Dong Shuanglin

Comparative studies on nitrogen budgets of closed shrimp polyculture systems

April to October, 1997 comparative studies on the nitrogen budgets of closed shrimp polyculture systems showed that, in all the studied polyculture systems, nitrogen from feeds and fertilizers were the main input items, which comprised 70.7%–83.9% of the total input nitrogen 3.2%–7.4% of which was provided by nitrogen fixation. It was in monoculture enclosures (Y-4, Y-11 and Y-12) that the percentage reached the maximum value. The output nitrogen in harvested products comprised 10.8%–24.6% of total input nitrogen, and the highest percentage, 24.6%, was found in shrimp-fish-tagelus polyculture systems. In shrimp monoculture and shrimp-fish polyculture systems, they were 19.1% and 21.9% respectively. The nitrogen utilization efficiency was different and varied from 12.2% was found in shrimp-tagelus polyculture systems. The lowest, 12.2%, was found in shrimp monoculture systems. All the nitrogen utilization efficiencies in shrimp-fish systems or shrimp-scallop systems seemed to be higher than that of the monoculture system, but they showed little statistical difference. The main outputs of nitrogen were found in sediment mud, and comprised 48.2%–60.8% of the total, input, the lowest percentage was found in shrimp-fish-tagelus polyculture systems, and the highest percentage in shrimp-scallop systems. During the experiment, nitrogen lost through denitrification and ammonia volatilization comprised 1.9%–6. 2%, averaged 2.8%, of the total input, and the loss through seepage comprised 5.9%–8.9% of the total. The estimated nitrogen attached to the enclosure wall comprised 3.7%–13.3% of the total, and was highest in shrimp monoculture systems. Compared with the classic shrimp farming industry, the closed shrimp polyculture systems may improve the nitrogen utilization efficiency, and hence reduce the environmental impacts on coastal waters. The nitrogen discharging rates for all the studied polyculture systems ranged from 3.0% to 6. 0% of total input nitrogen.

Comparative studies on the feeding capacity of silver carp and bighead carp

Study of the feeding capacity of silver carp and bighead carp by means of experimental ecology showed that the filtering frequency of silver carp was slightly greater than that of bighead carp, but that the latters suction volume was much greater than the formers so the filtering rate (filtering frequency multiplied by the suction volume) of silver carp was smaller than that of bighead carp. The filtering efficiency of silver carp for phytoplankton was greater than that of bighead carp for them. The removal rates of silver carp for phytoplankton were greater than those of bighead carp, but for zooplankton the former were smaller than the latter. For food particles about 70 μm both removal rates were almost equal. The feeding habits of the two species in natural waters is also discussed in the paper.

Carbon cycle in shrimp polyculture mesocosm

The carbon cycle in shrimp polyculture mesocosm ecosystems was studied in the shrimp farm of the Huanghai Fisheries Group Corporation in Shandong Province from May to August, 1997. The results showed that the plankton community respiration rate fluctuated between 0.07 and 2.28 mgC/(L·d), average of 0.82±0.42 mgC/(L·d), which was 49 percent of the rate of phytoplankton gross production; that the average respiration rates (mgC/(L·d)) of micro-, nano- and pico-plankton were 0.07, 0.38 and 0.31, which were 175, 30 and 207 percent of the corresponding sized phytoplankton production rates; that the sediment respiration rate (mgC/(m2·d)) varied from 178.64 to 373.23, average of 262.60±48.68, and increased gradually with the lapse of culture time; and that the organic carbon accumulation and the respiration in the sediment of the shrimp monoculture mesocosm was higher than that in the polyculture mesocosms. The total sediment respiration per 25 m2 mesocosm in the culture period averaged 571.16 gC, which was 10 percent of the total organic carbon input of the mesocosm.

Food sources and carbon dudget of chinese prawnPenaeus chinensis

This study deals with contribution of artificial food pellet and natural food to Chinese prawn (Penaeus orientalis) growth in a semi-intensive culture pond. The prawn carbon consumption, budget, and the effects of some factors on the budget were investigated. The results showed that 26.2% ofP. orientalis growth carbon came from formulated feed at the initial culture stage (when the prawns were 0.06±0.01 g in wet weight), and was 62.5% when the prawns were 9.56±1.04 g. The remaining part of the growth carbon was derived from organic fertilizer and natural food. The highest growth rate occurred at 20×10−3 salinity. Suitable salinity for culturing Chinese prawn was (20–28)×10−3.

