Invasion of Egeria into the Hawkesbury-Nepean River, Australia

The Hawkesbury-Nepean River in New South Wales (NSW), Australia, is the largest river system in the Sydney metropolitan area, and it drains most of the developing areas to the west. This catchment is under increasing pressure from urban expansion and the river frequently experiences extended periods of low flows due to a combination of extensive river regulation and the Australian temperate climate. Added to this, the river and several of its tributaries receive treated sewage and stormwater from various sources. Habitats and biota within the Hawkesbury-Nepean River catchment have been altered since European settlement and many introduced species have spread throughout the terrestrial and aquatic environment (Recher et al. 1993). Submersed macrophyte assemblages within the river have undergone significant changes in their distribution and abundance due to eutrophication, habitat alteration and changes to river flows (Recher et al 1993). Anecdotal evidence and some early unpublished studies suggest that egeria (Egeria densa Planchon), introduced from South America as an aquarium plant, was present in the Hawkesbury-Nepean River prior to 1980. Sainty (1973) reported a persistent and troublesome infestation over a number of years at Wallacia in the upper Nepean River. Here, as part of a larger study on the ecology of macrophyte and invertebrate assemblages associated with anthropogenic disturbance in the Hawkesbury-Nepean River, we document the rapid spread of egeria since 1994. Significant increases in egeria biomass were also found, and we present preliminary evidence which suggest that the native ribbonweed, vallisneria (Vallisneria americana Michx.) is being displaced.

Changes in feeding biology of Nile tilapia, Oreochromis niloticus (L.), after invasion of water hyacinth, Eichhornia crassipes (Mart.) Solms, in Lake Victoria, Kenya

Oreochrimis niloticus (L.) was introduced to Lake victoria in the 1950s. It remained relatively uncommon in catches until 1965, when the numbers began to increase dramatically. It is now the third most important commercial fish species after the Nile perch, Lates niloticus (L.) and Rastrineobola argentea (Pellegrin). Oreochromis niloticus is considered a herbivore, feeding mostly on algae and plant material. The diet now appears to be more diversified , with insects, fish, algae and plant materials all being important food items. Fish smaller than 5 cm TL have a diverse diet but there is a decline in the importance of zooplankton, the preferred food item of small fish, as fish get larger. The shift in diet could be due to changes which have occurred in the lake. Water hyacinth, Eichhornia crassipes (Mart.) Solms, which harbours numerous insects in its root balls, now has extensively coverage over the lake. The native fish species which preyed on these insects (e.g. haplochromines) have largely been eliminated and O. niloticus could be filling niches previously occupied by these cichlids and non cichlid fishes. The change in diet could also be related to food availability and abundance where the fish is feeding on the most readily available food items.

The effect of sublethal concentration of DimilinR (TH6040) on the larval development of the mud-crab Rhithropanopeus harrisii (Gould)

Sublethal DimilinR (insecticide) concentration significantly decreased the percentage survival of larval R. harrisii . This decrease was marked at low salinities, when it may have become toxic. This was true for both 25 and 30 C. Duration of larval development did not seem to be affected by sublethal DimilinR concentrations even in extremely low or high salinities. High temperature, however, shortened the time of development. No anatomical abnormality was observed. These findings are only tentative as more replicates of the experiments are needed before definite conclusions can be reached. It will be desirable to work with more salinity-temperature combinations to get a complete picture of sublethal effects under different environmental conditions.

Workers drilling on Hindburn Force in 1954

Two workers drilling on Hindburn Force, North West England, UK, making it more accesible for passing fish. This photo is part of a Photo Album that includes pictures from 1935 to 1954.

Coping with the Lionfish Invasion: can targeted removals yield beneficial effects?

Invasive species generate significant environmental and economic costs, with maintenance management constituting a major expenditure. Such costs are generated by invasive Indo-Pacific lionfish (Pterois spp.) that further threaten already stressed coral reefs in the western Atlantic Ocean and Caribbean Sea. This brief review documents rapid range expansion and potential impacts of lionfish. In addition, preliminary experimental data from targeted removals contribute to debates about maintenance management. Removals at sites off Little Cayman Island shifted the size frequency distribution of remaining lionfish toward smaller individuals whose stomachs contained less prey and fewer fish. Fewer lionfish and decreased predation on threatened grouper, herbivores and other economically and ecologically important fishes represent key steps toward protecting reefs. However, complete evaluation of success requires long-term data detailing immigration and recruitment by lionfish, compensatory growth and reproduction of lionfish, reduced direct effects on prey assemblages, and reduced indirect effects mediated by competition for food. Preventing introductions is the best way to avoid impacts from invasive species and early detection linked to rapid response ranks second. Nevertheless, results from this case study suggest that targeted removals represent a viable option for shifting direct impacts of invasive lionfish away from highly vulnerable components of ecosystems.

Nutritional properties of the invasive lionfish: A delicious and nutritious approach for controlling the invasion

Lionfish, Pterois volitans and P. miles, are native to the Indo-Pacific and have recently invaded the Western Atlantic Ocean. Strategies for control of this invasion have included limited removal programs and promotion of lionfish consumption at both local and commercial scales. We demonstrate that lionfish meat contains higher levels of healthy n-3 fatty acids than some frequently consumed native marine fish species. Mean lionfish fillet yield was 30.5% of the total body wet weight, a value that is similar to that of some grouper and porgy species. A sensory evaluation indicated that lionfish meet the acceptability threshold of most consumers.

