The effects of seawater Na/K ratio on growth and energy budget of juvenile Litopenaeus vannamei Boone, 1931 were investigated. Salinity (S=0ppt) and the total concentration of sodium and potassium in the experimental water were kept constant. Seven treatments were set: R1, R2, R3c, R4, R5, R6 and R7, the Na/K ratios were 25.6, 34.1, 47.3, 85.2, 119.3, 153.3 and 187.4 (mmol/mmol), respectively. The shrimp in R7 (Na/K=187.4) died within 2 weeks after the experiment began. After the 30-day feeding trial, the molting frequency (MF) and feed intake in terms of wet weight (FIw) and energy content (FIe) of the shrimp under the other six treatments were not significantly affected by the different Na/K ratios in the seawater. The final wet weight, weight gain (WG), specific growth rates (SGRw and SGRe) and food conversion efficiencies (FCEd and FCEe) of the shrimp under Treatment R6 were significantly lower than those under the other five treatments. There was a trend that, with all the indices mentioned above, the values of the test shrimp under Treatment R2 was the highest, and the sequence was: R2 (Na/K=34.1)>R3c (Na/K=47.3)>R1 (Na/K=25.6)>R4 (Na/K=85.2)>R5 (Na/K=119.3)>R6 (Na/K=153.3). In the experiment, the percentages of energy deposited for growth (G), energy lost for respiration (R), energy lost in excretion (U) and energy lost in exuviae (E) to the energy consumed in food (C) were significantly affected by the different Na/K ratios in seawater, while the percentage of energy lost in feces (F) to C was not significantly affected by the ratios. The percentage of G to C of the test shrimp under Treatment R6 was significantly lower while the percentage of E to C was significantly higher than those under the other treatments. There were no significant differences among the energy allocations of the test shrimp under Treatment R1, R2, R3c, R4 and R5. According to regression analysis, optimal shrimp growth could be obtained by regulating the Na/K ratio of the seawater to 40-43 at a salinity of 30 ppt.

Study of the feeding capacity of silver carp and bighead carp by means of experimental ecology showed that the fultering frequcecy of silver carp was slightly greatce than that of bighead carp. But that the latter’s suction volume was much greater than the former’s so the filtering rate (filtering frequency mul-tiplied by the suction volume) of silver carp was smaller than that of bighead carp. The removal rates of silver carp for phytoplankton were greater than those of bighead carp, hut of zooplankton the former were smaller than the latter. For food particles about 70um both removal rates were almost equal. The feedingling habits of the two species in natural waters is also dicussed in the paper.

Allelopathic effects of fresh tissue and dry powder of a nonsexual and a sexual strain of the macroalga Ulva pertusa on the growth of the microalgae Heterosigma akashiwo and Alexandium tamarense were evaluated using long-term coexistence culture systems in which several concentrations of macroalga fresh tissue and dry powder were used. The effects of macroalga culture medium filtrate on the two HAB algae were also investigated. Moreover, isolation co-culture systems were built to confirm the existence of allelochemicals and preclude the growth inhibition by direct contact. Short-term algicidal effect assays of macroalgae on H. akashiwo were carried out to measure the rate of algal cell lysis. The results of the coexistence assays showed that the growth of H. akashiwo and A. tamarense was strongly inhibited by fresh tissue and by dry powder of both strains of U. pertusa. The allelochemicals were lethal to H. akashiwo at relatively higher concentrations. The macroalga culture medium filtrate exhibited no apparent growth inhibitory effect on the two HAB algae under initial or semicontinuous filtrate addition, which suggested that continuous release of small quantities of rapidly degradable allelochemicals from the fresh tissue of both strains of U. pertusa was essential to effectively inhibit the growth of H. akashiwo and A. tamarense.