Flat fishes and their fisheries

FLAT FISHES &
THEIR FISHERIES
MUNEER .A
Dept. of Aquatic Biology& Fisheries
Muneer.fantasy786@gmail.com
Marine Fisheries

• Flatfishes- the common name of the order Pleuronectiformes,
found in all seas.
• These are generally spiny-finned, deep-bodied, laterally highly
compressed fishes with about 570 extant species
• Unique type of fishes due to its flatness and position of eyes
• Both the eyes are placed in one side, either left or right
• Also have some adaptations like pigmentation in the body
corresponding to the surroundings
• Certain species have commercial importance in some area.
• From these, eleven genera and 25 species of flatfishes
contribute to minor or major fisheries along the Indian coast.

• Order Pleuronectiformes, or Heterosomata consist of 570 extant
species, recognized approximately 11 families of 123 genera.
• Flat fishes are popular under the common names halibut, plaice,
turbot, flounder and sole.
• The flatfishes are found in all the seas of the world and the
species composition is different in different regions.
• The characteristic features of flat fishes are their asymmetry,
mainly their eyes, both eyes on the same side of the head in
juveniles and adults.
• Eyes are on left side in Psettoididae, citharididae, bothidae ,
achiropsettidae, scophthalmidae, paralichthyidae and
cynoglossidae. On the right side in pleuronectidae, samaridae,
achiridae and soleidae.

HABITAT
• inhabit on the continental shelf with shallow, soft
sediments to a depth of about 200 m, also some species
are found in greater depths to about 500 m or more.
• Flatfishes generally lie on the bottom on their blind side.
• They are bottom-dwelling predators, usually found either
lying on top of the substratum or partially burrowing
partially or almost entirely in sand or soft mud with only
their eyes protruding above the substratum.
• found on a variety of substrata including silt, mud, sand
and sand–shell mixtures, with some species also
occurring on rocky or pebbly bottoms.

• All flatfishes begin life as pelagic, bilaterally symmetrical
fishes, during larval growth in a few weeks; they are going
through a magnificent ontogenetic change where one eye
migrates from one side of the head to the other at end of
pelagic larval stage.
• Their bodies flatten into an oval shape, one side turns dark
and one side light, and they settle to the bottom of the sea
floor.
• This metamorphosis occurs very rapidly.

• Later more changes occur from a regular symmetrical body
in various external and internal structures in the skeletal
and digestive systems,
• including placement of nostrils on the head, differential
development of bones in anterior head skeleton,
• differences in jaw shape and dentition on either side of the
body,
• degree of development of lateral body musculature,
• lateral-line development on either side of the body,
• differential coloration on ocular and blind sides, and
• differences in paired fin development on ocular and blind
sides of the body.

ADAPTATIONS
• One of the distinguishing features of the order is the
presence of protrusible eyes- adaptation to living on the
seabed
• The extension of the dorsal fin onto the head.
• All of the flatfishes have a single long dorsal and anal fins
on each edge, both without spines;
• Well-developed ventral fins which are either on the right-
hand edge or on the left-hand edge as the fish lies.
• Most of the species have pectoral fins, one on eyed side
and the other on the blind side.

• The ventral fins are in front of the pectorals or in line with
them
• the abdominal cavity is very short
• While one of their eyes migrates around the head until
both the eyes finally come to lie close together
• The mouth retains its original position more nearly, so
that it is often described as opening sidewise.
• The underside of the flatfish is pale and the top is colored
to match the environment;
• some species are able to change their pigmentation,
especially the flounders.

FOOD& FEEDING
• Flatfishes are generally carnivorous in nature.
• Mainly feed on the bottom-dwelling organisms
• The dietary components of Malabar sole can be grouped
under major categories like polychaetes, amphipods,
copepods, mysids, small molluscs and detritus.
• Among polychaetes , Prionospia pinnata was found to be
the favorite food as this item was noticed in all the
months.
• This indicate- Malabar sole is a typical bottom feeder
mostly feeding on detritus and macro-benthos.
• P.erumei - feeding predominantly on fishes and
cephalopods with crustaceans and bivalves contributing
the subsidiary food.

