Sex ratio of hillstream snow trout, Schizothorax plagiostomus Heckel (Teleostei, Cyprinidae) in the upland river Mandakini of Garhwal Himalaya

5 Pages·1997·2.9 MB·

by  N Singh

MISCELLANEOUS NOTES 417
SEX RATIO OF HILLSTREAM SNOW TROUT, SCHIZOTHORAX
27.
PLAGIOSTOMUS HECKEL (TELEOSTEI, CYPRINIDAE)
IN THE UPLAND RIVER MANDAKINI OF GARHWAL HIMALAYA
(With two text-figures
)
Sex ratio changes are used as an indicator Sample size, as expressed in percentage of total
of population behaviour, catch composition and catch during two years, does not indicate any
fecundity. Considering its importance, little relationship with sex ratio (Fig. 2).
information on this aspect is available for Indian S. plagiostomus breeds twice ayear, clearly
fishes (Pantulu 1961,Bhatt 1993,Nautiyal 1994). interceptedby well defined non-breeding season:-
The present study is an attempt to describe the first March, April and May, and second August,
sex ratio of an economically important and September and October. During the study period,
dominant snow trout species Schizothorax a consistent pattern of sex ratio change in
plagiostomus Heckel in relation to three water S. plagiostomus was observed. It was found as
parameters (total water discharge, water velocity 2.66:1 (January, February 1991), 2.29:1 (March,
and water temperature) of the glacier-fed upland April, May 1991), 2.24:1 (June, July 1991), and
river Mandakini in Chamoli dist. of Garhwal the lowest value of one breeding cycle 2.03:1
Himalaya, Uttar Pradesh. (August, September, October 1991; second
Adult S. plagiostomus were collected from breedingseason). Itagain rose to2.90:1 (November,
the glacier-fed high altitude Mandakini river, December 1991, January, February 1992), 2.28:1
covering a stretch of about 30 km (Fig. 1). (March, April, May 1992; first breeding season),
Specimens were randomly sampled every month 2.16:1 (June,July 1992), andagainthelowest 1.59:1
fromJanuary 1991 toDecember 1992 at four sites (August, September, October; second breeding
- Bheri (1020 m), Chandrapuri (827 m), season) followed by an abrupt rise 2.35:1
Agustmuni (760 m) and Tilwara (724 m). In view (November, December 1992). It is, therefore,
of its breeding twice a year, catch data of evidentthatmalespredominatetheadultpopulation
S. plagiostomus had been computed in terms of of S. plagiostomus. The sex ratio remains higher
sex, breeding and non-breeding season. The during the first breeding season (March, April and
numerical figures of males and females, during May) and lowest during second breeding season
breeding and non-breeding season, arefirstpooled (August, September and October) (Fig. 2).
together and then separately expressed as a The water condition parameters have their
percentage of the total catch of each year. The own bearing on the sex composition of
M
ratio of : F (M - number of males, and F - S. plagiostomus. Adult males comprised the
number of females) during different seasons lowest sex ratio when monthly mean values of
denotes the corresponding sex ratio. water parameters were at their peak - total water
m
The water condition parameters of river discharge (155.34 3/sec., 170.63m3/sec.), water
Mandakini, viz., total water discharge (m3/ sec), velocity (1.805m/sec., 1.919m/sec.) and water
water velocity (m/sec) and water temperature temperature (15.05°C, 15.8°C) during second
(0°C), during corresponding study period, breeding season (August, September, October
obtained fromU.P. IrrigationDepartmentSrinagar 1991 and 1992 respectively). Higher values of
Garhwal (as measured at Chandrapuri, Fig. 1), sex ratio were found during firstbreeding season
were converted into mean monthly values for the (March, April, May 1991 and 1992 respectively)
corresponding seasons. when mean monthly values of water condition
We studied 4601 adults (3110 males and parameters of river Mandakini just commenced
1491 females) caught at four sampling sites. a rising trend from the lowest monthly mean
418 JOURNAL BOMBAYNATURAL HIST SOCIETY Vol. 94 (1997)
"\
uttarkash
(. LOCATION IN INDIA
0 50
it I K«n
Fig. 1. Location of the sampling sites on the river Mandakini
MISCELLANEOUS NOTES 419
FMAMJJ ASON FMAMJJASOND
DJ
J
Fig. 2. Sex ratio of Schizothoraxplagiostomus in relation to sample size (male and female numbers pooled
&
and separately) and water parameters (total discharge, velocity temperature) during breeding and