Impact of stocking density on growth and survival rate of mud crab (Scylla serrata Froskal)

A 10-weeks culture trial of mud crab, Scylla serrata in brackish water earthen pond was conducted in different stocking densities. The aim of the experiment was to identify a suitable stocking density for optimum production. There were three treatment as 5000 crab lings/ha, 10000 crab lings/ha and 15000 crab lings/ha of each with three replications. The initial mean weight of crab lings were same (5.5 ± 0.13 g). The experimental month was June '95 to August '95. The size of each pond was 500 m². To maintain good water quality water was exchanged in every spring tide. The salinity during the experiment were 2-18ppt. Prepared feed of about 32% protein consisting fish meal, MOC rice bran and wheat flour was used at 5% of their body weight. In terms of production, survival rate, growth and carapace width, the stocking density having 10000/ha showed the best (P

Effects of cowdung application on the production of mud crab (Scylla serrata Forskal) in brackishwater pond

A culture experiment of mud crab for 84 days was conducted in earthen pond at Brackishwater Station, Bangladesh Fisheries Research Institute, Paikgacha, Khulna. The aim of the experiment was to study the effects of cowdung application on crab production and water quality. There were three treatments as without cowdung (T1), 500 kg cowdung/ha/fortnight (T2) and 750 kg cowdung/ha/fortnight (T3) with three replicates for each. The result was evaluated on the basis of growth, production, survival rate etc. The experimental months were mid-April '96 to mid-July '96. To maintain a good water quality, water was exchanged in every spring tide. The range of salinity during the experiment was 8-19 ppt. Trash fish and fresh shrimp head were used as feed on raw basis in every alternate week at a rate of 8% body weight of crab at the same time rice bran and wheat flour were used at a rate of 2% body weight as a source of carbohydrate. The production of T1, T2 and T3, were 720.35 kg, 862.16 kg and 669.19 kg/ha respectively. Though the effects of cowdung on production of crab is insignificant but in terms of production, survival rate and growth, the study suggest that the application of cowdung in addition to feed can be recommended for mud crab culture at a rate of 500 kg/ha/fortnight.

A mixed culture trail of mud crab (Scylla serrata Forskal) with tilapia ( Oreocromis niloticus L.)

A ten-month study on mixed culture of mud crab Scylla serrata with tilapia (Oreochromis niloticus) was performed in brackish water earthen ponds using live tilapia fry as the only feed for crab. The monthly growth rate varied from 9.07-19.llg among four treatments. Treatment T 1, cw: 0.68cm (±0.72) and bw: 19.11 gm (±12.97) showed highest performance which was followed by T 3, cw: 0.62cm (±0.60) and bw: 13.42 gm (±10.51), T4, cw: 0.65cm (±0.64) and bw: 13.20 gm (±9.89) and T2, cw: 0.36cm (± 0.25) and bw: 9.07 gm (±8.05). Highest survivability of crabs was also recorded in T 1 (21.5%) which was followed by T 2 (15.65%), T4 (14.95%) and T 3 (14.15%). In terms of survivability, significant differences (p<0.05) were observed among the treatments whereas these were recorded as insignificant difference (p<0.05) in final weight, weight gain and production of crabs and tilapia. Mixed culture of mud crab with tilapia could make more rewarding than crab monoculture but the study suggests that only tilapia fry can not fulfill the feed requirement of crabs in respects of survivability, final body weight and weight gain. Besides, existed salinity level of 4-12 ppt during experimental period might be the another key factor for low survivability and weight gain.

Feasibility of bi-culture of mud crab (Scylla serrata) and shrimp (Penaeus monodon)

A study on the feasibility of bi-culture of mud crab (Scylla serrata) and shrimp (Penaeus monodon) in brackishwater earthen ponds (0.1 ha each) was carried out for a period of five months (March-August). Nursed shrimp juvenile (ABL:· 3.36±0.23 em and ABW: 0.26±0.04 g) and crab juvenile (ACL: 2.61±0.22 cm, ACW: 4.63±0.11 cm and ABW: 43±2.64 g) were stocked following the experimental design of shrimp 2/m2 (Treatment-1), shrimp 2/m2 and mud crab l/m2 (Treatment-2) and shrimp 2/m2 and mud crab 0.5/m2 (Treatment-3). Crabs were fed with chopped trash tilapia @ 10~5%, while shrimp were fed with Saudi-Bangla shrimp feed @ 3~5% of biomass twice daily. Significantly (p<0.05) higher specific growth rate (SGR) of shrimp and mud crab was 1.86% (g/day) in T2 and 0.83% (g/day) in T3, respectively. The survival of shrimp and mud crab also varied significantly (p<0.05) with a higher mean value of74.63% in Tl and 51.04% in T3, respectively. The production of shrimp (424.09 kg/ha) was significantly (p<0.05) higher in Tl and that of mud crab (568.80 kg/ha) in T2. Significantly (p<0.05) highest total production of 871.29 kg!ha was in T2 followed by 708.52 kg/ha in T3 and 424.09 kg/ha in Tl. The results indicate that mud crab can be cultured at a stocking rate of 1/m2 together with shrimp at 2/m2 •

Some bacteria isolated from marine plankton and mud

57 bacterial strains isolated from marine plankton and mud from the inshore waters of Cochin, are described. The flora of the plankton was dominated by chromogens while mud sample and failed to produce chromogens. The different strains are divided into five arbitrary groups for the convenience of description. The flora is similar to that of Mandapam (east coast) while it differed from the flora of Calicut (west coast) in the paucity of Bacillus and other spore formers.