observations on the biology of

OBSERVATIONS ON THE BIOLOGY OF LABEO GONIUS (HAMILTON)

t

S. PARAMESWARAN, * C. SELVARAJ 2 AND S. RADHAKRISHNAN '

Pond Culture Unit of Central Inland Fisheries Research Institute, Joysagar, Assam

A B S T R A C T

Observations on the biology of Labeo gonius (Hamilton) in confined waters have been made and the data on the different aspects have been analyzed and discussed.

The length - weight relationship of the species can be expressed by the equation US'=0.000007153 L 3.0865. The monthly fluctuation in the condition factor of the adult fish was found to be related to the maturity cycle.

L. gonius matures within a year. The ratio between males and females was found to be 1:1.052. Macroscopic and microscopic examination of the gonads, ova diameter measurements and gonadosomatic index indicated that mature fish become available from March to August, th© peak being in May. The size frequency of ova in ovaries in different stages of maturity suggested that the species breeds only ones in a year. The statistical relationships between fecundity in relation to total length, total weight and ovary weight and ovary weight in relation to total length have been established.

From an exclusively plankton-feeding habit in the post-larval stage, the species changes over to a column and bottom-feeding habit in the juvenile stage, subsisting on vegetable matter, phyto and zooplankton organisms, mud and sand. The adult fish is predominantly a bottom feeder, the diet consisting of fresh and decaying plant matter, mud and sand, phytoplankton and filamentous algae.

Preliminary experiments indicated that the growth rate of L. gonius is poor in comparison to major carps.

INTRODUCTION

Labeo gonius (Hamilton) is the dominant species of carp found in the natural waters of Assam. This species is cultivated in the ponds of Assam,

Present address: 1. Coordinated Research Project on Air Breathing Fishes, Central Inland Fisheries Research

Institute, Bhadra Reservoir Project, Shimoga District, Karnataka State. 2. Central Inland Fisheries Research Substation, Cuttack 1, Orissa. 3. Central Inland Fisheries Research Unit, 19 A, Patel Road, Madras-11, Tamil Nadu.

OBSERVATIONS ON THE BIOLOGY OF LABEO GONIUS 55

along with the major carps Labeo rohita and Catla catla, in preference to Cirrhinus mrigala, which is not consumed by the majority of people in this state on religious ijrounds. There is, hence a high demand for the seed of L. gonius in the state from fish culturists.

According to Day (1878), the habitat of L. gonius is throughout northern and eastern India, as low as the Krishna in peninsular India, Pakistan, Bangladesh and Burma, .fob et al. (1955) have reported that in Mahanadi tliis fish, tiiou^ found in rapid and slow moving waters, prefers to inhabit shallower portions of the river, where there is plentiful growth of submerged weeds and that economically it does not constitute an important fishery.

This medium-sized carp, like other Indian carps, breeds in inundated rivers during the raonsoon months. The spawning habits of this fish have been studied by Khan (1924) and Ahamed (1936, 1944) and its life-history, by Ahamed (1944) and Mookerjee and Ganguli (1949). The identifying characters of the larval and post-larval stages of the species have been described by Khan (1926), Ahamed (1944), Mookerjee (1943) and Mookerjee et al (1944). Some observations on the maturation and induced breeding of L. gonius have been made in Assam by Parameswaran et al. (1970, MS.). However, there is paucity of published information on the various aspects of the bionomics of the fish-

Observations on the biology of L. gonius and its growth in Assam ponds in relation to other cultivated carps, made during a period of two years commencing from Januiiry 1964 form the basis of the present communication.

MATERIAL AND METHODS

Fortnightly collections of the material were made from the Government fish farm at Joysagar and Nawpukri tank (area about 70 ha), located in the Sibsagar District of Assam. The latter gets connected with the river Dikhow during the rainy season and gets naturally stocked with fish every year. Samples from this source, however, were available only from August to April as there were no netting operations in the tank during the rest of the months.

The total lengths of 1,685 specunens (15 to 435 mm long) were measured to the nearest mm. The fry and juveniles, preserved in 5% formaldehyde, were weighed in a physical balance of 10 mg accuracy. The weights of the adult fish were recorded, in the fresh condition, in an Avery scale of 0.5 g sensitivity.

The specimens were dissected for the gonads and guts, which, after gross examination in the fresh condition, were preserved in 5% formaldehyde and subsequently subjected to detailed studies.

