The fishes of the family Mullidae popularly called as goatfishes contribute
to an important demersal fishery in Visakhapatnam fishing harbour landings.
Study of food and feeding habits are of fundamental importance in understanding
the growth rate, gonadal maturity and other metabolic activities. The
present paper deals with food and feeding habits of U. vittatus
which is based on material sampled from Visakhapatnam fishing harbour
during January 2006 to December 2006. Among the goatfishes U. vittatus
along with U. moluccensis occupies an important position in the
trawl catches at Visakhapatnam fishing harbour.
Studies on some aspects of biology of goatfishes have been reported from
various regions of the world as that of Munro (1983), Russel (1983), Boraey
and Soliman (1984 and 1987), Wahbeh and Ajian (1985), Vassilopoulou and
Papaconstantinou (1992), Reuben et al. (1994), Jayaramaiah et
al. (1996), Labropoulou et al. (1997) Ali and Gopalakrishnan
(1998) Bhargava and Somvanshi (1998) Platell et al. (1998) Ismen
(2005 and 2006) and John and Michel (2006).
The striped goatfish, U. vittatus of Family Mullidae is a commercially
important demersal species living mostly in sandy or muddy sand bottoms
ranging from 5 to 100 m depth. Bulk of the catch is obtained from bottom
trawls. In Upenoids the presence of a pair of barbels just below the symphysis
of lower jaw, attached to the tip of ceratohyal suggests the bottom feeding
habit of these fishes.
MATERIALS AND METHODS
Samples for the present study were collected at weekly intervals from
the mechanized trawlers which were operated off waltair and the catches
were landed at the Visakhapatnam fishing harbour. The study is based on
examination of 636 specimens collected during the study period i.e., from
January 2006 to December 2006. The data on total length, weight, sex,
stage of maturity of each fish were recorded immediately after collection
of the sample. A total number of 636 guts were analysed for the food items.
The stomachs were dissected out and each stomach was preserved in 5% formalin.
The contents of each stomach were washed in a petridish. Various methods
are in prevalence in the studies of stomach analysis of fishes and these
were critically discussed by Hynes (1950).
The identification of food organisms were based mainly on broken shell
remains, partially digested crabs, prawns and teleostean fishes. The gut
contents were grouped as shrimps, crabs, teleostean fishes, mollusc shells
and unidentifiable food items. Some of the food items could not be identified
due to mutilation and they were grouped under unidentifiable food items.
Depending on the extent of distention of stomach and amount of food in
it, the stomachs were classified as full, 3/4 full, 1/2 full, 1/4 full
trace and empty and the points were allotted as 100, 75, 50, 25 and 0,
respectively. The percentage occurrence of different food items was determined
from the total number of occurrence of all items in each month. To evaluate
the importance of each food item, the AIndex of Preponderance@ proposed
by Natarajan and Jhingran (1961) was followed. The monthly averages obtained
by Volumetric and Occurrence methods were substituted in the following
formula and the AIndex of Preponderance@ values were worked out as
I = (100 * V * O)/Sum of (V * O).
Where, I is the Index of Preponderance of food items, V and O are its
percentage of volume and occurrence, respectively. The specimens present
in the present investigation with stomachs classified as full, : 3/4 full
1/2 full were considered as actively fed and those under the category
of 1/4 full and empty were considered to be poorly fed.
A preliminary segregation of stomach contents revealed that the food
items mainly include shrimps (31.56%) crabs (27.93%), teleostean fish
remains (14.51%), bivalve molluscs (13.51%) and the remaining (12.49%)
consisted of unidentified food items. The prawns encountered in the stomachs
were mainly Acetes sp. Some of the teleostean fish remains were
identified as fry of Megalaspis sp. But most of the teleostean
fish remains could not be identified since they were found in advanced
stage of digestion with only the skeletal remains.
Monthly Variations in Feeding Habits
Shrimps formed the main and important food item throughout the year,
crabs were found to be the dominant food item during the month of October
while bivalve molluscs formed the major food item during the month of
January, February and December. The occurrence of bivalve mollusc shells
was not noticed during any other month of the study period.
Variations in Food and Feeding Habits in Relation to Size
It was observed that the food items were less diverse in smaller size
groups. Shrimps i.e., Acetes sp. and crabs formed the major food
items in the fishes below 135 mm in length. Whereas in fishes above 163
mm, food items mainly constituted shrimps i.e., Acetes sp., crabs
and teleostean fishes. The study revealed that the frequency of intake
of shrimps i.e., Acetes sp. and crabs were more or less same among
various size of fishes but the incidence of teleostean fishes were more
in fishes above 163 mm in total length.