Summary of studies on closed-polyculture of penaeid shrimp with fishes and moluscans

Closed-polyculture of Chinese penaeid shrimp, Taiwan red tilapia, and molluscans(constricted tagelus and bay scallop) was studied from 1995 to 1997 with the enclosure-experiment method, on a shrimp farm in Haiyang County, Shandong Province. Four structure-optimized closed-polyculture systems, i. e., the “shrimp-tagelus” system, the “shrimp-scallop” system, the “shrimp-tilapia” system and the “shrimp-tilapia-tagelus” system, were worked out. All these polyculture systems were superior to shrimp monoculture system in economic and ecological efficiencies. The order of these polyculture systems in efficiencies was “shrimptilapia-tagelus” > “shrimp-tagelus”>“shrimp-tilapia”>“shrimp-scallop”. The “shrimp-tilapia-tagelus” system raised the production by 28% and the utilization efficiency of input nitrogen by 85%. These closed-polyculture systems reduced the nitrogen discharge ratio to 6%–8%, instead of 40%–90% in the usual open culture systems. The ecological features of the systems were also investigated and many meaningful results have been obtained. The mechanism enhancing the efficiencies of these systems, the ways to enhance the efficiencies further and those to reuse the sedimented materials are disscussed.

Redescription and taxonomic reconsideration ofNemertopsis gracilis var.bullocki Coe, 1940

Specimens ofNemertopsis gracilis var.bullocki Coe, 1940 collected from Huian, Fujian Province, China, are described. The variety is upgraded to specific level on the basis of: the dorsal surface having a pair of blackish brown longitudinal stripes meeting anteriorly with a broad transverse band of the same color; the proboscis having 11–13 distinct proboscis nerves in its longitudinal muscle layer.

Effects and mechanism of ambient Mg2+ and Ca2+ concentrations on growth and energy budget of juvenile Litopenaeus vannamei.

In order to clarify the ionic regulation methodology for shrimp farming with inland saline waters,a feeding trial was conducted to investigate the effects and mechanism of ambient Mg2+ and Ca2+ concentrations on the growth and energy budget of juvenile Litopenaeus vannamei using artificial seawater at salinity 30. Eight treatments were set:R1,R2,R3,R4,R5,R6,R7 and R8,and the Mg2+/Ca2+ ratios and Mg2+,Ca2+ concentrations (mg/L) were 0.11(35,330),0.53(175,330),1.59(525,330),2.42(800,330),3.36(1110,330),4.78(1110,232),7.87(1110,141) and 11.81(1110,94),respectively. The experiment lasted 40 days,but Treatment R8 just continued for 30 days because of shrimp mortality. During the experiment,the growth,molting,food conversion efficiency and energy budget of L. vannamei were all significantly affected by both Mg2+ and Ca2+ concentrations in the water (P0.05). However,shrimp food consumption was just significantly influenced by Ca2+ concentration (P0.05),not by Mg2+. It indicated that L. vannamei had powerful ability to endure very low ambient Mg2+ concentration,but it was vulnerable to low Ca2+ concentration. In conclusion,if using Mg2+ or Ca2+ deficient saline groundwater for shrimp farming,we only need to complement the Mg2+ concentration to at least 15% of its normal level or Ca2+ concentration to 60% of its normal level in seawater by adding magnesium or calcium salt,and the shrimp growth could be normal.

ASPECTS OF IRON NUTRITION IN MACROALGAE ULVA PERTUSA (CHLOROPHYTA) UNDER IRON STRESS

Fe, Chlorophyll (Chl) and total nitrogen (TN) content in tissues were measured in Fe-deficient cultures ofUlva. pertusa over a period of 60 days. Photosynthetic carbon fixation rates were studied at the start of and 30 days after Fe-deficiency culture, when the effects of Fe-deficiency on the ultrastructure were also analyzed. The iron content in tissue decreased exponentially during Fe-deficiency (from 726.7 to 31.6 μg/gdw) and simultaneously Chl and TN content declined to 4.35% and 59.9% of their original levels respectively. Maximum carbon fixation rate (50–250 μmol/m2 s) under Fe-deficiency decreased significantly compared with the control (p<0.01) and was 13.6 to 0.365 μg C/cm2 h. Photosynthesis in Fe-deficient cells became light-saturated at lower irradiance than that in control. Ultrastructural observations of Fe-deficient cells showed reductions in chloroplast number, some degeneration of lamellar organization, an increase in vacuolar area, a decrease in mitochondrial matrix density, and variation in accumulation body number and morphology. During Fe-deficiency, the algae growth rate continued to decline and after 6 weeks of iron deficiency, no further growth was detectable. These suggested that the lower growth rate ofUlva. pertusa under Fe-deficiency could be due mainly to nitrogen utilization and inhibition of photosynthesis.