To study the maturity cycle of the fish, 439 specimens varying from 80 to 409 mm in total length, were examined through the various months. The

5 6 S. PARAMESWARAN AND OTHERS

stages of maturity were fixed by the conventional methods of assessment (Para-meswaran et al., 1970). Samples of one hundred ova were measured at random from the ovaries during December to July to determine their average size during the maturing months. For studying the progression of ova towards maturity and the spawning periodicity, five hundred ova from ovaries in stages I to V were measured and their frequency polygons drawn, following Clark (1934). The gonads of the fish were weighed individually to -determine the gonadoso-matic index for different months.

The fecundity of 73 specimens ranging from 188 to 403 mm in total length was studied. The weights of mature ovaries were recorded and the number of ova in two samples of 2 g from each ovary was counted, from which the • fecundity of the fish was computed.

The gut contents of 161 post-larvae (6 to 30 mm long), 107 juveniles (31 to 100 mm long) and 512 adults (101 to 409 mm long) were examined. The guts were uncoiled and their total lengths recorded. The percentage of feed in the guts was determined by the degree of their distension. The entire guts of the post-larvae and the anterior one-third (leaving the broader stomach, which almost always was empty) of the juveniles and adults were dissected and the contents washed into a petri dish. Samples from this were examined on a slide under a microscope and the percentage composition of the various food items was determined by 'eye estimation' (Pillay, 1952).

Preliminary experiments were conducted in ponds of Government fish farm, Joysagar, to study the growth of the species in comparisonwith C. car/a, L. rohita and C. mrigala.

LENGTH — WEIGHT RELATIONSHIP

Since the sexes are not distinguishable externally, excepting during the breeding season, they were not considered separately. The specimens were grouped into 10 mm class intervals and the length — weight relationship was derived using the formula W=cLn (where W is the weight of fish in g, L is the length of fish in mm, c is the initial growth index and n is the equilibrium constant) and was found to be

^=0.000007153 L^°^^^

The observed mean weights were plotted against their respective lengths and a regression line was fitted to the data (Fig. 1, A). Evidently, the fish gains weight rapidly with increase in length, after it has reached a size of 225 mm.

Logarithmically the length - weight relationship can be expressed as log W= -5,1455 + 3.0865 log L (Fig. 1, B). Coefficient of correlation r=0.987.


I.M. n m UMTN M MM

M U * •

- IM .

IM .

TOTAL LINCTH IN HH

FIG. 1. Length — weight relationship of L. gonius.

CONDITION FACTOR 'K ' (PONDERAL INDEX)

The condition factor of the adult fish was determined employing the W

formula K='^'i X 10,000 (where K is the condition factor, J^is the weight of

the fish in g and L, the length in mm). The condition factor for males and females was found out separately (Fig. 2).

It is seen from Fig. 2 that the condition factor shows a definite seasonal cycle and that the fluctuations in respect of the females are sharp, especially during May — August, although the trend in both sexes is more or less same. The value which is least in December, shows a rapid increase from March, readies the peak in May and is maintained at a slightly lower level in June. Thereafter, it shows a gradual fall.

58 S. PARAMESWARAN AND OTHERS

046

0.14

0.12 .

i 0-10 J .

• • FEMALE •-—. MALE

a. J -

J F M A M J J A S O N C

FIG. 2. Monthly fluctuations in the ponderal index of adult L. gonius.

MATURATION OF GONADS

Since Indian carps do not breed in confined waters, the maturity stages corresponding to stages VI (spawning) and VII (spent) do not occur in ponds (Parameswaran et al., 1970). Hence stage VII, in the present study, denotes resorbing gonads.

The percentages of males and females of L. gonius in different stages of maturity during various months are plotted in Fig. 3. By May and June all the males examined were in stage V whereas about 82% and 80% of the females were in stage V. Resorption of ovaries commenced by June and increased rapidly during July and August. By September the gonads of all the females were in different stages of resorption. The ^resorption of gonads in males, however, was found to begin rather late, from late July and occasional oozing males continued to occur till early September.

Emaciated specimens and some of the yearlings maturing for the first time appear to lag behind in maturation and the gonads in many of them seem to begin resorption before attaining full maturity.