REPRODUCTION
• A flatfish, as a group, produce a wide variety of egg and
larval forms in the plankton.
• Most flatfish species produce pelagic eggs sizes in range
from 0.5–0.8 mm
• Spawning season varies among flatfish families in
relation to latitude.
• For example, in Pleuronectidae reproduction is restricted
to summer in high latitude waters, while it shifts to
spring and winter in temperate waters.
• But, Soleidae are distributed at lower latitudes and
spawn mainly during summer.

• Most species are having one single spawning period
during the year, some flatfish species spawn bimodal.
• The Malabar sole, C.macrostomus has a prolonged
spawning period extending from October to May off
Mangalore and Calicut and peak time is October to
December.
• As in the case of C.dubius, from October to December.
• C.macrolepidotus spawns during January-February and
August off Rameswaram.
• P.erumei has a short spawning period during September
and October off Mumbai.
• Most flatfish species are batch spawners that are they
release batches of eggs.

• The relative fecundity-
• Cynoglossus macrostomus: 6,540 -19,890 eggs
• P.erumei : 31,380 -12,19,080 eggs
• Flatfishes generally spawn in water deeper than their
juvenile nurseries
• The size of larval flatfishes at-hatching can vary from
about 2mm to 16 mm and size-at-transformation varies
from about 8 mm to 72 mm in various species.
• Flatfish larvae are weak swimmers in the plankton.
• Peak recruitment of C. macrostomus occurs in
September and October off Mangalore; and of C.
macrolepidotus, during March and September off
Rameswaram.

GROWTH AND LIFESPAN
• Cynoglossus macrostomus attains 110 mm and 135 mm at
the end of I and II year, respectively.
• The longevity is about 3 years.The length at first
maturity is 100 to 120 mm, which is about 51% of the L.
• The length at first maturity of C. dubius is 287 mm, which
is nearly 60% of the L. Psettodes erumei attains 220 mm,
420 mm and 550 mm at the end of I, II and III year,
respectively.
• The life span of P. erumei is 4 years.

COMMON SPECIES OF
FLATFISHES IN INDIA

Pseudorhombus arsius
(large tooth flounder)

Cynoglossus bilineatus
(four lined sole)
Pseudorhombus malayanus
(Malayan flounder)

Cynoglossus dubius (Carrot tongue sole)
Cynoglossus lida (Southern tongue
sole)
Cynoglossus semifasciatus
(Bengal tonguesole)

• Globally, Catches of flatfishes stable in recent years with 2% of
total landings.
• Flatfishes belonging to 11 genera and 25 species contribute to
minor and major fisheries along the Indian coast.
• The flatfish landings have increased consistently during the past
few years and reached 53116 t and accounted for 6.22% of total
marine demersal fish landings
• Among all the species of flatfishes occurring along the Indian
coast, it is only the Malabar tongue sole, Cynoglossus
macrostomus that has formed a major fishery for several years,
• especially along the southwest coast and documented at least
from the beginning of this century from the region between
Mulki in Karnataka and Kollam in Kerala.

• This is the important zone for the Malabar sole.
• Commonly called nangu in Kerala also called manthal in some
places of Kerala
• This is the most valuable flat-fish commercially in Indian waters.
• The fishing season is from late august or September to
December and the heaviest landings are in the region between
edakad and kadapuram on the Kerala coast.
• The bulk of the catches are obtained at the commencement of
the season.
• The sudden appearance of the tongue-soles in the surface and
subsurface waters of the inshore region is phenomenal and is
known in Kerala as Manthayilakom, when they are captured in
huge quantities in boat-seines (thattum vala, paithu vala), cast-
nets and shore seines (noona vala).
• In the peak of the fishery, 75 to 80% of the fish are fully mature
begin to disappear as suddenly as they appeared at the
commencement of the season.

• Psettodes erumei is an important food fish and occurs in small
quantities on both the east and west coasts of India, and also
occurs in deeper waters.
• It forms an important fishery at Maharashtra andTamilnadu
coast.
• Where it is much valued as a food fish.
• It grows to a length of 60 cm, being the largest flatfish of our
area; the zero, one and two year-classes constitute the fishery.
• Cynoglossus dubius, Carrot tongue sole came into some
prominence in the fishery only after the introduction of
mechanized fishing along the Kerala coast.
• This species grows to more than three times to be normal
adult size of the Malabar sole.
• Other flatfishes landed in Indian coast have very little
commercial importance .

