Copepods are important organisms in the food chain of aquatic environments, and their excretion acts as a natural substrate for bacterial production. These excretions create a nutrient- and carbon-enriched microhabitat that encourages bacterial growth. In a Biofloc Technology (BFT) system, the addition of copepods can be an advantageous strategy, as their abundance and bacterial productivity can mean improved water quality and better zootechnical performance; added to the fact that copepods can be a suitable nutrient source for cultivated shrimp. The aim of this study was to evaluate the influence of the addition of copepod Apocyclops panamensis on the culture of Litopenaeus vannamei reared in a BFT system.
A 60 day-trial was conducted at the VSAREC in Hampton, VA. After nursery, Pacific white shrimp (0.056±0.003) juveniles were stocked at 500/m3 in nine, 300 L circular tanks. Three treatments (three replicates) were tested: T1 – Clear water and copepod addition; T2 - BFT and copepod addition and; T3 – BFT without copepod addition. The copepod density was keep at 5000 / L (the number of copepods in tanks were checked once a week). Shrimp were fed with a commercial diet (provide by Zeigler Bros., Gardners, PA). Weekly rations were adjusted based on shrimp consumption and growth performance. Tanks were maintained with no water exchange through the duration of the study except for CW treatment where 100% of water was change 3 times per week. Water temperature, salinity, dissolved oxygen (DO) and pH was recorded twice daily (0800 and 1600. Water was tested daily for measuring TA-N. Monitoring of NO2-N, and NO3-N was done every three days, while alkalinity was measured once a week. Total suspended solids (TSS) and settleable solids (SS) were measured once a week. Every week, 30 shrimps were randomly sampled from each tank and individually weighed. At the end of the trial, total shrimp biomass along with individual weights of the total of survival from each tank were recorded. Water quality parameters were compared by two-way repeated measures ANOVA (system type). Significant differences of P<0.05 was used in all zootechnical performance, Tukey’s multiple-range test was applied when significant differences were detected.
The presence of copepod provided better fixation of nitrifying bacteria resulting in a better stabilization of nitrogen compounds in treatments with copepod addition (Figure 1). In the zootechnical performance there was no difference between treatments, even in clear water (Table 1).
Figure 2. Mean values of nitrite (mg L-¹)