Proposal of a production and management index (PMI) for tilapia farms.

Tilapia is one of the most important species in aquaculture; however, there is no available index to show the performance of a production unit. It is desirable to assess the productivity using indexes, such as the production and management index for shrimps and the European production efficacy factor for broilers. These indexes are based on data production: growth, survival, and feed conversion of a full production cycle. Taking into account these parameters, we propose a production and management index (PMI) for tilapia that is applicable for a specific period of the production cycle. For the construction and validation of the PMI we have used production data from 8,614 monthly records of 2 tilapia farms in Huila Department (Colombia), and because of the complexity of tilapia management, different anomalous situations have been detected and then defined as exceptions. As a result, 419 records were considered extreme values because 1 or more exceptions were met. The value of the PMI varies from 0 (the worst situation) to 3.55, which reflects high variability. We have constructed a PMI for tilapia as the product of 3 elements to obtain a positive value index. Instead of classic parameters, we had to calculate an adapted version of them: the relative average daily growth, the survival (as a complementary value of the estimated monthly mortality), and a feed conversion ratio index. To assess the utility of the PMI, some comparisons were performed using records from black and red tilapia. We observed significant differences depending on tilapia strain (PMI = 1.0248 vs. PMI = 1.1661; < 0.001), age (better values for small fish), and season (PMI = 1.0847 vs. PMI = 1.1011; = 0.026). According to these results, we can conclude that the PMI could be a useful tool for tilapia farmers, despite the complexity of the calculation.

Persistence of sucrose fermenting and nonfermenting vibrios in tissues of Manila clam species, Ruditapes philippinarum, depurated in seawater at two different temperatures.

Effective post-harvest treatment to eliminate toxigenic vibrios is an important measure to reduce risk associated with seafood consumption. In the present study, we examined whether natural populations of sucrose nonfermenting (SNFV) and sucrose fermenting vibrios (SFV) persisted in Ruditapes philippinarum, after depuration at two different temperatures. Two experiments (one in Spring and one in Summer) were performed. Clams were depurated in duplicate tanks in an open-circuit seawater system using filtration and ultraviolet treatment. Clams were sampled daily (9 days), individually processed and inoculated on thiosulphate-citrate-bile salts-sucrose (TCBS) agar plates to estimate the density of SNFV and SFV. Results showed that depuration was less effective in Summer than in Spring, for SNFV and SFV. Despite an initial lower presence in the Summer experiment, clearance of SNFV was less efficient than in Spring, with 22.2% of clams presenting SNFV on day 8 and without significant changes on day 9. When compared, daily proportion of presence of SNFV and SFV in Spring, it was observed that SFV were more frequent than SNFV on days 8 and 9. In Summer these differences were significant on days 7-9. Present study demonstrated that SNFV (involved in food poisoning) are purged, at any temperature, faster than SFV.

Identification and characterization of lactic acid bacteria isolated from rainbow trout, Oncorhynchus mykiss (Walbaum), with inhibitory activity against Lactococcus garvieae.

A study was conducted to evaluate the probiotic properties of endogenous rainbow trout microbiota against pathogenic Lactococcus garvieae. A total of 335 bacterial strains were isolated from rainbow trout and screened for antagonistic activity against L. garvieae using an agar spot assay. Antagonistic strains were grouped by PCR amplification of repetitive bacterial DNA elements (rep-PCR) and identified by 16S rRNA gene sequence analysis. The results revealed that the antagonistic strains belonged to the genera Lactobacillus, Lactococcus and Leuconostoc. Further probiotic characteristics, such as specific growth rate, doubling time, resistance to biological barriers, antibiotic resistance, hydrophobicity and production of antimicrobial substances, were also studied. These strains were able to survive low pH and high bile concentrations, showed good adherence characteristics and a broad spectrum of antibiotic resistance. The antagonistic efficacy was maintained after sterile filtration and was sensitive to proteinase K, indicating that proteinaceous extracellular inhibitory compounds were at least partially responsible for pathogen antagonism. Based on these results, these strains should be further studied to explore their probiotic effects in challenge experiments in vivo. This study shows clear evidence that the indigenous trout-associated microbiota may provide a defensive barrier against L. garvieae.

Experimental uptake and retention of pathogenic and nonpathogenic Vibrio parahaemolyticus in two species of clams: Ruditapes decussatus and Ruditapes philippinarum.

