The effects of northern pike, Esox lucius, in controlling coarse fish and other pest organisms and enhancing harvest size in carp ponds was investigated. We used two treatments and one control each with three replicates. The pike density was 200 and 500 fish individuals per hectare for the first and second treatments, respectively and the control pond had no pike. The carp density in ponds was 3500 individuals per hectare and  stocking  rates  were  55% silver carp, 20% common carp, 10% bighead carp and 15% grass carp. Survival rate of the northern pike in treatments  1 and 2 was 43.8 and 40%, respectively.

The results showed that the mean (±SO) biomass of unwanted fishes (13 species) in the control treatment was 358.8±55.4kg/h and in the first and second treatments were 74.2±6.3 and 92.2±10.9kg/h, respectively in the end of the trial period. So unwanted fishes biomass reduced by 79.3% and 74.3% in the two treatments, respectively. Stomach  investigation showed that the pike fed mostly on frog juveniles and some pest fishes like Hemiculter leucisculus, Pseudorasbora parva, Carassius auratus, and few Macrobrachium and  aquatic insects. Also, the average biomass of unwanted fishes like Carassius auratus, Hemiculter leucisculus, Alburnus alburnus and Pseudorasbora parva of the first and second treatments in comparison to control showed a reduction of94, 88.9, 62.4 and 56.82 percent, respectively. A significant difference was found in the final mean weight of common carp between treatments and control ponds (P<0.05), as the weight of common carp in treatments ponds was 220% more than the control pond. Also, Esox lucius with controlling coarse fish increased cultured fish (such  as common  carp, grass carp, silver carp and  bighead  carp) production  by  about

17.9%.

Harmful algal blooms resulting in red discoloration of coastal waters in the Persian Gulf, Iran were first observed in January 2007. The species responsible for the bloom, which was identified as Cochlodinium polykrikoides, coincided with massive aquatic organisms’ mortalities in the Persian Gulf. The effects of water soluble extract (0.2, 0.6, 0.8 and 1.6 g L^-1) from 6 species of marine macroalgae; Ulva lactuca, Enthromorpha intistialis, Colpomenia sinuosa, Sargassum illicifolium, Gracilaria corticat and Hypnea valentiea , fresh thallus (2.5 and 5.0 g L^-1) and macroalgal culture medium filtrate from 3species of marine macroalgae; E.intistialis, C.sinuosa, and H.valentiea on growth of Cochlodinium polkrikoides (Dinoflagellate) were investigated for 15 days in co-culture under controlled laboratory conditions. The results clearly showed that the growth of C. polkrikoides was significantly inhibited by the water-soluble extracts of seaweed at relatively all concentrations in contrast to control with any seaweeds extract (p<0.05). The growth inhibition of C. polykrikoides was significantly higher in co-culture with fresh thallus of E.intistialis, C.sinuosa and H.valentiea (p<0.05). In macroalgal culture medium filtrate the highest growth inhibition of C. polykrikoides was obtained in co-culture with E.intistialis and was significantly higher than the other macroalgal culture medium filtrate of seaweeds(p<0.05). Therefore, we could conclude that using the tested seaweeds either as an extract or in co-culture with fresh thallus could be used as an alternative to biological control of C. polykrikoides.

In recent years the incidence of algal blooms caused by Nodularia to become one of the serious problems and is threated life of aquatic organisms in the southern Caspian Sea. Nodularia is Blue - green algae (cyanobacteria phylum) and due to production of nodularin toxin is importance. In this study, the first, three species of Pseudomonas including Pseudomonas aeruginosa, P .putida and P. fluorescens were isolated from Tajan river estuary and identified using biochemical tests and compared to standard species. The trend of Nodularia spumigena biomass (log 5) and Pseudomonas species (log 7 and 8) were examined in 30 treatments for 10 days in aquarium scale.
The results showed that the decline trend of Nodularia in P. aeruginosa and mixed species treatments were better than other treatments and log 8 of bacterium was also more inhibitory effect than to log 7. Similar results were observed in double layer on agar medium and latter treatments had algaecide effect on nodularia. However, P. putida and P. fluorescens treatments had algaestatic properties.
The conclusion showed that different strains of Pseudomonas are able to reduce the population of algae N. spumigena in aquarium scale and the results observed in combination treatment were better than other treatments.