GEARS
• During the pre-mechnised period, the important gears
used were: cast nets, boat seines (Paithu vala) in Kerala
and shore-seines (rampani=airampani) in Karnataka.
• Certain other gears namely Nethel vala, Pattamkolli vala
and Chooda vala also were used to harvest the sole.
• introduction of mechanization from the sixties, the fishing
pattern has changed, from capturing the shoals at the
surface and subsurface regions by indigenous gears to
effective capture by bottom trawlers.
• the bulk of the Malabar sole caught is by this gear with a
mesh size of 15 to 25 mm operated mostly from small
trawlers of 14 m OAL in the depth zone of 10-50 m

PRODUCTIONTRENDS
• The flatfish landings have increased consistently from
2000t in 1951 to 53,116 t in 2014.
• The maximum landing of 63,353 t was in 1992.
• The resource contributed to 1.4% of the total marine fish
landings and 6.22% of the total demersal landings in
India in the year 2014 (CMFRI).,
• Includes 1784 t of Halibut, 244 t of Flounders and 51088 t.
of soles during 2014
• That is, Soles alone contributed to 96.18% of the total
landings of the flatfishes, followed by the halibut (3.4%)
and the flounders (0.4%) in the year 2014.

• In Kerala, an estimated 12318 t of flatfish was landed in
2014; catch declined by 4.25% from 2013 and formed
15.17% of the total demersal landings of the year.
• C. macrostomus (78.4%) remained the most important
species in the fishery in all gears followed by C.
macrolepidotus (10.9%) and C. bilineatus (10.7%).
• Length range of C. macrostomus in the fishery was 22 to
178 mm with recruitment in April-May and November.
• Fecundity estimated for the species during this period
was 22458 to 52487 eggs.
• The exploitation rate of C. macrostomus was estimated to
be 0.63. [CMFRI]

• The substantial increase in the flatfish landings is due to
the intensification of trawling, which is the most effective
method of exploiting this resource.
• Moreover, the trawl operations are known to transform the
sea bottom that is rich in vegetation and invertebrates to
one of sandy wastelands, which have proved to be ideal
habitat for flatfishes.
• In the intense trawling grounds in several temperate seas,
it is reported that the flatfishes thrive well and the landings
of the flatfishes increased despite decline in the landings
of other demersal fishes.

2005,
35.9
2006,
38.9
2007,
41.8
2008,
39.4
2009,
41.0
2010, 46.8
2011, 62.8
2012,
62.6
2013, 63.2
2014, 53.1
2004 2006 2008 2010 2012 2014 2016
Flatfish landings 2005-14 ('000 tonnes)
Flatfish landings 2005-14 ('000 tonnes)
Source: CMFRI annual reports 2006-07 to 2014-2015

GEAR-WISE LANDINGS
• During past mechanization, the Malabar sole
Cynoglossus macrostomus was caught by cast nets, boat
seines and shore seines.
• With the introduction of mechanization, especially the
trawlers in the early 1960s, the fishing pattern changed
from capturing the flatfishes during their halt at the
surface and sub-surface waters to effective utilization at
the bottom.
• During 1998-2000, the trawlers contributed to 86.7% of
the flatfish landings along the Indian coast.
• Mini trawls (9.6%), dol nets (1.5%) and drift gill nets
(1.0%) were the other gears, which contributed to the
fishery.

SPECIES COMPOSITION
• Among all the species of flatfishes occurring along the
Indian coast, it is only the Malabar sole, C.macrostomus
that has formed a major fishery mainly in kerala-
karnataka coast
• where as Cynoglossus bilineatus dominated (94%) the
fishery in the southern part ofTamil Nadu.
• A larger growing species C. dubius also contributes to a
minor fishery along the coasts; and
• small numbers of species such as C.lida,C. punticeps, C.
bilineatus, C. arel, Paraplagusia and Pseudorhombus are
reported to appear in small quantities in Karnataka.