The study indicates that mature females of L. gonius become available from March to August and males, from March to September. In either case, the period of peak maturity is during May and June. Obviously, the gonads in males mature early and begin resorption late, as compared to the females.

Progression of ova towards maturity The ova diameter frequency polygons of ovaries in stages I to V are

depicted in Fig. 4.

In the Qvary of stage I, only a single group of transparent ova with mode at 0.051 mm is encountered. In stage II ovary the mode has shifted to

OBSi3RVATlONS ON THE BIOLOGY OF LABEO GONIUS 59

W t n F N F M F m r W F M F M V M F M F Ki F M F

J F M A M J J ~ A " S " O " "N D ~

MATwiTY twMt: ^ l i P-Bl | - Q l t Q I V J BI-VJ jj]]J-vn-FIG. 3. Monthly percenages of L. gonius in different stages of maturity,

(the number of specimens examined is indicated above the respective months)

0.238 mm. In this stage yolk deposition has started only in a few larger ova. The ova of stage III ovary are translucent and partly yolked, with a distinct mode at 0.459 mm. In stage IV (maturing) ovary the ova are opaque with a mode at 0.748 mm. Stage V (mature) ovary has a single group of ova, all mature and witli transparent periphery, ranging from 0.731 to 1.258 mm and having a mode at 1.003 mm.

Progression in the iize of ova during different months The progression in the average size of ova from December to July,

illustrated in Fig. 5, shows that majority of the ovaries become mature by May. Similar indications are obtained also from the study of the stages of maturity and gonadosomatic index of the species during different months (see below).

Gonadosomatic index The gonadosomatic index, which is indicative of the state of gonadial

development and maturity, of L. gonius, calculated separately for males and females and depicted in Fig- 6, shows that it increases steadily frbm January, reaching the peak in May," Which is maintained with a slight decline iii June and, thereafter, falls gradually and becomes least in September.


1 I

2 0-0

IS.0

lao

S.0

M

lao

s«

oo

lao

M

M 104

M

M

I M

M

a«

• ^ A \ V

• A • /V v* ^

•

.^•^w^

i •

- ^ ^

K

J\^ ^ ^^ - -vv .^ .

A _y -.N^^V^—'^ V

. i . - * « , i - » « V ^

ITACM

ITA«M

ITA6C-UI

STAGE-IV

^

m STACE-V

• • * ^

0.17 0J4 O-SI OM 04S 1.02 i-ia

size OP OVA IN MM

FIG. 4. Ova diameter frequency polygons of ovaries in stages I to V of maturity in L. goidus showing their progression towards maturity.

DIFFERENTIATION OF SEX, SEX RATIO AND SIZE AT FIRST MATURITY

Differentiation of sex

Externally the sexes are distinguishable in L. gonius only during the maturing and breeding season; the male develops roughness of the pectoral fin, when the fish is in stages III and IV of maturity. The sexes can also be easily distinguished during the breeding season by the soft, bulging abdomen in the female and oozing of milt by male, on genfle pressure.

Sex ratio

A large number of specimens were sexed externally during March to August (when only the sexes are externally distinguishable) and the monthly ratio between males and females was found to range between 1:0.943 and

OBS13RVATIONS ON THE BIOLOGY OF LABEO GONIUS 61

FIG. 5. Progression in the average Mze of ova through different months in L. gonius.

ZS.0

2 M .

r^•w -i Is

JO

ae r'm .foo r^

04 ;

I

MMTM

FIG. 6. Monthly fluauation in tlM gonadosomatio index of X. gonius.

62 S. PAR^MESWARAN AND OTHERS

1:1.194, the average for the entire period being, 1:1.052 (Table 1). Chi square test indicated that there is no significant difference between the observed and the expected 1:1 ratio (P^O.3).

TABLE 1. Sex ratio of L. gonius during the months March to August, 1964 and 1965.

Ratio Month No. examined Males Females

Male : Female

March April May June July August

Total

160 232 334 307 186 158

1,377

82 109 161 158 89 72

671

78 1 123 1 173 1 149 1 97 1 86 1

706 1

: 0.951 : 1.136 : 1.075 : 0.943 : 1.090 : 1.194

: 1.052

Chi square: 0.8896 P > 0.3

Size and age at first maturity Rearing experiments indicated that L. gonius matures during the first

year of its life. The smallest mature male encountered measured 142 mm and weighed 42 g, while the smallest female was 188 mm in length and weighed 70 g.

