International Journal of Aquaculture, 2017, Vol.7, No.13, 86-93
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to effectively utilize periphyton from bamboo substrate (Amisah et al., 2008). However, such studies using native
fish species in Brazil are very limited. Jaraqui (
Semaprochilodus insignis
), an iliophagous scavenger, has great
potential for substrate-based aquaculture since it consumes periphyton (Santos et al., 2006). Further, this genus
plays an important social role by catering to the needs of low-income population in the Amazon, accounting for
approximately 50% of fish landings in the port of Manaus (Gandra, 2010).
This study was conducted to evaluate the suitability of three locally available plant substrates (bamboo, ambay
and leucaena) in supporting periphyton growth and in turn the performance of jaraqui (
Semaprochilodus insignis
).
2 Material and Methods
2.1 Area of study and preparation of the experimental tanks
The two experiments of 45 and 120-day duration respectively were carried out in 9 and 12 mud-bottomed outdoor
tanks of 100 m
2
size each at the Coordination of Research in Aquaculture (CPAQ) fish farm of the National
Institute of Research in the Amazon (INPA), Manaus, Brazil. The experimental tanks were drained, disinfected
and dried. Lime (CaO) was applied at 30 g/m² to the tank bottom. The ponds were initially fertilized with chicken
manure at 10 kg and subsequently at 5 kg every 15 days. They were filled with water up to a depth of 0.8 m.
Three locally available substrates viz. bamboo (
Bambusa vulgaris
), ambay (
Cecropia pachystachya
) and leucaena
(
Leucaena leucocephala
) tree branches were collected from nearby areas of INPA and transported to CPAQ.
Uniform sized (1.5 m length and 20 cm circumference) substrates were installed vertically in tanks, except those
of the control in experiment 2, at a distance of 1 m each, keeping a margin of 50 cm on all sides. A total of 76
substrates went into each tank.
2.2 Water quality monitoring
Water quality in the culture tanks was monitored by sampling at 30 cm depth in the water column for recording
values of dissolved oxygen (DO), electrical conductivity (EC), temperature, pH, alkalinity, free carbon dioxide
(CO
2
), hardness, nitrite nitrogen (NO
2
), nitrate nitrogen (NO
3
) ammonia (NH
3
) and orthophospate (PO
4
). DO,
temperature, pH and EC were measured on weekly basis, while the rest of the parameters were analysed at 15-day
intervals. A combined digital YSI 85 meter was used to monitor DO and EC, whereas temperature and pH were
measured with a digital YSI 60 meter. All the other parameters were determined by APHA (1992) methods.
2.3 Periphyton biomass estimation
Periphyton samples from the substrates were collected by scraping with the help of a scalpel from an area of 5x5
cm
2
in triplicate from each tank at 15-day intervals. Each sample was mixed in 50 ml of distilled water.
Subsequently, the periphyton solutions were transferred individually to previously weighed falcon tubes and
centrifuged for 15 minutes. The supernatant was discarded and the tubes were kept at 60°C for a period of 12
hours. Thereafter, each tube was reweighed to determine the periphyton biomass (dry).
2.4 Taxonomic and biochemical composition of periphyton
The periphyton sampling for determining the taxonomic composition was made only during experiment 2, at
30-day intervals, following the methodology described by Bicudo and Bicudo (1970). After extraction, the
samples were preserved in Transeau solution (6:3:1 water: alcohol: formaldehyde) in polyethylene bottles.
Taxonomic identification was performed using keys as per Bicudo and Menezes (2006).
The periphyton sample collection from substrates to determine the biochemical composition was done at 30-day
intervals during experiment 2 as described earlier, except that the area sampled was 6 times larger. The samples
were analyzed in triplicate to determine the percentage of moisture, protein and ash as per AOAC (1995). Total
lipid was analysed by the method of Bligh and Dyer (1959). NFE fraction was calculated by subtracting the sum
of the percentages of moisture, protein, lipid and ash from 100 (Hastings, 1976). Energy content was calculated by
multiplying protein, fat and carbohydrate values by factors of 5 (Smith, 1975), 9 and 4 (Hastings, 1975)
respectively. Further, chlorophyll-a content was also estimated (Stirling, 1985).
