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.

A 40-day feeding experiment was conducted to investigate the effect of previous food restriction on the compensatory growth response in Chinese shrimp, Fenneropenaeus chinensis. Four groups of shrimp with initial body weight of 2.189±0.093g (mean±SE) were used, in which the contro group (Group C) received ad libitum rations throughout the experiment, and the other three groups (expressed as Group R4, R8, and R12) were first fed at 4%, 8% and 12% of body weight per day (% B.W.•day-1), espectively, for 10 days and were then fed ad libitum for a recovery period of 30 days. After 10 days of estricted feeding, the shrimp showed increased body contents of moisture and ash and decreased contents of lipid, protein, and energy compared with the controls. The effect of previous food restriction on body biochemical composition gradually reversed during the period of ad libitum feeding. At last, there were no significant differences in body composition among all groups, with the exception of a higher lipid content appeared in Group R12. Specific growth rates in terms of wet weight, dry matter, protein, and energy (SGRw, SGRd, SGRp, and SGRe) decreased with decline in ration, while feed conversion efficiencies (FCEw, FCEd, and FCEp) were highest at feeding level of 12% B.W.•day-1 during the course of food restriction. Following transfer from restricted to ad libitum feeding regime, all the restricted groups exhibited significantly higher food intake (FIw) and SGRw than the control group. However, this compensation response only occurred within the first 10 days of ad libitum refeeding. During the period of ad libitum refeeding, all the restricted groups showed just slightly higher feed conversion efficiencies than that of the control group. At the end of the experiment, Group R12 was able to fully catch up with the control in body weight, while the other two restricted groups still weighed less than the control. It appears that both completely and partially compensatory growth occur in Chinese shrimp, and this growth compensation is mainly dependent on increasing food intake (hyperphagia) and possibly is contributed somewhat by improvement in feed conversion efficiency.

The effects of protein restriction in the diet with subsequent realimentation on growth responses of juvenile Chinese shrimp, Fenneropenaeus chinensis (initial mean wet weight 1.347 g), were investigated. The control group (Group C) was fed an adequate diet containing 44.6% crude protein and 18.5 kJ gross energy/g dry matter throughout the experiment. For treatment Groups T15 and T30, in the restriction phase (weeks 1-2) dietary crude protein contents were reduced to 15.0% and 29.3%, respectively, with constant energy supply, while in the realimentation phase (weeks 3-6) they were supplied with the same diet as the control group. Protein restriction led to significant decrease in specific growth rates and body weight of shrimp. However, when the shrimp were transferred from protein restriction to realimentation, they had significantly increased specific growth rates in terms of dry matter, protein and energy (SGRd, SGRp and SGRe) compared with the control shrimp. At the end of the experiment, the shrimp in Group T30 achieved complete growth compensation, while those in Group T15 were still significantly smaller than the controls. As dietary protein levels reduced, feed conversion efficiencies and apparent protein digestibility decreased, but feed intake and protein efficiency ratio increased. The shrimp responded to a change from protein restriction to realimentation by displaying improved feed conversion efficiencies (FCEd, FCEp and FCEe) compared with the controls, although those in Group T15 delayed in showing the enhanced FCE values. In the initial 2-week realimentation, the shrimp in Group T15 showed significantly higher feed intake, and lower apparent digestibility of dry matter and protein than those of the controls. There was no significant difference in protein efficiency ratio among all groups in the realimentation phase. The above results suggest that compensatory growth in Group T30 is mainly dependent on improved feed conversion efficiencies, while that in Group T15 is attributable to both improved feed conversion efficiencies and increasing feed intake. After 2-week restriction, the shrimp showed lower body crude protein, lipid and energy content, and higher moisture and ash content than the controls. However, during the course of realimentation, the differences between the previously protein restricted shrimp and the controls diminished. This indicates that compensatory growth after a period of protein restriction in juvenile Chinese shrimp was accompanied by a complete recovery in body composition and energy content.

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.

The specific growth rate (SGR) over 45 days of Fenneropenaeus chinensis shrimp with initial body weight of 1.979F0.036 g under different light color was as follows: natural>green>yellow>blue light. The SGR of shrimp under blue light was only 73.0% and 85.8% of those under natural light and green light, respectively. The maximal and minimal feed intake (FI) of the animal occurred under blue light and yellow light (difference 16.6%), respectively. The lowest food conversion efficiency (FCE) occurred in the blue light group (64.5% and 75.8% of that under natural and green light, respectively). FCE values between blue and natural light groups were significantly different (P<0.05). F. chinensis was relatively sensitive to blue light, under which the animal was active in feeding behavior, and gained a higher FI as well as a lower FCE, and therefore, a lower SGR.Shrimp may grow faster in the organically rich earthen ponds than in organically poor waters because there is less blue light spectrum in earthen ponds.

The specific growth rate (SGRd) of juvenile Fenneropenaeus chinensis shrimp was measured over 35 days under different light intensities: 0, 50, 300, 1300 and 5500 lx. The SGRd of the shrimp under 5500 lx was only 29.4%, 27.1%, 21.1% and 19.7% of those under 0, 1300, 50 and 300lx, respectively ( P<0.05). The maximal and minimal feed intake (FId) of shrimp occurred under 300 and 5500lx, respectively (difference 9.3%). The lowest food conversion efficiency (FCEd) occurred in the 5500 lx group (30.2%, 26.3%, 21.3% and 21.1% of those under 0 lx, 1300lx, 50lx and 300lx, respectively). FCEd values between 5500 lx and other groups were significantly different (P<0.05). The shrimp under 5500 lx gained a lower FI as well as a lowest FCE and therefore exhibited a lower SGR. The results revealed that light intensity affected the growth of the shrimp mainly by influencing FCE, or energy allocation to growth. Therefore, the shrimp may grow better in organically rich earthen ponds that have lower light intensity.

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.

The effects of temperature changes on oxygen consumption of Chinese shrimp (Fenneropenaeus chinensis Osbeck) were studied. The response of oxygen consumption to a temperature rise was conformed to partial metabolic compensation. No compensatory response was observed at lower temperature. A sudden temperature increase by 12℃ resulted an overshoot in oxygen consumption in shrimp adapted to 19℃, while a sudden decrease by 12℃ in shrimp adapted to 19℃ resulted in an undershoot in oxygen consumption. The shrimp adapted to 31℃ responded with an undershoot in oxygen consumption when a sudden temperature drop by 12℃ occurred. But overshoot in oxygen consumption did not occur when the shrimps were transferred back from 19 to 31℃. The amplitude of oxygen consumption was reduced in shrimp during the process of acclimation to the temperature diel fluctuation. After the shrimp had adapted to the temperature fluctuation, the daily mean oxygen consumption of shrimp at diel temperature fluctuation from 24 to 30℃ was significantly lower than those adapted to the constant temperature at 27℃ (P<0.05). The decrease in metabolic rate may account for the increase in the growth rate of shrimp at a diel fluctuating thermal regime. D 2004 Elsevier B.V. All rights reserved.