FECUNDITY

The average number of ova per g of mature ovary in L. gonius was 1,259.56. The number of ova per g body weight (fecundity factor) ranged from 88.13 to 364.56, with an average of 254.753. Fully mature ovarian eggs are dull bluish green in colour and measure 1020 to 1.224 mm (average) in diameter.

As very little published information is available on the relationship between the size of fish, size of ovary and fecundity of Indian carps from confined waters, an attepipt was made to establish these statistically in L. gonius. Fully mature ovaries only were considered for the study. The specimens were grouped into 10 mm and 40 g intervals for the calculations and the equations were derived using the general allometric formula F=cLn (where F is the factor to be found out, c is a constant, L is the variable involved and n is an exponent) and its logarithmic form log F=log c+n log L. In all cases, the observed relations were plotted and a regression line.fitted to the data. Ovary weight and total length

The relation between ovary weight (Ow) and length of fish (L) can be expressed by the equation

0^=0.0000000077038 L 4.0165


220 300 340 MO 420

TOTAL LENGTH IN MM

FIG. 7. Ovary weight - total length relationship of L. gonius.

The relationship, depicted in Fig. 7, A, is a parabola, indicating that ovary weight increas(5S at a rate more rapidly than the length.

Logarithmically this can be expressed as log Oiv= -8.1133 + 4.0165 log L (Fig, 7, B). Coefficient of correlation r=0.934.

In Fig. 7, B, the observed values for smaller specimens (up to 220 mm in length) congregate below the regression line.

Fecundity and ovary weight The relation between fecundity (F) and ovary weight {Ow) can be ex

pressed by the equation


F=2039.0 Ow 0.8762 (Fig. 8, A).

Fig. 8, A suggests that with the increase in size of the ovary a somewhat corresponding increase in fecundity.

there is

10«< OVAIir WEIGHT M Q

H M 2'9

a*4

I M

tu

• 4

44

4

•

* *

•

•

M

LOC' TOTAL UIKTH III MM

M » »<

/ *F

• /I

* / J

% / ' 1

• 1 * 1 • 1 — 1 1 1 1

^T

-

-

.

-

•

OVAIir MSHT W C

220 UO

TOTtl lENCTH n MM

Fio. 8. Fecundity - ovary weight relationship of L. gonius.

FIG. 9. Fecundity - total length relationship of L. gonius.

The regression of fecundity and ovary weight, in the logarithmic form, can be expressed as

log F=3.3096 + 0.8762 log OH- (Fig. 8, B).

Coefficient of correlation r=0.876.

Fecundity and total length The parabolic relationship between fecundity (F) and total length of

fish (L) was found to be F=0.00016878 L 3.5073

This equation, Ulustrated in Fig. 9, A, is curvUinear. It is evident from the relationship that the fecundity of the fish increases at the 3.5073th power of length.

The logarithmic expression of the equation was found to be log F 3.7727 + 3.5073 log L. Coefficient of correlation r=°0.8677-

OBSBRVATIONS ON THE BIOLOGY OF LABEO GONIUS 65

In Fig. 9, B, depicting the relationship graphically, the observed fecundity values of smaller specimens (up to 220 mm in length) congregate below the regression line.

Fecundity and body weight The relation between fecundity (F) and weight of fish (W) can be

expressed by the equation F=96.288 W 1.1709

14

kSe. TOTAL WEICKT IK C

_ M 24 M

170 270 370 470 570 C70 770

FIG.

TOTAL WEIGHT IN G 10. Fecundity - body weight relationship of L. gomus.

The graphic expression of the equation (Fig. 10, A) indicates that fecundity has a closer relation with fish weight which, in turn, is more directly related to the ovary weight rather than length of fish. Here again, as in the case of fecundity and fish length, the fecundity values of smaller specimens weighing up to 130 g congregate below the regression line, showing that their fecundity in relation to weight is low, compared to larger specimens.

In the logarithmic fcmn the regression equation was estunated to be log F=-1.9833 + 1.1709 log W (Fig. 10, B). Coefficient of correlation r=0.9899.

66 s. PARAMESWARAN AND OTHERS

In all the equations the coefficient of correlation r (ranging from 0.8677 to 0.9899) is very high, which emphasizes the high significance of the relationships.

