Effects of different types of nutrient effluent from shrimp ponds on the seedling growth of Kandelia obovata

Extensive shrimp ponds are located next to the landward edges of most of mangrove forests in China. A shrimp pond may influence mangroves by（1） routine effluent between pond and tide, and（2） dredging effluent from pond-dredging at least once a year. Our study consisted of two experiments to study the effects of these two effluents on the seedling growth of Kandelia obovata. One experiment simulated the effects of routine effluents.The other simulated four sedimentation thicknesses（0 cm, 2 cm, 4 cm, 8 cm） over mangrove soils by dredging effluent from pond-dredging, and revealed the cumulative effects of dredging effluents on K. obovata. At each of the three fixed salinities, i.e., 5, 15 and 25, routine effluent did not result in significant differences in each of the measured growth parameters of K. obovata seedlings. However, effects of dredging effluent on seedling growth of K. obovata were related with sedimentation thickness. Most growth parameters showed maximum values at sedimentation thickness 4 cm. The data indicated that K. obovata accelerated its growth under moderate sedimentation thicknesses and it was tolerant and adaptable to shrimp pond-cleaning effluent sediments up to about 8 cm in our experiment.

GROWING NIPA PALM FOR RESTORATION OF ABANDONED SHRIMP PONDS

Rapid increase in the production of marine shrimps in the coastal zone has resulted in large-scale con-version of mangrove forests to shrimp ponds.Productions of the shrimps in some regions have been unstable.Conse-quently,a number of ponds are left idle.Restoring environmental conditions within the pond site by planting a suitablemangrove species considered an option.The experiment herein was carried out to explore the effect of planting methodson growth of Nipa palm in abandoned shrimp ponds in the Southern Thailand.Economically,coastal villagers in this areaearn their income from the palm in several ways,the most importantly in Nipa sugar production.Most seedlings wereplanted on top of furrows were constructed in the pond to avoid flooding,except for some seedlings which were planted inthe pond base where additional pond sludge were slightly filled up to compare their growth rates.The results showed thatplanting seedlings with attached rhizomes had the best growth rate and without seedling death at 14 months after plant-ing.At this stage,however,the height of seedlings grown from the fallen fruits was similar to those growth from barerooted seedlings(70 cm tall).Also,seedling mortality was not observed when growth from fallen fruits whereas about6% mortality was experienced by the bare rooted ones.Among the bare rooted seedling treatments,however no signifi-cant differences in growth rates were found when applying the soil with chemical fertilizers or farm manure or liming withCaCO3.In addition,it was found that seedling growth measured at 40 months after planting for those growths in pondbase was almost100% greater than those grown on the furrows.Therefore,this finding may be applied for the restorationof abandoned shrimp ponds by growing Nipa palm.

Heterosis and heritability estimates for the survival of the Pacific white shrimp(Litopenaeus vannamei) under the commercial scale ponds

The aim of the present study is to detect the potential of the base population from diallel crosses of eight introduced strains of the Pacific white shrimp（Litopenaeus vannamei） for improving the yield. Heterosis and heritability were estimated for pond survival at commercial farm conditions for the base population that included 207 full-sib families from a nested mating design by artificial insemination. Among all the hybrids,the heterosis ranged from –11.37%（UA1×UA2） to 20.53%（UA3×SIN） with an average of 0.953%. The results showed that more than half of the hybrids（51.85%） have negative heterosis for survival rate, but most of the hybrids with positive heterosis have high estimates. The high proportion of negative heterosis for survival rate reminders us that the survival trait also should be considered in the crossbreeding program to avoid yield decrease. However, high positive heterosis manifested in most of the hybrids for survival indicates the usefulness of these hybrids for improving the survival to obtain higher yield by crossbreeding in this breeding program. The heritability estimate for pond survival was 0.092±0.043 when genetic groups were included in the pedigree, and it was significantly different from zero（P〈0.05）. The results from this study also indicated that significant improvement for survival is possible through selection in L. vannamei.

A Study on the Contribution of Different Food Sources to Shrimp Growth in an Intensive Fenneropenaeus chinensis Pond

Stable isotope methods can be used to determine the food sources and prey items of aquatic organisms accurately and reliably. This study examined the relative contribution of artificial foods （the formulated feed and Arternia） and natural foods to shrimp growth in an intensive Fenneropenaeus chinensis pond by using carbon and nitrogen stable isotopes. The results showed that the nutrition utilization efficiency of the harvested shrimp was low, only 33.18% of feed nitrogen and 21.73% of feed carbon being converted to shrimp flesh, Our stable isotope results showed that the shrimp obtained nutrition for maximum growth from artificial foods, whose contribution was 93.5%, with the remaining attributed to the natural foods. However, there was 0.94t harvested shrimp derived from natural foods （the rest of 13.56t harvested shrimp derived from artificial foods） in lha intensive pond with a shrimp production of 14.50 tha^-1. Therefore, unit area shrimp production can be increased by increasing the contribution proportion of natural foods in intensive shrimp farming.

Differences in nitrite-oxidizing communities and kinetics in a brackish environment after enrichment at low and high nitrite concentrations

Nitrite accumulation in shrimp ponds can pose serious adverse effects to shrimp production and the environment.This study aims to develop an effective process for the enrichment of ready-to-use nitrite-oxidizing bacteria（NOB）inocula that would be appropriate for nitrite removal in brackish shrimp ponds.To achieve this objective,the effects of nitrite concentrations on NOB communities and nitrite oxidation kinetics in a brackish environment were investigated.Moving-bed biofilm sequencing batch reactors and continuous moving-bed biofilm reactors were used for the enrichment of NOB at various nitrite concentrations,using sediment from brackish shrimp ponds as seed inoculum.The results from NOB population analysis with quantitative polymerase chain reaction（q PCR）show that only Nitrospira were detected in the sediment from the shrimp ponds.After the enrichment,both Nitrospira and Nitrobacter coexisted in the reactors controlling effluent nitrite at 0.1 and 0.5 mg-NO2^--N/L.On the other hand,in the reactors controlling effluent nitrite at 3,20,and 100 mg-NO2^--N/L,Nitrobacter outcompeted Nitrospira in many orders of magnitude.The half saturation coefficients（Ks）for nitrite oxidation of the enrichments at low nitrite concentrations（0.1 and 0.5 mg-NO2^--N/L）were in the range of 0.71–0.98 mg-NO2^--N/L.In contrast,the Ksvalues of NOB enriched at high nitrite concentrations（3,20,and 100 mg-NO2^--N/L）were much higher（8.36–12.20 mg-NO2^--N/L）.The results suggest that the selection of nitrite concentrations for the enrichment of NOB inocula can significantly influence NOB populations and kinetics,which could affect the effectiveness of their applications in brackish shrimp ponds.