Moderate salinities enhance growth performance of Nile tilapia (Oreochromis niloticus) fingerlings in the biofloc system

The biofloc technology (BFT) has recently gained attention as an economic and environmentally sustainable system for aquaculture. The use of BFT with salinized water could be used to minimize the negative effects of nitrogenous waste and improve the growth performance of Nile tilapia. This work evaluated the growth performance, survival, gill lesions, and fillet composition of tilapia fingerlings (Oreochromis niloticus) reared during 70 days with different salinities (0, 4, 8, 12, and 16 g/L) in a biofloc previously developed. The results indicated that the use of mature bioflocs alone was sufficient to avoid fingerling mortality due to nitrite peaks. Moreover, the salinized water, especially between 4 and 8 g/L (maximum points around 6 g/L), can be recommended in BFT to improve the growth performance of tilapia in the initial culture phase. The salinity level that was evaluated did not affect fillet composition nor the occurrence of gill lesions. The total ammonia nitrogen concentration was lower in freshwater than in salinized water (p < 0.05). Nitrite peaks in salinities of 12 and 16 g/L appeared later and were higher in comparison to other treatments. Considering minimal water exchange in BFT, the use of salinized water in this system may be environmentally viable.     

Feeding management strategies to optimize the use of suspended feed for Nile tilapia (Oreochromis niloticus) cultivated in bioflocs

Feeding strategies of tilapia (initial average weight: 32 g) cultivated with Biofloc technology (BFT) (carbon source: sugarcane, C:N ratio: 6:1) for 56 days were studied. A 4 × 3 factorial experimental design was used with four feeding frequencies (one, two, three and four times a day) and three feeding rates (50%, 75% and 100% consumption in relation to apparent satiety), with four replicates. Lower levels of dissolved oxygen, protein retention rate and body protein content were found in fish fed once a day. The reduction in feeding rate resulted in lower average final weight and reduced growth but promoted a decrease in the concentration of total ammonia nitrogen, solids, hepatosomatic index and body lipids. We found better efficiency of protein utilization at 75% feed. The nutritional value of the floc was not affected by the feeding frequency, and the feeding rate reduction from 100% to 75% did not alter the protein content of the floc. Thus, twice‐daily feeding frequency is sufficient for Nile tilapia fingerlings reared in BFT. Although the feeding rate of 100% satiety has led to better performance, it may not be the best option in BFT due to higher feed conversion and reduction of water quality.     

Depletion of florfenicol amine in tilapia (Oreochromis sp.) maintained in a recirculating aquaculture system following Aquaflor®‐medicated feed therapy

Aquaflor^® [50% w w^?1 florfenicol (FFC)], is approved for use in freshwater‐reared warmwater finfish which include tilapia Oreochromis spp. in the United States to control mortality from Streptococcus iniae. The depletion of florfenicol amine (FFA), the marker residue of FFC, was evaluated after feeding FFC‐medicated feed to deliver a nominal 20 mg FFC kg^?1 BW d^?1 dose (1.33× the label use of 15 mg FFC kg^?1 BW d^?1) to Nile tilapia O. niloticus and hybrid tilapia O. niloticus × O. aureus held in a recirculating aquaculture system (RAS) at production‐scale holding densities. Florfenicol amine concentrations were determined in fillets taken from 10 fish before dosing and from 20 fish at nine time points after dosing (from 1 to 240 h post‐dosing). Water samples were assayed for FFC before, during and after the dosing period. Parameters monitored included daily feed consumption and biofilter function (levels of ammonia, nitrite and nitrate). Mean fillet FFA concentration decreased from 13.77 μg g^?1 at 1‐h post dosing to 0.39 μg g^?1 at 240‐h post dosing. Water FFC concentration decreased from a maximum of 1400 ng mL^?1 at 1 day post‐dosing to 847 ng mL^?1 at 240 h post‐dosing. There were no adverse effects noted on fish, feed consumption or biofilter function associated with FFC‐medicated feed administration to tilapia.     