FOOD AND FEEDING HABITS

The average percentage composition of the different groups in the gut contents of the fish at various length ranges are illustrated in Fig. 11.

100 6-10 MM

60

20

11-20 MM

51-IOOMM

21-30 MM

_lJLiv 101-150 MM 151-200 MM

3I-50MM

20I-409MM

A B C O E A B O D E A B O D E A B O D E

FOOD ITEMS

FIG. 11. Percentage composition of the different food items in the

gut contents of L. gonius at various length ranges. A — Zooplankton; B — Phytoplankton; C — Filamentous algae;

D — Vegetable matter and detritus; E — Mud and Sand.

The post-larvae of L. gonius examined for gut contents were collected from nursery ponds which were stocked exclusively with its spawn or in combination with that of other carps. The smaller post-larvae (6 to 10 mm long) were observed to feed almost exclusively on zoo and phytoplankton, the former constituting the bulk. The zooplankton in the gut contents consisted, in the order of dominance, of cladocerans (39.70%; Moina brachiata, Bosmina sp., Ceriodaphnia sp., Alonella sp.), rotifers (30.40%; Brachionus spp., Keratella sp., Polyarthra sp., Rattulus sp., Monostyla sp.) and protozoans (4.08%; Difflu-gia sp., Arcella sp., ciliates). The phytoplankters commonly encountered were diatoms (3.66%; Gomphonema sp., Navicula spp., Stauroneis sp.) and desmids (2.11%; Staurastrunt'spp., Cosmarium spp., Pleurotaenium spp., Euastrum sp.). The larger post-larvae (11 to 20 mm long) consumed, in addition to the above

OBSliRVATIONS ON THE BIOLOGY OF LABEO GONIUS 67

(cladocerans 50.71%; rotifers 22.59%; protozoans 2.19%; diatoms 5.05%; Chlorophyceae 4.82%; euglenoids 2.16%), copepods (4.83%; Diaptomus spp., Cyclops spp. and thsir nauplii) and small quantities of decaying organic matter and detritus of vegetable origin (3.49%), mud and sand (1.30%) and traces of filamentous algae (0.21%; Oedogonium spp., Oscillatoria sp., Ana-baena spp.). Still larger post-larvae (21 to 30 mm long) subsisted on larger quantities of organic matter (12.56%), filamentous algae (1.35%) and mud and sand (8.39%). It is evident from Fig. 11 that with the increase in the size of post-larvae, the zooplankton diet decreases with corresponding increase in phytoplankton organisms, organic matter, mud and sand.

The juveniles (31 to 1(X) mm long) examined from different rearing ponds were observed to feed mainly on decaying and fresh organic matter of plant origin (44.37%), phyto- (27.24%) and zooplankton (10.52%) organisms, mud (9.45%), sand (6.19%) and small quantities of filamentous algae (2.22%). The bulk of organic matter and mud consumed increased progressively with the increase in size of fish, while that of phyto- and zooplankton, especially the latter, decreased.

The adult fish (101 to 409 mm long) was found to subsist mainly on fresh and decaying vegetable matter (53.29%) consisting of aquatic plants (14.02%) like Hydrilla, Najas and Ceratophyllm, decaying leaves and roots of emergent and marginal plants (39.26%) such as Nymphoides, Trapa and Mar-silia and detritus- Fairly large quantities of mud (17.27%) and sand (6.24%) were found in all the guts examined. Appreciable quantities of phytoplankters (17.91%) and small, though not insignificant, quantities of filamentous algae (4.20%) were also encountered. The percentage of zooplankton, which consisted of copepods, cladocerans and rotifers, however, was found to be negligible (102%). Among phytoplankters, the largest percentage was constituted by Bacillariophyceae (10.76%; Navicula spp., Pinnularia spp., Synedra spp., Gyrosigma sp., Stauroneis sp., Cymbella sp., Achnanthes sp., Gomphonema sp., Surirella sp.), which appear to have been consumed mainly along with the organic matter, detriius and mud from the bottom, followed by Euglenophyceae (3.35%; Euglena spp., Trachelomonas spp., Phacus spp., Strombomonas sp., LepocincUs sp.), Chlorophyceae (2.02%; Cosmarium spp., Closterium sp., Pediastrum spp., Anidstrodesmus sp., Actinastrum sp., Micrasterias sp., Arthro-desmus spp., Euastrum sp., Staurastrum spp., Pleurotaenium spp., Eudorina sp.) and Cyanophyceae (1.79%; Microcystis spp., Anabaena spp., Merismopedia sp).

