ABSTRACT. The aim of this paper was evaluate the performance of Nile tilapia fingerlings (Oreochromis niloticus) raised at hyper intensive stocking density in a recirculating aquaculture system (RAS) with minimum water replacing. The experimental system was performed in a single-batch nursery system to obtain 50 g fish size in 60 days. Fish (2.07 ± 0.04 g) were stocked in triplicate at 400 (T1), 500 (T2) and 600 (T3) ) was significantly higher than T3 (0.83 g day -1 ; 4.80% day -1 ). The specific growth rate (SGR) of T1 was 41% influenced by temperature. For T2 and T3 the SGR were influenced by the variation of dissolved oxygen (DO) that explained 47 and 44% of the fish weight variation, respectively. The SGR from T3 was also affected by the concentration of ammonia nitrogen (31%). The high stocking density affected the overall size of fish and the size homogeneity, but had no negative effect on the length-weight relationship (L-W). Data support the conclusion that fingerling stocked at 400 and 500 fish m -3 shows high performance during 9-weeks when the biomass not exceed 37 kg m -3 . At this time fish have reached the desired final nursery weight (50 g) for transfer to grow-out facilities. Keywords: Nile tilapia, recirculating aquaculture system, low water exchange, intensification. Rendimiento de juveniles de tilapia del NiloOreochromis niloticus en un sistema híperintensivo de recirculación acuícola con mínimo recambio de agua RESUMEN. El objetivo de este trabajo fue evaluar el rendimiento de juveniles de tilapia del Nilo Oreochromis niloticus sembrados en densidades hiperintensivas en un sistema de recirculación acuícola (SRA) con mínimo remplazo de agua. El sistema experimental consistió en un sistema de precría de cosecha única para obtener peces de 50 g en 60 días. Los peces (2,07 ± 0,14 g) se sembraron por triplicado a densidades de 400 (T1), 500 (T2) y 600 (T3) peces m -3 (0,84; 1,05; 1,22 kg m -3 ). El SRA funcionó con 12.000 L de agua recirculante y un remplazo diario de 252 L (2,1% por día). La densidad de siembra no afectó significativamente la supervivencia (89,5-93,6%). El biofiltro removió el amonio nitrogenado total con una eficiencia del 46,9 ± 7,0%. La tasa de crecimiento de T1 (0,96 g día -1 ; 5,01% día ; 4,80% día -1 ). La temperatura influyó 41% en la tasa de crecimiento específico (TCE) de T1. La concentración de oxígeno disuelto (DO) influyó en la variación de peso en T2 (47%) y T3 (44%). La TCE de T3 también se vio afectada por la concentración de nitrógeno amoniacal (31%). El aumento de la densidad de siembra afectó el tamaño y la homogeneidad de tallas de los peces, pero no afectó la relación longitud-peso (L-P). Los datos respaldan la conclusión que los juveniles sembrados a densidades de 400 y 500 peces m -3 tienen alto rendimiento durante nueve semanas consecutivas, siempre y cuando la biomasa no se exceda de 37 kg m -3 . En este tiempo los peces alcanzan el peso final esperado de precría (50 g) y pueden ser transferidos hacia las instalaciones de engorde. Palabras clave: tilapia ...
