm) in September.

Binding of radio-iodinated gonadotropin to the ovary of exotic carp (Cyprinus carpio Lin.)

Heterologous murrel gonadotropic hormone (m-GtH) binds to common carp oocyte plasma membrane and enhances steroid secretion. With increasing concentration of radio-labelled hormone the receptor binding is also found to increase linearly up to a certain concentration and then decrease. The [¹²⁵I] murrel GtH binding characteristics to a preparation of common carp ovarian plasma membrane shows saturability with high affinity. Scat chard plot analysis gave dissociation constant (Kd) of 0.81 X 10(super -9) M and maximum binding capacity (MBC) of 22.05 f mole/mg protein.

Culture suitability of two exotic catfishes (Clarias gariepinus and Pangasius hypopthalamus) with an indigenous catfish (Heteropneustes fossilis)

Culture experiment of African catfish ( Clarias gariepinus) and Thai pangas (Pangasius hypopthalamus) with indigenous stinging catfish (Heteropneustes fossilis) was conducted in the laboratory. The study was conducted for two experiments, where C. gariepinus and P. hypopthalamus were used separately with H fossilis for a duration of 2l days with three feeding treatments, viz. Tubificid worms (T1), SABINCO feed (T2), and no supplemental feed (T3). In experiment 1, the initial length and weight of 4.4cm and 0.60g of C. gariepinus became 6.74cm and 2.33g when fed Tubificid worms, 7.07cm and 2.84g when fed SABINCO feed in the treatment without supplemental feed the final length and weight were 3.67cm and 0.3lg at the end of 21 days of trial. The final length and weight of H fossilis reached 4.55cm and 0.53g from the initial 3.3cm and 0.25g under the treatment fed Tubificid worms while those fed SABINCO feed showed a length and weight of 4.37cm and 0.45g respectively. However, both the initial length and weight were reduced to 2.85cm and 0.12g respectively in the treatment without supplemental feed. In experiment 2, the initial length and weight of 4.37cm and 0.57g of P. hypopthalamus became 5.57cm and 0.57g when fed Tubificid worms, 4.85cm and 0.82g when fed SABINCO feed in the treatment without supplemental feed the final length and weight reduced to 3.95cm and 0.34g at the end of 21 days of trial. The final length and weight of H fossilis reached 5.19cm and 0.82g from the initial 3.25cm and 0.20g under treatment fed Tubificid worms while those fed SABINCO feed showed the final length and weight of 4.93cm and 0.70g respectively. And both the initial length and weight were reduced to 3.07cm and 0.04g respectively in the treatment without supplemental feed. No predatory effect of C. gariepinus and P. hypopthalamus on H fossilis was observed in the experiments.

Investigation of health status of juvenile exotic carps from various farming conditions of Bangladesh

Health status of juvenile silver carp, Hypophthalmichthys molitrix and silver barb, Barbodes gonionotus were investigated in three fish farms following different farming conditions through clinical and histopathological examinations for a period of nine months. Here the fishes and water quality parameters were sampled on monthly basis. Among the water quality parameters, water temperature has a distinct effect on fish health observed during the winter season. Different clinical signs like scale loss, dermal lesion, fin erosion were observed, while histopathologically necrosis, pyknosis, inflammation, haemorrhage, hypertrophy, vacuoles, missing of gill lamellae and clubbing were evidenced in the investigated fishes. The study showed that pathological symptoms were mainly increased during the winter season and H. molitrix exhibited severe pathological symptoms in compare to B. gonionotus during the investigation. It was also found that fishes of BAU farm was comparatively in the best condition, while, the fishes of other farms were severely affected during the experimental observations. In addition, disease like Epizootic Ulcerative Syndrome (EUS), protozoan disease and suspected bacterial colonies were clearly evidenced in the fishes of Government and NGO fish farms.

Impact of common carp, Cyprinus carpio (L.) and Nile tilapia, Oreochromis niloticus (L.) on arthropods population, zoobenthos and weeds in rice-fish culture

An experiment was carried out in the fields of the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh, Bangladesh to determine the impact of common carp (Cyprinus carpio) and tilapia (Oreochromis niloticus) culture on arthropod population, zoobenthos and weeds of rice field. The treatments were: (1) rice combined with mono sex tilapia, (2) rice combined with common carp, (3) rice combined with a mixed culture of mono sex tilapia and common carp and (4) rice alone. It was observed that tilapia significantly reduced the number of arthropods, green leafhoppers and white leafhoppers in the rice-fish production systems. Benthos analysis revealed significant effects of fish culture on the abundance of molluscs, oligochaete worms and chironomid larvae. Lowest number of benthos was obtained in the treatments with common carp and significant reduction of the weed biomass was observed, especially in the tilapia containing plots. Based on the results of the study it can be suggested that common carp may play an important role in controlling of benthic organisms, while tilapia might be more effective to control terrestrial arthropods and weeds.

Studies on the growth and production of six major and exotic carps in Nasti baor, Jhenaidah, Bangladesh

An investigation on growth, production and fishery of three Indian major carps: rohu, Labeo rohita, catla, Catla catla and mrigal, Cirrhinus mrigala and three exotic carps: silver carp, Hypophthalmichthys molitrix, grass carp, Ctenopharyngodon idella, and common carp, Cyprinus carpio was carried out in Nasti baor during February to April months. In catch per unit effort (CPUE) study the highest catch/day/person (3.13 kg) and catch/day/gear (40.65 kg) was recorded in the month of March for kochal fishing. In komar fishing catch/day/person (15.08 kg) and catch/day/gear (1206 kg) was also found higher in March. Komar fishing was done only in March and April and its CPUE was greater in both the months than that of kochal. The average recovery rate (combination of all six species) was 37.80 considering the stocking from July month of the previous year. The recovery rate of common carp (54.1) was the highest and lowest (13.90) in case of silver carp. When the recovery was calculated on the basis of one year data and stocking, it was 55.6%. Analysis of production model revealed that the present production (54,806 kg/year) is less than both theoretical production (model I- 85,285 kg/year and model II -75,952 kg/year) estimated. Therefore, it may be concluded that the fish production from Nasti baor could still be increased from the present level of production.