Intensity of Feeding
For the study of intensity of feeding, the guts of the fishes were
classified into various categories designated as full, : 3/4 full, 1/2
full, 1/4 full and empty depending on the degree of fullness. Percentage
occurrence of guts in various degrees of fullness is given in Table
|| Percentage occurrence of guts in various degrees of
fullness in U. Vittatus from January 2006 to December 2006
|| Percent frequency of dominant food components from
January 2006 to December 2006
Fishes with high percentage (39.32%) of full guts were found mainly during
the month of January of the study period. Thus the fishes seem to have
actively fed during the month of January. Fishes with average feeding
intensity (50.00%) were found during December of the study period.
Percentage Frequency of Food Items
Percentage occurrence of individual food items is calculated separately
and is given in (Table 2).
Shrimps (Acetes sp.)
The percentage frequency of Acetes sp. was highest with 60.00%
during June = 06 and lowest with 6.56% during December = 06.
During August = 06 the percentage frequency of crabs was highest with
45.83% and lowest with 5.79% during the month of Dec = 06. Among crustaceans
shrimps and crabs formed the main food of this species in almost all the
Teleostean Fish Remains
Percentage frequency of teleostean fishes was higher with 42.11% during
November = 06 and lowest during April = 06 with 3.38%.
Percentage occurrence of bivalve molluscs was higher during December
with 82.45% and lowest during February with 36.47%.
Unidentifiable Food Items
Certain food items during the study period could not be identified
due to the advanced stage of digestion. This was noticed in the months
of March, April, May, July, Aug. and Oct. during the study period.
The results of the present study revealed that U. vittatus is
a carnivorous species feeding mainly on crustaceans and teleostean fishes
and occasionally on bivalve molluscs. The various components of the food
spectrum indicate that the species mainly feeds on benthic and sub-benthic
organisms detected by chemoreceptor rich barbells present on the chin.
Goatfishes feed on small benthic crustaceans, worms, molluscs and small
fish (Vassilopoulou and Papaconstantinou, 1992; Labropoulou et al.,
1997; Platell et al., 1998).
The composition of the diet indicated that the fully adult fishes were
carnivorous, feeding on small crustaceans, mainly teleosts. Bivalve molluscs
also contributed to the diet during some of the months of the study period.
Jayaramaiah et al. (1996) reported that U. vittatus from
Mangalore coast is a carnivore feeding mainly on prawns and teleosts.
In our present study, the same species from Visakhapatnam coast mainly
feeds on shrimps, crabs, teleosts and bivalve molluscs. In both the coasts,
Acetes sp. is the major component among shrimps. Fry of Megalaspis
(teleosts) were found in U. vittatus from Visakhapatnam coast whereas
Stolephorus sp., Leiognathus sp. and Platycephalus
sp. were predominant from Mangalore coast.
The emptiness percentage and stomach fullness indices are very important
to assess feeding intensity. Most mullids feed primarily on polychaetes
and crustaceans; however considerable differences have been found in the
diets of different species (Hobson, 1974; Platell et al., 1998).
Platell et al. (1998) reported that the crabs increased in importance
for the mullid U. lineatus. Wahbeh and Ajain (1985) observed that
the most important prey of P. barberinus were crustaceans and also
that the bivalves became an increasingly important component of the diets
of the larger size classes of mullid Parupeneus barberinus from
Gulf of Aqaba. Russel (1983) studies on food and feeding habits of rocky
reef fish of north-eastern New Zealand reported that U. lineatus feeds
predominantly on small crustaceans.
Randall (1967) reported that the mullids feed primarily over muddy or
sandy bottoms upon surface or sub-surface dwelling invertebrates. The
long barbels are swept over or through the sediments and are presumably
receptive to contacts with prey animals. He also observed that the stomach
contents of Parupeneus maculates consisted of crabs, shrimps in
higher percentages, polychaetes relatively low percentage and in case
of Mullus martinicus crabs, crab larvae, Pelecypods, shrimps, shrimp
larvae and ophiuroids were observed.
The present investigation suggests that the nature of food of the species
is size dependant to some extent. Fishes of bigger length groups, more
often ingested crabs and teleosts in large quantities than those in smaller
length groups. The occurrence of active mobile benthic organisms like
shrimps, crabs and teleosts in bigger size fishes indicates that larger
fish feed very close to or near the bottom. Slight differences in the
feeding habits of mullids from various regions have been noticed, this
can be attributed to the nature of substratum in each locality.
As seen from the results, it could be inferred that U. vittatus
from Visakhapatnam coast mainly feeds on crustaceans, teleostean fishes,
bivalve molluscs. The percentage occurrence of different food items in
the diet shows that the fish selects its food among the bottom living
organisms and the first preferable food item was the shrimp. Thus, the
present investigation revealed that U. vittatus is a demersal carnivore,
whose diet is mainly composed of crustaceans (shrimps and crabs), teleostean
fishes and bivalve molluscs.