This article explains the conference presented by Dr. Alfredo Palomino, from the Universidad Científica del Sur in Peru (UCSUR) in Biovet International Symposium in Tarragona 2018. The first session on May 28 was mostly focused on aquaculture. Under the title “Pathologies in tilapia farming”, the talk showed the general situation in the study of pathologies in the culture of tilapia and their possible treatments.

The article also exposes partial results of an experiment carried out by this university about the “nutritional evaluation of the inclusion of Alquernat Nebsui as an additive in diets for Oreochromis niloticus juvenile and fry tilapia”.Biovet’s veterinarian, Dr. Maria Soriano, has made the adaptation of the conference.

General situation of tilapia farming

Generally, the emergence of a diseases in tilapia farming are the result of a combination of different factors, the most important one is the presence and amount of the pathogen, but it is always necessary an environmental stress component, that has synergistic effect with the microorganism and allows him to beat the immune barriers of the animal.

Infectious diseases are an essential part in the existence of all organisms, but their presence is more evident and frequent in culture than in natural environment.

Even with what is mentioned before, it should be noted that most of the diseases observed in aquaculture have their origin in nutrition, water quality or contamination.

The presence of an illness, infectious or not, always conditions de normal function of cells, tissues or organs, leading to economic losses for the farmer, either by lethality, aesthetic defects or by being a zoonosis.

Initially, tilapias were labelled as “resistant to diseases”, but the intensification in production systems changed the concept, and showed that sensitivity or resistance to diseases is more related to the host than to the presence of the pathogen.

Major diseases in tilapias include the ones with nutritional origin, as well as the ones of infectious nature: viral illnesses like lymphocystis and iridoviroses, saprolegniasis and aspergillomycoses as mycotic diseases, granulomatous or not granulomatous bacterial infections, and parasitic diseases including infections by protozoa, nematodes, crustaceans and hirudinea. Almost no viral or bacterial disease are determined by a particular growth stage.

As it was mentioned in the beginning, the onset of a disease is determined by environmental factors, highlighting temperature: there are some diseases that appear between 24-28ºC, as Francisella or Streptococcus iniae, and in Flavobacterium cases, in sudden changes of temperature; others show up in higher ranges, like Streptococcus agalactiae o Streptococcus constellatus; and there are other bacterial, viral or parasitic illnesses which does not have a fixed range of temperature related to its presence.

Short term management plans, in an outbreak situation, consist of analyzing the situation and deciding if treatment is cost-effective or not, since in viral cases, there is no feasible treatment. In parasitic diseases, efficacy of the antiparasitic drugs will depend on whether arriving on time, and in bacterial illnesses, antibiotic drugs should be carefully assessed before taking a decision.

Talking about long term health management, a good preventive plan should be created to avoid the situation described above, that consists in the establishment of a proper hygiene, disinfection and biosecurity scheme, correct health and records monitoring, good management and feeding practices, setting up an appropriate vaccination program, selection of a resistant and healthy breed, and addition of pronutrients in the diet. In case of starting production in new facilities, the building site should be suitably selected and must have a good engineering design.

To conclude this review, it should be mentioned that all these factors described in the last paragraph should help farmers to reach a successful culture.

Use of Alquernat Nebsui in diets for juvenile and fry tilapias

The trial was about the nutritive evaluation of the inclusion of Alquernat Nebsui as an additive in diets for Oreochromis niloticus juvenile and fry fishes (partial results)

Alquernat Nebsui is a feed supplement that contains plant extracts with a high concentration of pronutrients, which are active biomolecules that optimize the intestinal physiology. It enhances the regeneration of the mucous membrane in the intestine, so that it improves digestion and absorption of nutrients and also prevents pathogens from damaging enterocytes.

The objective of the assay was to evaluate the effects of intestinal conditioner Alquernat Nebsui supplementation in diets for Nile tilapia (Oreochromis niloticus) juvenile and fry fishes, produced in recirculating systems, through their productive performance, chemical composition of fishes and intestinal health (histomorphology of intestinal mucosa).

The first specific objective was the evaluation of different amounts of Alquernat Nebsui in diets for tilapia fries kept in recirculating systems during a period of 12 weeks (March-June 2018). For the time being, we only have partial results relating to productive parameters, and when animals will be slaughtered, total results of the trial will be shown.

Experimental design

As 4 different treatments were performed, 16 experimental units of 40 L in recirculating system were used, with 10 fishes per unit, so there could be 4 replicates of each treatment. Experimental units were covered with a net and a black cover, with anti-stress function, and to avoid the escape of fishes and the algal boom (Pictures 1 and 2).

The flow rate was of 0.6 L/experimental unit/min, which means a 10% of dairy replacement, and the de photoperiod was of 12 hours of light y 12 hours of darkness.

Temperature, mortality, feeding and water flow were controlled daily, and monitoring of O2, ammonium, NO_2-, NO_3-   and pH value of water, twice per week.
Temperature during the experimental period ranged between 26 and 27 +/-1ºC.

Nile tilapia fry specimens (Oreochromis niloticus) arrived with a weight of 1 gr coming from La Molina National Agrarian University La Molina. 10 days adaptation to new facilities was allowed. The plant was located at UCSUR’s Faculty of Environmental Sciences .

Feeding program was provided in intervals during the day at 8, 11, 14 and 17 hours and diet waste was removed daily.

Isoproteic (36% of crude protein) and isoenergetic (4200 kcal/kg) diet was provided to the animals (Chart 3), which had included the treatment, being T1 the control and the only diet without pronutrients, and other treatments had intestinal conditioner pronutrients at different dosages: treatment nº2 (T2) had 5 gr of Alquernat Nebsui per kg of feed, treatment nº3 (T3) 10 gr/kg, and the fourth and last treatment (T4) had 15 gr/kg. Weight controls were fixed every 15 days from the beginning of the trial.

Results

As it can be seen in the chart below (Chart 4), all groups combining Alquernat Nebsui in the diet showed better growth in fresh tilapias compared to control group. T3 is the group with best results at a dosage of 10 gr/kg, being T4 the group with a higher dosage and the one that showed results similar to control group. It proved, therefore, that optimal dose of the product was exceeded.

The use of Alquernat Nebsui also allows homogenization of fish sizes amongst the trial groups, benefiting the farmer as it can be observed in the charts below (Charts 5 and 6)

Conclusion

To sum up, this trial shows that diets with 0.5% and 1.0 % of Alquernat Nebsui in fry tilapia allow them to obtain an increase of 10% in growth and a more homogeneous size at day 36 of the trial.

You can read more information at the 31st Biovet International Symposium.