Evaluación de la sobrevivencia y calidad larval de Macrobrachium rosenbergii (De Man, 1879) en un sistema de recirculación cerrado

Abstract

The production of the giant freshwater prawn Macrobrachium rosenbergii in Peru is carried out in tropical jungle areas, with high temperatures and no access to seawater, which is why prawn producers have chosen to establish their commercial hatcheries in these areas. For which they use recirculation aquaculture systems (RAS), the brackish water for larval production is obtained by mixing fresh water with commercial sea salts or sea water, the water prepared it is used for several production cycles. The continuous use of brackish water, the concentrations of some elements necessary in the osmoregulatory and growth processes of the larvae decrease, generating a negative effect on the production of PL and their survival. Therefore, the general objective of this research has been to evaluate the larval survival of commercially produced M. rosenbergii in a hatchery in the San Martin Region in Peru, through the evaluation of the ionic quality of reconstituted brackish water in a RAS, used successively in larval production cycles. Larval production of giant river prawn M. rosenbergii and water quality in a commercial hatchery using a closed recirculation system (RAS) with artificial seawater, considering water used during 240 days (E1) and freshly prepared water (E2), was evaluated. An average of 100 larvae/L (zoea I) was stocked in four tanks of 1000 L; in both treatments, they were fed Artemia and egg custard. Survival and larval stage index (LSI) were estimated, every 5 days. Temperature, salinity and pH were monitored daily, while nitrogen compounds and ions were monitored every 5 days. Spearman and Pearson correlations were performed between larval survival and ion concentration and Mg/Ca ratio. Final larval survival differed significantly between treatments E1 (32% ± 7.5%) and E2 (50% ± 7.5%). Larval cycle lasted 23 and 21 days for E1 and E2 respectively. LSI did not differ significantly between the treatments. Water quality parameters were appropriate for the specie, although nitrate (NO3) increased to 500 mg/ L in E1 treatment. Reused water showed a depletion of magnesium (~half of it) when compared to freshly prepared water. Magnesium and potassium concentrations decreased in both treatments during E1 cycle. A positive correlation was found between larval survival and magnesium (r = 0.54) and potassium (r = 0.78) in E1, but the same was not observed in E2. Mg/Ca ratio in E1 showed an average of 1.2, whereas, in E2, the average ratio was 2.1. The depletion of magnesium and potassium ions, through the continuous use of the water in RAS, could affect the survival of larvae. A second chapter of the research was to evaluate the quality of the post larvae (PL) obtained in two commercial hatcheries with the application of stress tests. The tests used were formalin (TF) and ammonium (TA). The PL used in the tests came from the hatchery located in the San Martin Region and were produced with freshly prepared water in trial E1 and in water used in several production cycles, to which magnesium was added to compensate the loss of this ion (trial E3). Stress tests were also performed on PL from an artisanal hatchery located in Lima that uses a static system with natural seawater. This hatchery receives zoea I larvae, from the San Martin Region. Initially, the Median Lethal Concentration (LC50) was calculated for each of the compounds, the calculated LC50 concentration was used for the final stress tests. Thus, at the end of each production stage, 120 PL were exposed to formalin (600 mg/L for 1 hour) and ammonia (30 mg TAN/L for 24 hours). A survival of 60% or more was the criteria to define good PL quality. The PL from trials E1 and E2 were considered to be of good quality. However, there were significant differences between the TA (75%) and TF (48 to 57%) tests in the E3 trial, the PL were not considered of good quality. In all stress tests, the control group presented 100% survival. The PL from assay E3 underwent histological analysis of the gills, showed slight damage in the TA stress test and moderate to severe effects in the TF stress test. The stress tests applied proved to be an effective tool to detect weak or stressed PL of M. rosenbergii, depending on the larval origin or production management, its implementation and application feasibility should be evaluated and will depend on the production center.