Examination of the rectal contents of the fish of different size ranges showed that, excepting for the smaller post-larvae (up to 10 mm long), most of the phytoplankters ingested (excepting euglenoids and a few blue-green algae) get digested, indicating that this item iias considerable nutritional value for the fish.

€8 S. PARAMESWARAN AND OTHERS

The study reveals that while the fish in' the post-larval stage (6 to 30 mm long) is a surface and column feeder, it gradually changes over to a mainly bottom and column feeding habit in the juvenile (31 - 100 mm long) and adult stages (101 - 409 mm long).

Intensity of feeding The feeding intensity of the post-larvae and juveniles may be considered

to be fairly high, since the guts of most of them were over 70% full and empty guts were only occasionally encountered.

The fluctuations in the feeding intensity of the adult fish (expressed as percentage of fullness of the gut) during the different months are depicted in Fig. 12. It is seen from the figure that the intensity of feeding of the adult

M J J

MONTH

FIG. 12. Monthly fluctuation in the feeding intensity of adult L. gonius.

(number of specimens examined is indicated above the histogram for each month).

fish also is fairly high. The peak feeding intensity is noticed during August to November and February to April. There is a slackening in the intensity of feeding from May to July and December to January.

Ratio between length of fish and length of gut The ratio between length of the fish and length of the gut for various

size groups are given in Table 2. The gut length increases progressively with increase in the lenglh of fish.

OBSiaiVATIONS ON THE BIOLOGY OF LABEO GONIUS 69

TABLE 2. The ratio between the length of fish and gut length of L. gonius at different size ranges.

Length range (mm)

Ratio between fish and gut length

6 — 1 0

11 — 20

21 — 30

31 — 50

51 — 100

101 — 150

151 — 200

201 — 409

GROWTH

0.816

: 1.046

2.271

5.206

6.466

7.203

8.667

10.422

The data on the approximate length and weight attained during the first and second year by L. gonius, C. catla, L. rohita and C. mrigala in ponds of the Government fish farm, Joysagar (obtained from the farm records), given in Table 3, indicate!; that the absolute growth of L. gonius in terms of length and weight is comparatively very low.

TABLE 3. The range in length and weight attained by L. gonius, C. catla, L. rohita and C. mrigala in ponds at Joysagar.

L. C. L.

C.

gonius Catla rohita mrigala

First year Range in

Lenijth (mm) Weight (g)

165 236 227 218

— 204 — 371 — 387 — 337

45 -218 -128 -

183 -

- 82 - 6 0 6 - 544 - 280

Second Range

Length (mm)

191 — 314 — 292 — 299 —

247 425 394 435

year in Weight (g)

70 620 280 210

— 180 —1400 — 670 — 750

Comparative growth and productivity

To compare the growth of L. gonius with that of the major carps, a preliminary experiment was conducted in two nursery ponds (each of area 0.02 ha) for a duration ol six months- In both the ponds, fingeriings of catia, rohu, mrigal and gonius were stocked at the rate of 6,000 per ha, in the ratio 2:2:1:1. The initial average weight of all the species (excepting catla) in the two ponds was same. The ponds were manured with raw cowdung, at the rate of 1,000 kg per ha per month. The data of the experiment are given in Table 4.


It is evident from the table that the growth rate of L. gonius and the percentage contribution by the species towards total production are very low compared to mrigal (both of which have similar feeding habits), catla and rohu.

TABLE 4. The experimental data on the growth and productivity oj C. catla, L. rohita, C. mrigala and L. gonius {the data

for the two ponds have been averaged and given)

C. catla L. rohita C. mrigala L. gonihs

Average initial length (mm) 90.4 99.6 92.0 85.9 Average initial weight (g) 5.5 7.0 7.0 7.0 Average increase in length in six months (mm) 106.1 68.4 94.9 40.2 Average increase in weight in six months (g) 106.4 41.1 56.6 15.1 Survival in percentage 86.25 77.5 92.5 95.0 Production in kg for six months per pond+ 3.642 1.212 1.032 0.250 Production in kg per ha for six months 182.1 60.6 51.6 14.0 Percentage contribution towards total production 59.0 19.7 16.8 4.5

+ area: 0.02 ha

DISCUSSION

The largest specimen of Labeo gonius examined by the authors in Assam measured 449 mm in length. Hamilton (1822) has stated that the fish attains a length of 458 mm. According to Job et al. (1955) in Mahanadi its average size is 382 mm. The report by Day (1878) that the fish attains a length of about 1,525 mm, a size not normally attained even by the major carps, does not appear to be correct.