Pre‐challenge and post‐challenge haemato‐immunological changes in Oreochromis niloticus (Linnaeus, 1758) fed argan oil against Lactococcus garvieae

The present study investigated the effects of argan oil, obtained from Argania spinosa, on pre‐ and post‐challenge immuno‐haematological and biochemical responses of Nile tilapia, Oreochromis niloticus. For this purpose, the fish were fed diets containing 0, 0.5%, 1% or 2% argan oil for 45 days. Following 45 days of feeding, fish were challenged with Lactococcus garvieae and mortality was recorded for 15 days. During the pre‐challenge period, significantly higher respiratory burst activity, total white blood cell (WBC), serum lysozyme activity and myeloperoxidase activity were determined in the argan oil‐fed groups. The serum glucose and cholesterol levels decreased whilst total protein and albumin did not change in the groups fed with argan oil‐supplemented diets. After challenge with Lactococcus garvieae, the percentage survival (%) was found to be the highest in the 1% and 2% argan oil‐supplemented feeding groups. Also, there was a significant increase in weight gain, specific growth rate and feed conversion ratio in those fish fed argan oil. The results of this study indicated that after the supplementation of fish diets with argan oil, especially at 1% and 2% concentrations, the immunological, haematological and biochemical values remained similar in both the pre‐ and post‐challenge periods and the immune response against L. garvieae in Nile tilapia was modulated.     

Reproductive biology of pond reared Nile tilapia, Oreochromis niloticus L.

The reproductive performance of female Nile tilapia, Oreochromis niloticus L., reared in ponds under tropical conditions was studied. The experiments used stock matured to the age of 2–4 months and a size of 30–50 g. Oocyte development proved a better indicator for the determination of the size at first maturation than the development of the gonado-somatic index. The Nile tilapia became ‘stunted' in the sense that early breeding took place, but the somatic growth of the stock still continued. This result indicates that the earlier breeding of Nile tilapia is not a real bottleneck for the expansion of this production sector. No relationship was found between the condition factor and the size at first maturation or the relative fecundity. This led to the conclusion that aggravation of the living conditions is not a major cause of earlier breeding of pond-reared O. niloticus.     

Use of biofloc technology during the pre‐maturation period of Litopenaeus vannamei males: effect of feeds with different protein levels on the spermatophore and sperm quality

The objectives of this study were: (1) Compare two systems for pre‐maturation of Litopenaeus vannamei in terms of spermatophore and sperm quality, (2) Compare the effect of feeds with different protein levels on reproductive quality of males reared in a biofloc‐dominated system. Animals (36.40 ± 3.13 g) reared under biofloc technology (BFT) were used in the 30‐day experiment, which involved four treatments: one in a clear water system (CW) and other three in a BFT system. The BFT treatments were differentiated by feed: mix of fish, squid and crab (BFT+FF) composed of 68.48% dietary protein (DP); broodstock feed (BFT+BF) composed of 52.51% DP; and juvenile feed (BFT+JF) composed of 39.91% DP. Feed in the CW was also the mix of fresh food. Spermatophore and sperm quality were analyzed at the beginning and end of the experiment. Higher normal sperm rate was recorded in the CW compared with the BFT+FF. Among the BFT treatments, the BFT+FF had the lowest normal sperm rate. Thus, the use of BFT for pre‐maturation of L. vannamei allowed the reduction in dietary protein levels from 68.48% (BFT+FF) to 39.91% (BFT+JF) and the maintenance of spermatophore and sperm quality compared to the system based on high daily exchange rate.     

Reuse of water from biofloc technology for intensive culture of Nile tilapia ( Oreochromis niloticus ): effects on productive performance,organosomatic indices and body composition

During a growout period of 14 weeks, the productive performance, organosomatic indices and body composition of the Nile tilapia Oreochromis niloticus cultivated at high density reusing the water from systems with biofloc technology (BFT) were evaluated. Two treatments: tilapia cultured in biofloc (TB) and tilapia cultured in reused water biofloc (RW) were established. Mixed sex, juvenile Nile tilapia (average weight and length: 79.28 ± 14.44 g and 12.44 ± 0.70 cm) were stocked into 6 experimental units (0.2 m3) at a density of 100 fish/m3. Temperature, dissolved oxygen, total dissolved salts, pH, NH4–N, NH3–N and NO3–N were recorded daily, while NO2–N, general hardness, carbonate hardness and settleable solids were recorded weekly. The weight and length of the tilapias were recorded biweekly. Survival, productive performance, proximal composition and organosomatic indices of Nile tilapia were evaluated. The water parameters in RW treatment such as pH, total dissolved salts, NO2–N, NO3–N and carbonate hardness were significantly greater (p < 0.05), when compared to those obtained in TB treatment. Survival rate was > 98% under both treatments. The final weight (TB = 163.09 ± 42.34 g, RW = 159.23 ± 39.92 g), protein (19.1%) and lipid (2.2%) content of the tilapia were non-significantly different between treatments. In addition, no significant differences in the gonadosomatic and hepatosomatic indices were observed either between tilapia sex or between the treatments. The results suggest that the intensive cultivation of Nile tilapia in biofloc can be established using reuse water from BFT systems, without adverse effects on their survival, productive performance, proximal composition and gonadal development.     