The protozoan Perkinsus marinus is considered the most important pathogen of the eastern oyster Crassostrea virginica, causing high mortality in natural and farmed oysters on the Atlantic coast of the US. In Mexico, no serious P. marinus epizootic has been reported. This study describes the current state of P. marinus prevalence in Terminos Lagoon (Mexico) associated with environmental factors including salinity, temperature, ammonium, nitrate, nitrite, silica, and phosphorus. In addition, the association of physiological (hemocyte density, protein concentration) and immunological (lysozyme, agglutination) parameters with the infection were studied. The prevalence was significantly different among seasons with mean values of 70, 23, and 7% in the dry (February to May), rainy (June to September) and north-wind (October to January) seasons, respectively. Only light infection intensity (Mackin scale value <1) was observed. Prevalence of P. marinus was associated with seasonal salinity, phosphorus, and silica variations. Comparisons of oyster health demonstrates that the rainy and north-wind seasons are stressful periods. Redundancy analysis showed that only 34% of the variation in seasonal P. marinus prevalence was explained by protein concentration (21%), lysozyme (12%), and agglutination (1%). Overall, the data suggest that freshwater input associated with high nutrient concentrations during the rainy and north-wind seasons has a strong negative effect on P. marinus prevalence and also influences the oysters' physiology. It is probable that this seasonal stress was responsible for the absence of an epizootic event in Terminos Lagoon. KEY WORDS: Perkinsus marinus · Crassostrea virginica · Environmental control · Salinity · Silica · ProteinResale or republication not permitted without written consent of the publisher
A critical problem in the production of Nile tilapia Oreochromis niloticus in intensive and hyper-intensive systems is the heterogeneity of body sizes as it influences the final production and economic yield. The objective of this study was to calculate the bioeconomic effect of size heterogeneity on the production of Nile tilapia at a commercial level and to determine the optimum harvest time (OHT) considering four minimum marketable sizes target (Mms = 350, 400, 450, 500 g). Two seeding strategies were evaluated: homogeneous seeding (HM) with a 96.55 ± 24.51 g initial body weight and heterogeneous seeding (HT) with a 100.17 ± 5.91 g initial weight. Fish from both treatments were stocked at 40 fish m-3 in triplicate using a randomized design. The calculated quasi-profits of variable costs showed an inversely proportional relationship with the minimum market size in both groups. The smaller size dispersion in HM generated higher profits than HT. The OHT for Mms [350, 500 g] of HM population was 180 days, with a mode of 641 g. The OHT was also 180 days for the HT population but only for the Mms [350, 400 g] and a mode of 578 g. In terms of quasi-profits, the HM produced 19.93% more quasi-profit than the HT in the market size of 350 g at 180 days (HM = 0.50 US$ kg-1; HT = 0.44 US$ kg-1). The simple bioeconomic model presented here can help producers manage a series of economic decisions associated with OHT, when targeting different market segments requiring different Mms.
The effect of long-term freshwater acclimation on the blood and plasma ion composition of Red Drum Sciaenops ocellatus was investigated with the goal of elucidating the necessity of ion remediation. Four replicates (n = 50) of freshwater-acclimated (FW) fish (1.6 ± 0.2 g) were raised in 25-m(3) tanks supported by 140,000 L of recirculating water. Four replicates (n = 50) of seawater (SW) fish groups were placed in 40-m(3) offshore cages at 32-35 psu. Blood was collected from 100 fish (FW = 578 ± 50 g; SW = 686 ± 45 g) of each group (FW, SW) after 8 months of rearing. During the grow-out phase, the survival of FW and SW fish was 57.5% and 92.2%, respectively. The water ion composition (mainly the Ca(2+)/K(+) [43%] and Ca(2+)/Mg(2+) ratios [1%]) explained 56.6% of the plasmatic ion variability in the fish groups. Freshwater exposure produced significant reductions in osmolality and in several plasma indicators (Na(+), Cl(-), and Mg(2+)); the K(+) levels from FW fish were the most compromised parameter. The water Ca(2+)/Na(+) ratio had a greater influence (44%) on the plasma chemistry parameters, mainly glucose and creatinine. Freshwater-acclimated fish had a higher percentage of hematocrit, hemoglobin, and red blood cells than SW fish, but the water quality explained only 12.5% of the blood parameter variability between the FW and SW groups. The results support the conclusion that Red Drum tolerates salinity variations and can adopt a relatively stable condition for short periods; however, the data suggest that Red Drum have only a limited ability to withstand a hyposmotic environment for long periods due to their limited ability in maintaining K(+) concentrations without external supplementation. Freshwater environments with high Ca(2+)/Na(+), Ca(2+)/K(+), and Ca(2+)/Mg(2+) ratios appear to be a chronic stress factor that should be considered in future experiments.
There are no precedents concerning the quality of Octopus maya during chilled storage. This study evaluated the shelf life of the red octopus in chilling storage (4 o C) and the correlation of the sensory quality index with microbiological counting and the biochemical indicators (hypoxanthine, histamine and volatile amines). A total of 112 whole raw octopuses (average weight of 896 g) were randomly selected from seven batches and exposed to 4°C for 18, 24, 48, 72, 84, 96, and 100 h. The histamine concentration (91.7%), followed by the counts of psychrotrophic bacteria (5.5%) and hypoxanthine (2.2%), were the predictors from the redundancy analysis that better explained the changes taking place during the chilling hours. After 72 h of chilling, the microbial count was determined to be log 4.7 CFU/g, and the octopus samples were classified as B quality (minor sensory quality defects) based on the sensory quality scale. Although the samples were not classified as unacceptable at 100 h of refrigeration by the sensory index, the level of histamine reached the defect action level (5 mg/100 g) as ruled by the International Food Safety Authorities. The shelf life of the red octopus in chilling storage was predicted to be 119 h.
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