International Journal of Aquaculture, 2017, Vol.7, No.4, 23
-
30
27
months to reach a market size of 300 – 350 g in trout farms of Idaho, U.S.A after being stocked in raceways
when 4 inch long fingerling stocked (Gempesaw et al., 1995). In general, the production level of rainbow trout in
Indian conditions ranges 300 - 500 kg per raceway of the size of 15 m x 5 m x 1 m (45 m
2
) in 12 months.
However, productivity of 1 tonnes / raceway or more has been achieved at government and private trout farms of J
& K, Kullu valley of Himachal Pradesh and also West Sikkim. With regard to stocking density, a flow rate of 4
LPS can support up to 20 kg/m
3
, though higher volume and higher quality may allow stocking densities as high as
35 kg/m
3
. A minimum rate of 500 m
3
per day of water flow is necessary for 1 tonne of trout produced (Stevenson,
1987). With growing intensification of trout culture, flow-through aquaculture systems like raceways and tanks
discharge effluents with enhanced concentrations of nutrients and solids are receiving attention (Green et al., 2002;
Pulatsu et al., 2004; Bartoli, et al., 2007) and biotic communities (Camargo et al., 2011). However following
physico-chemical conditions are always ideal for trout farming (Table 3).
Table 3 Physico-chemical conditions range observed at various trout farms
Physico-chemical parameters
Range
Dissolved oxygen
near saturation (≥ 9 ppm)
Temperature:
>20ºC
Transparency
1.5-1.8 m
Free CO
2
>1.5 mg/l & < 10 mg/l
pH
7.0-7.5
Suspended solids
< 10 mg/l
Alkalinity (as CaCO
3
):
Hardness
50-150 mg/l
Ammonia (NH
3
)
< 0.05 mg/l
Nitrites (NO
2
-
)
< 0.05 mg/l
Nitrates (NO
3
-
)
< 1.0 mg/l
Phosphates (PO
4
-
)
< 0.03 mg/l
B. Breeding strategies for maintaining imported Genetic stocks of rainbow trout in India
The Himalayan aquaculture is mainly depending on introduced fish species i.e., the rainbow trout and the Carp.
Therefore, it is important to manage the introduced stocks on scientific genetic management basis so as to
maintain variability in the stock and minimize inbreeding. We have developed breeding strategies for such species.
Based on the historical records of import and time to time translocation of rainbow trout to different parts of the
country (Singh and Lakra, 2011), it has been worked out based on microsatellite markers that more likely three
different stocks are present in the country
viz
. Himachal Pradesh stock, Jammu and Kashmir stock and Munnar
hill stock (Southern India) (Barat et al., 2015). Other states share the rainbow trout stocks from these three stocks
which have been brought for either building their new stocks or replacing old stocks. Therefore, hatchery
managers and stakeholders are advocated to practice brood raising and breeding practices as per suggestion and
on-farm demonstrations by the ICAR-DCFR from time to time.
C. Nutrition and Feed formulation
It has been recommended that a diet of no less than 35% crude proteins be administered at a rate of 2 - 3% of
bodyweight per day for grow - out stock of rainbow trout. The nutritional value of the feed depends not only on
the quantity but also on the quality of the protein, i.e., its amino acid conformation. Amid acids are the elementary
units of proteins. Several amino acids are essential to fish growth and development and, therefore, must be present
in the feeds. These amino acids are called essential amino acids. Proximate composition of carcass of fingerlings
of rainbow trout reflected that the requirement of Arginine (6.427%) is comparatively higher than the other
essential amino acids. Therefore, better utilization of the protein in the diet of trout should be obtained by adding
ingredient having more Arginine (Fontagné- Dicharry et al., 2017).
However, use of protein for energy is expensive, thus lipids are primarily included in formulated diets to
maximize their protein sparing. Lipids are a highly digestible source of concentrated energy. Dietary lipid level as
low as 10% has been suggested for rainbow trout on the basis of previous studies. Generally, weight gain and feed