Production of Nile tilapia Oreochromis niloticus grown in BFT using two aeration systems

Aeration systems used in BFT farming need to meet the dissolved oxygen demand from the biota present in the tank, as well as to keep the particulate matter in suspension. In BFT systems, it is common to use blowers, but the choice of an aerator with better efficiency in oxygen transfer and in electric energy consumption is indispensable. The vertical pump model (VPM) aerator is the most used in intensive tilapia production systems in southern Brazil. The objective of this research was to verify if this aerator model can support Nile tilapia farming under BFT system without producing negative impacts on the functionality neither of the biofloc nor in the production indexes. Simultaneous farming on BFT using blowers served as control. Oreochromis niloticus juveniles with an initial density of 7 kg/m³ were used. After 56 days of farming, the VPM aerator obtained significantly better results, both in water quality parameters and in production indexes, when compared to those obtained in the control treatment. The temperature was higher in the treatment of the blowers due to the lower thermal exchange between the atmospheric air and the tank water. Although the VPM caused lower temperatures, it obtained a productivity of 21.2 kg/m³, compared to 20.2 kg/m³ of the blowers. It was concluded that the use of the VPM aerator had no negative influence on both the formation and functionality of the biofloc, obtaining even higher production rates.     

Crude protein levels in diets for two growth stages of Nile tilapia (Oreochromis niloticus) in a biofloc system

Biofloc technology (BFT) provides an additional feed source for aquatic organisms through the conversion of waste in microbial flocs. Because of this, the suitable protein level in a diet for animals in this system could be different from those in conventional systems. Our objective was to determine the suitable protein level in the diet of Nile tilapia juveniles reared with BFT. Two experiments were carried out with tilapia weighing ~10 g (first experiment) and about 50 g (second experiment) during 61 and 98 days respectively. Five crude protein (CP) levels (within 17% and 33%) were tested. The increment of CP resulted in a reduction in dissolved oxygen, pH, alkalinity and an increase in dissolved phosphorus, total suspended solids and total ammonium nitrogen. The crude protein level had a significant effect (p < 0.05) on animal performance. The linear response plateau model was the best fit for the final weight and weight gain data in the two growth phases. In conclusion, tilapia juveniles of 10–60 g and 60–230 g in biofloc can be fed on diets with 28% of CP (26% of digestible protein) and 22% CP (20% of digestible protein) respectively.     

Effects of three carbohydrate sources on water quality,water consumption,bacterial count,growth and muscle quality of Nile tilapia (Oreochromis niloticus) in a biofloc system

This study compared the effect of three sources of carbohydrates: sugar, wheat and malt flours, on water quality, water consumption, bacterial load, growth and flesh quality of Nile tilapia. Adults (120.6 ± 0.64 g) were stocked in 1.2‐m³ fibreglass tanks at a rate of 25 fish/m³. Carbohydrates were added to the biofloc tanks at a C:N ratio of 20:1. Water flow in the non‐biofloc control tanks was adjusted to 0.6 L/day. The 105‐day experiment was conducted in triplicates. Results showed that biofloc treatments (BFT) with zero water exchange had significantly higher mean total ammonia, nitrites, nitrates, alkalinity, total suspended solids and lower pH than the control treatment. The sugar BFT had the highest floc volume. Growth parameters and feed conversion ratio did not differ significantly among treatments. However, tilapia in the malt flour and control treatments had close values. Gross fish yield was higher (p < .05) in the control than the BFT treatments. Water consumption/kg tilapia produced in the control was 42 times higher than the BFT groups. Protozoa dominated the biofloc biota, and wheat flour was the best in harbouring higher bacterial populations in the gut. Protein content and ∑n‐3 fatty acids were highest in the wheat flour biofloc, while malt flour biofloc had the highest lipids. The sugar biofloc had the highest n‐3/n‐6 ratio. Tilapia muscles in the malt flour and control treatments had the highest protein and lipid contents respectively. Tilapia muscles in the wheat flour BFT had the highest ∑n‐3 fatty acids and n‐3/n‐6 ratio. It can be concluded that farming tilapia in BFT using malt or wheat flours as carbon sources is more economical in saving great amount of water with minimal discharge of pollutants without affecting tilapia growth or flesh quality.