Earlier worlcers have observed that the fluctuations in the condition factor are related to the maturity cycle of fish (Hickling, 1930; Le Cren, 1951). This is found to be true in the case of L. gonius also, as its condition factor is maximum during May and June, when majority of the fish are mature and the value declines from July onwards when the resorption of gonads commences (Fig. 2).

Observations on the maturation of L. gonius (Fig. 3) indicate that the gonads begin to develop from October — November and mature fish become available from late March to August, with peak in May and June.

It is well known that the gonadosomatic index increases with the maturation of fish, being maximum during the period of peak maturity and declining abruptly thereafter, when the fish become spent (Hickling, 1930; LeCren, 1951). In L. gonius the gonadosomatic index is maximum during May and June, when the majority of the fish are found to be mature. However, in the present case, the fall in its value is not rapid due to the reasons that the fish does not spawn in confined waters and the gonads are gradually resorbed (Fig. 6).

OBStiRVATIONS ON THE BIOLOGY OF LABEO GO NWS 71

Observations on the average size of ova during the different months (Fig. 5) also indicates that the females are mature during May, June and July.

The study of the seasonal changes in the condition of gonads (Figs. 3, 5 and 6) and ponderal index (Fig. 2) thus clearly establishes that mature specimens of L. gonius are encountered from March to August and its period of peak maturity is during May and June. This has been confirmed by field experiments on the induced breeding of this species (Parameswaran et al, MS.).

Ahamed (1944) has reported that L. gonius breeds in July in the Punjab. According to Mooki rjee and Ganguli (1949) the breeding season of the fish in Bengal is from June to August. In Assam, however, L. gonius and other carps mature earlier in ponds and have been successfully induced to breed by late March and early April (Parameswaran et al., 1970, MS.). The authors have recorded that liverine carps also mature by the middle of March in this State (Parameswaran et al, 1970). A probable reason for the early maturation may be the early onset of monsoon in this region. It may be mentioned in this connection that in Chittagong (Bangaladesh), where monsoon begins early, carps begin breeding in the rivers from April onwards (Hora, 1945; Ahamed, 1948).

From the preisence of only a single size group of ova in the mature ovary (Fig. 4), it may be inferred that L. gonius spawns only once during the season and that all the ova are shed in a single spawning act (Prabhu, 1956; Qasim and Qayyum, 1961) This was further confirmed by induced breeding experiments. In the mature ovary of L. rohita and C. mrigala also, there is only one size group of ova, which are shed in a single spawning burst (Qasim and Qayyum, 1961).

L. gonius attains maturity within a year like the minor carps, Labeo bata (Alikunhi, 1956), Labeo boga (Alikunhi et al, 1962) and Cirrhinus reba (Alikunhi and Rao, 1951).

During the Ijreeding season, the males of L. gonius develop roughness of the pectoral fin. Such a secondary sexual character has been reported in the Indian major carps by Chaudhuri (1959).

A knowledge of the fecundity of cultivated fishes becomes very useful in pond culture investigations in assessing the targets of spawn production, from the available stock of breeders. The fecundity of L. gonius in the size range 188 to 403 mm varied from 9,892 to 229,999. The fecundity factor (number of ova per g body weight) of the species has been compared with that of the major carps and som^ other minor carps in Table 5.

In L. gonius the fecundity increases at a rate substantially greater than the third power of length, as observed by Raitt (1933) in haddock, Hickling (1940) in herring and Simpson (1951) in plaice. As observed by Hickling (1940), the fecundity is directly related to the size of the ovary and fish weight.


TABLE 5. The fecundity factor of L. gonius and some other Indian carps

Species

L. gonius

C. catla

L. rohita

C. mrigaia

L. cdlbasu

L. bat a

L. boga

Fecundity factor

254.753

78,3

142-424

146.9

409.3

285.5-374.9

239-596

Reference

—

Khan, 1934

Alikunhi et al., 1962*

Khan. 1934

Khan, 1634

Alikunhi, 1956

Aiikunhi et al., 1962"

rather than fish length- There is no decrease in the number of ova per unit weight of the ovary with increase in size of the ovary in L. gonius (see Gerking, 1959).

