The development of aquaculture in the world has hugely increased from a production less than one million tons in the early 50's up to 60 million tons in 2010. The estimated value is $119,400 million.
Nowadays, tilapia culture is the biggest animal protein source and its consumption is increasing in many countries, especially in developing and industrialised countries.
According to the FAO, the tilapia production in South America is 18,000 million tons (third global position, following Asia and Africa). In Peru, tilapia production is one of the most important in land based aquaculture.
Tilapia has many features that make it good to be farmed. Some of them are: its hardiness, its high resistance in adverse environmental conditions or overpopulation, ability to resist low oxygen levels, high feed conversion rate and high acceptance by consumers.
In Peru, pond production is the most common production system. Tanks and cages are used too, but to a lower extent.
In monoculture production systems, tilapia is fed with manure. Manure provides nutrients that promote the growth of phytoplankton, which contains the necessary proteins to feed tilapia, which filter them. This feeding allows fish to grow to a weight between 200g and 500g within 5 months. In order to grow bigger fish and get a better market price for them, feed (meals) are needed.
Tilapia resistance and adaption ability to a wide range of culture systems has allowed marketing tilapia production in more than 100 countries. In the coming years, its production is likely to grow due to its widespread consumption in many areas.
That is the reason why it is aimed to achieve mechanisition in tilapia farming in ponds.
Materials and Methodology
Two concrete ponds were used: a pre breeding pond (3 x 7 x 1.5 m) and a fattening pond (8 x 20 x 2.5 m). The volumes were 25 and 280 m3, respectively. (Figure 1 in original document).
Weed fish buying and acclimatization
With the aim of developing a semi-intensive tilapia culture, 4,000 fry were bought from Fish & Aquaculture in Moyobamba (San Martín department). Fish weight average was 0.87g and their average size was 3.13 cm. Firstly, fries were transported by land for 18 hours to Trujillo city. Afterwards, they were acclimatized to environmental and feed conditions in a 500-litre fibreglass tank for 48 hours (figure 2 in original document). Secondly, they were taken to Palo Blanco in Cascas city.
Weed fish transport
Moving from Trujillo to Cascas was done by land for 3 hours. Weed fish were packed in appropriate plastic bags (density: 200 fries/8 water litres) in addition to an extra source of compressed air. They were sealed and packed in tecknoport boxes (2 plastic bags per tecknoport box) in order to guarantee survival. (Figure 3 in original document).
Once the fry arrived to the culture area, bags were unpacked and placed in the concrete ponds until a temperature balance between the environment and the bags was reached in order to carry the stocking out.
The density in the pond was 160 fry/ m3, for 40 days. Afterwards, juvenile fish were moved to the fattening pond (density: 12 juvenile fish/ m3) until reaching 320g average weigh.
Feeding was based on artificial extruded feed (Purina brand) and natural feed by fertilization (bovine manure, 1kg/ m3). Feeding rate for artificial feed was initially 5% although it was modified depending on the culture development. Feeding frequency was 3 times a day.
Samplig was carried out monthly. Data recorded were: total length by using an ichtyometer and total weight by using a battery-powered digital scale (Figure 5 in original document). 50 samples were taken.
Water quality assessment
Daily records were taken for main physical and chemical parameters. To register temperature, a 1ºC-precision mercury thermometer was used (range from -10ºC to 120ºC. To determine dissolved oxygen, Winckler method was followed. Finally, pH was determined by using a pH-HIDRION paper.
During the 11-month culture period, weights from 0,87g to 320.41g were reached. Size (length) ranged from 3.13cm to 27.36cm (table 1 and figure 6 in original document).
Initial biomass was 3.48kg. After the first month, it increased up to 9.34kg. By the end of culture period, 897.15kg were reached (figure 7 in original document).
Total feed amount provided to the fish was 1,143.94kg and it varied depending on the fish needs. The average feed conversion rate was 1.65:1.
The relation between weight and length clearly described a power regression model. The value for coefficient of determination (r2) was 97%, which shows a high growth rate was 29.05g/month.
Final survival percentage was 70% (figure 9 in original document).
During the culture stage, main physical and chemical parameters in water remained almost constant, only slight fluctuations were recorded. Average water temperature values ranged from 20.8ºC to 24.5ºC (figure 10 in original document). The dissolved oxygen ranged from 4.5 to 6mg/l and pH remains constant around 7.
In aquaculture, biological knowledge about species growing in the culture is crucial. This knowledge allows explaining anabolism and catabolism, two opposed tends that are directly influenced by temperature, salinity, oxygen, feed, competitiveness, etc.
For instance, in figure 6, it can be observed that Oreochromis niloticus growing is moderately speeded up, possibly due to the water temperature in the region (figure 10). This is because of the fact that optimal temperature ranges from 26 to 30ºC. It could also be due to some additional feed provided to the animals. Olvera (reference entry number 10 in original document) points out that feed are required along all the culture stage in order to get bigger fish and a better market price.
According to figure 7, biomass is gradually increasing along the culture stage. Biomass shows an opposed trend to feed rate because it was complemented with natural feed items. This confirms Kubitsa (2000) affirmations about tilapias feeding from a wide range of natural items when they are cultured in a natural environment. In those ponds that have external supplements, natural feeding only supplies with 30-50% of the total amount of feed.
Moreover, it needs to be taken into account that fertilisation strategies in ponds allow many benefits in aquaculture such as weight increases because manure brings many nutrients that promote phytoplankton growth, which is appropriate for species like tilapia.
Regarding the relation between weight and length (figure 8), a power regression model is clearly described. The coefficient of determination is r2= 0.974 and correlation is r=0.986. This shows a high dependence between the assessed variables, having a slope b=2,479. The described growing here is slightly allometric, possibly due to temperature and the type of feeding employed in the experiment.
Survival described in figure 9 is placed in acceptable ranges.
Regarding the main quality water parameters, temperature is the most important given that it influenced feed consumption and feed rate conversion efficiency. Those will impact on survival and growing. In this experiment, temperature was the reason why a higher growth was not reached.
• In an 11-month semi-intensive culture for Oreochromis niloticus, average weight was 320.41g and average length was 27.36cm.
• Average conversion feed rate was 1.65:1 and final survival rate was 70%.
• Average temperature values ranged from 20.8ºC to 24.5ºC, dissolved oxygen ranged from 4.5 to 6 mg/l and pH was around 7.
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