AIMS: To describe uptake and retention of pathogenic and nonpathogenic Vibrio parahaemolyticus in Ruditapes decussatus and Ruditapes philippinarum. METHODS AND RESULTS: Ruditapes decussatus accumulated greater concentrations of pathogenic and nonpathogenic V. parahaemolyticus than R. philippinarum. These concentrations decreased earlier in R. decussatus. Nonpathogenic V. parahaemolyticus reached higher concentrations (approx. 1 log CFU g⁻¹ in tissues of R. decussatus and more than 1 log CFU g⁻¹ in R. philippinarum) than pathogenic V. parahaemolyticus at similar times. It also persisted longer in both species of clams (72 h in R. decussatus and 96 h in R. philippinarum), while pathogenic V. parahaemolyticus persisted 48 h in R. decussatus and 72 h in R. philippinarum. CONCLUSIONS: Ruditapes decussatus incorporated both isolates of V. parahaemolyticus faster than R. philippinarum and it eliminated both isolates earlier than R. philippinarum. Under same conditions, nonpathogenic V. parahaemolyticus might survive better than pathogenic V. parahaemolyticus within both species of clam. SIGNIFICANCE AND IMPACT OF THE STUDY: Pathogenic V. parahaemolyticus is an important cause of foodborne illnesses. This study shows it may be possible to use nonpathogenic V. parahaemolyticus to perform experimentation to evaluate bacterial evolution in clams, developing an in vivo model useful for risk analysis.

Host-microbiota interactions within the fish intestinal ecosystem.

Teleost fish are in direct contact with the aquatic environment, and are therefore in continual contact with a complex and dynamic microbiota, some of which may have implications for health. Mucosal surfaces represent the main sites in which environmental antigens and intestinal microbiota interact with the host. Thus, the gut-associated lymphoid tissues (GALT) must develop mechanisms to discriminate between pathogenic and commensal microorganisms. Colonization of intestinal mucosal surfaces with a normal microbiota has a positive effect on immune regulatory functions of the gut, and disturbance in these immune regulatory functions by an imbalanced microbiota may contribute to the development of diseases. Significant attention has therefore been recently focused on the role of probiotics in the induction or restoration of a disturbed microbiota to its normal beneficial composition. Given this, this article explores the fascinating relationship between the fish immune system and the bacteria that are present in its intestinal microbiota, focusing on the bacterial effect on the development of certain immune responses.

Effect of fish farming on the water quality of rivers in northeast Spain.

The effects of fish farming activities on the aquatic environment were evaluated by studying the water quality of twelve rivers located in northeast Spain. Two sampling sites were used for each river: the first sampling point was located just upstream from the fish farming facilities and the second one was downstream from fish farm effluent discharge point. In order to avoid any misinterpretation due to watershed location and seasonality, a stratified statistical analysis was performed. The results show significant decreases in pH and dissolved oxygen, in contrast to chemical oxygen demand, ammonia, phosphates and microbiological parameters, which significantly increased downstream from the fish farm discharges. Other significant variations were also found for conductivity and temperature. According to the European and local regulations concerning to support fish populations, our results fell within the allowable limits for salmonid waters. Nevertheless, we suggest that further investigations should be carried out to study the ecological interactions between farmed and wild fish populations.

Isolation of Vagococcus salmoninarum in rainbow trout, Oncorhynchus mykiss (Walbaum), broodstocks: characterization of the pathogen.

Coldwater 'streptococcosis', caused by Vagococcus salmoninarum, is an emerging disease of rainbow trout in the European Union, causing mortality rates up to 50% in broodstock during the spawning period, with water temperature of 10-12 degrees C. A study to determine the presence and role of this bacterium was undertaken using classical bacteriological techniques confirmed with polymerase chain reaction. This is the first report of isolation of V salmoninarum in relation to outbreaks of mortality in a rainbow trout farm devoted exclusively to broodstock rearing in Spain. A total of 10 isolates of V salmoninarum were characterized by their morphological, cultural, physiological, biochemical and enzymatic traits. Some differences were observed in parameters such as growth on MacConkey agar, H2S production, acid production from starch, and some other minor variations. Isolates were sensitive to erythromycin and oxytetracycline tested in vitro, but treatments conducted in the field were ineffective. An attempt at vaccination did not provide encouraging results.