International Journal of Aquaculture, 2016, Vol.6, No.19, 1
-
10
3
Table 1 Quality Index Method (QIM) Scheme developed for the assessment of whole fresh Lake Malawi Tilapia (
Chambo
) stored in ice
for 21 days
Quality parameter
Description
Scores
Appearance
Skin
Shiny grey
0
Grey, not shiny
1
Scale
Firm
0
Loose
1
Eyes
Cornea
Very clear (glass-like)
0
Cloudy
1
Milky
2
Opaque pupil
3
Gills
Colour
Bright red
0
Pale red
1
Dull red
2
Brown
3
Smell
Fresh, cut grass, aquatic weed
0
Neutral
1
Musty
2
Mucus
Clear
0
Cloudy
1
Milky
2
Brown-reddish
3
Texture
Backside
Firm and elastic (in-rigor)
0
Soft
1
Very soft/ depression when pressed
2
Belly
Firm
0
Soft
1
Quality Index (QI)
0-16
Intestines, gills, kidney and tissue (muscle/flesh)
One gram of the fish sample from a chosen part was removed, blended and mixed properly in a mortar then
ascetically transferred to a sample vial containing 9 mls of 0.1% sterile peptone water. The vial was closed and
shaken thoroughly for 10 minutes then allowed to standing for 20 minutes, after which a 6 fold serial decimal
dilution was carried out in triplicates. Viable aerobic bacterial counts were enumerated in standard plate count
agar after incubation at 37°C for 48 hours (Slaby et al., 1981). Results were reported in log cfu/g.
Identification of bacteria
Morphological characteristics of the various bacterial isolates were noted in the agar plates, and microscopy. After
staining reactions and several biochemical tests, individual microbial species were identified as described by
Slaby et al. (1981). Representative isolates were re-plated on various selective media to observe their habits and
other specific colony attributes.
2.3 Biochemical analysis
A procedure earlier used by Okoro et al. (2010) modified from Conway (1968) was followed for the determination
of Trimethlamine nitrogen (TMA-N) and Total volatile basic nitrogen (TVB-N).
Determination of Total volatile basic nitrogen (TVB-N)
25 g of the fish sample was removed, chopped and thoroughly mixed in 75 mls of distilled water in a 250 mls
beaker. A few drops of 2N hydrochloric acid (HCl) were added to adjust the pH reading to 5.2 followed by heating
at 70
o
C then cooling to room temperature. When cooled, the sample was filtered into a conical flask using a
Whatman No. 1 filter paper. 2 mls of 0.025N HCl was transferred to the central compartment of the micro
diffusion dish using a pipette then adding 2 mls of the extract and 1 ml of saturated potassium carbonate (K
2
CO
3
)