• Species of Solea, Synaptura and Pseudorhombus are
occasionally taken in small quantities from inshore
catches, especially S. ovate, Pseudorhombus arsius and
Psettodes erumei, (Indian halibut) occurring in small
quantities along both the coasts and recorded from
deeper areas also.
• Along the east coast P. erumei and C. arel, C. bilineatus,
C.punticeps are found in landings.
• P.erumei and Pseudorhombus and Heteromyceterias at
mandapam;
• while the other species that have occurred there
seasonally are C. lida, Pseudorhombus malayanus and
Laepos nigrescens.

LENGTH COMPOSITION
• The length range of C.macrostomus was 40-169 mm in
the trawl landings at Mangalore, Calicut and Cochin.
• The annual mean length ranged from 90 to 127 mm.
• The length range of C.bilineatus was 111-380 mm and
• the mean annual length was 198-205 mm, and
• C.macrolepidotus was 90-420 mm indicating an annual
mean length of 237-243 mm.

UTILIZATION
• Most of the flatfishes have unique taste and have low fat
content and have white flesh.
• So this fishes have food value globally.
• The meat from a flatfish typically varies in color, fillets
from the bottom (white) side of the fish will be thinner
and whiter, while fillets from the top (dark) side will be
thicker and grayer.
• Large-sized flatfishes such as the halibut there is
demand in the market, small sized species like the
Malabar sole have less preference.
• About 90% of the small-sized flatfishes are salted and
sundried and sold during non-fishing seasons.

MANAGEMENT
• No evidence of overexploitation of flatfishes along the
Indian coast, it is essential to adopt a precautionary
approach for sustaining the stocks.
• However, no fishery targets the flatfishes and they are
by-catch of the trawls.
• The bulk of the catches for these resources are
bycatches in the fisheries targeted for other resources
such as shrimps.
• The effect of fishing on the stock of Malabar sole
available at Calicut is negligible and that the present
fishing effort there can be Increased two-fold ,

• However, the studies undertaken at Mangalore Indicate
that the present exploitation rate there for Malabar sole
is about the optimum.
• Studies on yield -mesh curve at Mangalore also indicate
that any change from the present length will only reduce
the yield per recruit.
• Unwanted catches throughout the year may cause the
exploitation of flat fish juveniles;
• it’s affect the recruitment of fishes, so causes the
degradation of population.
• Hence, it may not be possible to implement management
measures exclusively for the flatfishes.

• The management of flatfish stocks could be a part of an
ecosystem based fisheries management consideration,
wherein ecosystems may be delineated based on the
carrying capacity vis-à-vis exploitation,
• and the climatic, hydrographic and biological
characteristics of each ecosystem.
• Eco-groups may be identified in each ecosystem based
on their habitats and their trophic level; and
• The appropriate fisheries management option for each
ecosystem, by way of closed season, mesh regulation,
closed area or by demarcating no-fishing zone, may be
implemented depending upon the status of exploitation
of the eco-groups.

CONCLUSION
• The flatfishes are benthic, carnivorous, belong to the
Order Pleuronectiformes have both the eyes on one side of
the laterally highly compressed body, this group include
the flounders, halibuts, soles, plaice, dabs and turbots.
• The flatfishes begin their life as a normal pelagic fish and
occur sudden metamorphosis and one eye migrates other
side and the body become flat, also fish moves to bottom.
• Flatfishes contribute 2% of the total global landings.
• The landings increased after the introduction of
mechanized vessels and gears.

• Major fishery is associated with Malabar sole, it
contribute the ~90% of the total flatfish landings.
• In India, the flatfish landings have increased consistently
from 2000t in 1951 to 53,116 t in 2014.
• contributed to 1.4% of the total marine fish landings
• The maximum landing of 63,353 t was in 1992.
• The management and conservation plans are not
available specifically for flatfishes because this is not a
target group, a bycatch on trawl for shrimp etc.
• But, like any other dimersal fish, flatfishes also face
degradation due to pollution, habitat degradation and
the exploitation of juveniles; this is affect on the
recruitment.

Flat fishes and their fisheries

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