A critical examination of the data on the food and feeding habits of L. gonius at different stages (Fig. 11) shows that the fish is almost exclusively a surface plankton feeder in the post-larval stage (6 to 30 mm long), like other Indian carps (Alikunhi, 1952, 1958). In the juvenile stage (31 to 100 mm long) it gradually changes over to column and bottom feeding habit, subsisting mainly on decaying and fresh vegetable matter, detritus, mud, sand and phy-toplankton. The bottom feeding habit becomes more pronounced in the adult stage (101 to 409 mm long) when over 76% of the food consumed consists of vegetable matter, mud and sand. The ventral mouth, with the terminal, fringed and fleshy lips, also is adapted for picking up food from the bottom. Similar morphological adaptations in the major carps in relation to feeding habits have been described by Mookerjee and Ganguli (1951). The food habits of L. gonius are comparable to those of C. mrigaia (Mookerjee and Ghosh, 1945; Mookerjee et al, 1946; Chacko and Ganapati, 1951; Alikunhi, 1957).

The feeding intensity of adult L. gonius is fairly high (Fig. 12). It is maximum during August to November when the fish are resorbing and February to April, when they are maturing. This may be attributable to the higher temperature and the accelerated physiological activity of the fish during these months. The feeding intensity of the fish is less during May — July, the probable reason for this being that the feeding activity slackens when the fish are fully mature and again December — January, which may be due to the low physiological activity of the fish during these extreme winter months.

According to Mookerjee and Das (1945) and Al-Hussaini (1947), there is a correlation between the food habits and the ratio between the length of fish and that of the intestine in different species. The length of the gut is


almost equal to or in some cases less than the length of the fish in carnivores, while in herbivores, it is longer, the increase being proportionate to the vegetable matter consumed- Thus, in C. catla, which subsists on a predominantly crustacean diet, the ratio between length of fish and length of gut is 1:7, while in the case of C. mrigala, which consumes mainly plant matter and mud, the ratio is 1:11 (Mookerjee and Das, 1945). In fishes which change over from an initial carnivorous food habit to a predcaninantly herebivorous diet, the exact size at which this change over is effected can be determined indirectly from the ratio between the length of fish and length of gut. In L. gonius, when the fish is 6 to 10 mm in length, the ratio is 1:0.825 whereas at 11 to 20 and 21 to 30 mm length ranges it is 1:1.046 and 1:2.271 respectively. At initial stages the fish feeds mainly on zooplankton and when it gradually changes over to a diet consisting of fresh and decaying plant matter, detritus, phytoplankton organisms and mud, the length of the gut increases. In the adult stage the ratio is 1:10.442 (Table 2) and is thus comparable to that of C. mrigala.

Observations clearly indicated (Tables 3 and 4) that the growth rate and productivity of L. gonius, as compared to the major carps, is much less. In pond culture, fishes which have a high growth rate and food conversion ratio (like the major carps) are preferred for stocking, as they produce maximum fish flesh from the available food resources, and the uneconomical species, which compete for food v«th the cultivable ones, are avoided. From this stand-point, it is obvious that it will not be desirable to select L. gonius for culture, as the growth rate of the species is low and its food habits are incompatible with those of C. mrigala.

Periodical inspection of the fish markets at Sibsagar revealed that among the carps assembled, L. gonius is the most dominant, both by number and weight. The sources of fish supply include rivers, ponds, bheels and canals-No information is available at present on the percentage composition of L. gonius and other carps in the total fish landings from rivers and confined waters of Assam. However, a study for three years on the total catch and species and percentage composition of fishes from Nawpukri, a large tank which, as already stated, gets naturally stocked from the river every year during the floods (unpublished data), showed that, of the total carp species harvested, L. gonius constituted 25.22 to 54.24% by weight, thereby indicating that this fish is the most dominant species of carp in Assam waters. The hardy nature of the fish, its high fecundity and the abundance of its choiced food in the environment may be the main causative factors for the pre-eminent position of this species among the different carps in this State.

ACKNOWLEDGEMENTS

The authors wish to express their gratitude to Dr. V. G. Jhingran, Director, for his interest in the work.


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