non-breeding seasons for 1991, 1992 (in the river Mandakini)
420 JOURNAL, BOMBAYNATURAL HIST SOCIETY, Vol. 94 (1997)
values during extreme winters. Thus, sex ratio follow a consistent pattern, i.e. higher during the
in S. plagiostomus somehow has an inverse first breeding season when values of aquatic
relationship with the values of water parameters. parameters of river Mandakini just begin to rise
from the lowest values of extreme winter, and
Discussion
lowest sex ratio during second breeding season
Nikolskii (1980) mentioned that optimum when values ofwaterparameters would beattheir
sex ratio in nature is close to 1:1 in adult part of peak. It may be presumed that, starting from late
the population but it may be far from this in February onwards, the potential sexually mature
particular age and size groups; males usually brooders begin upstream pre-spawning migration
predominate in younger groups because they tend from lower stretches of larger glacier-fed rivers
to mature earlier and live less longer. Thus, (like Ganga, Alaknanda etc.) to their smaller
optimumsex ratio may varydrastically as aresult glacier-fed tributaries (like the Mandakini) in the
of being affected by numerous factors. upperreaches. Whiledoing so, the males lead this
Sex composition and sex ratio of fish upstream migration, followed by females. Earlier
population have been investigated in a number arrival of male brooders changes the sex ratio
ofEuropean fishes, viz., Husodauricus (Soldatov drastically in local populations at a particular
1915), North Caspian roaches (Monastyrskii spawning/breeding locality. The first breeding
1940,Leuciscus idus (Soloveva 1960), coal fishes season is followed by the non-breeding period
(Mironova 1961), sea perch (Freund 1961), (June, July). From July onwards, the upstream
coregonids (Titova 1962), roaches and carp beams migration of potential and/or rest of brooders,
(Demin 1962) to mention a few. However, the especially to smaller spring-glacier fed tributaries,
pattern of variation in the sex ratio is not commences again which further alters thesexratio
generalised because no single factor accounts for to its lowest values during the second breeding
such a change in all classes. Different factors season (August, September, October). It is
cause the sex ratio to change in different cases. possibly because an earlier departure of males
Females predominate in fishes of low fecundity from potential spawning/breeding sites has
such as Pomatoschistus caucasicus where the already started. This is the time when values of
male is larger than the femalebut males are fewer aquatic parameters touch their zenith. The
in number (Koblitskaya 1961). Females also breeding process of one year smoothly passes
predominate in many other cases where a male through to the next year, thus maintaining and
produces several batches of sperms but female repeating the periodicity of the process.
produces only one batch of ova. Conversely, in Higher sex ratio during the first breeding
other cases, males predominate, e.g., Platessa season may result from (1) late arrival of females
platessa(Wimpenny 1953),Pseudoscianacorcea and early arrival of males, (2) fresh recruitment
(Chen Ju Fen 1962). Again, in many cases, of new batches of subadults into male brooders,
different population of species residing in (3) difficulties encountered by female brooders
different regions exhibit different sex ratio, e.g. during upstream migration because of their full
Carassius auratus gibelio in Chinese and grown belly, and lower water discharge of the
Japanese waters has a ratio of 1:1 but in Amur river. Otherwise the conditions are conducive for
river the ratio is 0.48:1 (Nikolskii 1956). spawning and breeding as a result of rising
In the present investigations, the sex ratio temperature and moderate water velocity, and
of S. plagiostomus was never close to the (4) vulnerability offemales to their predators and
optimum 1:1 during either breeding or non- other natural hazards. Possibly, environmental
breeding season. Males predominate throughout conditions during the firstbreeding season favour
the year. The changes in the sex ratio seem to the male part of the population while females are
,
MISCELLANEOUS NOTES
421
favoured during second breeding season. Acknowledgement
Nautiyal (1994) found that alteration in the
sex ratio ofTortoris initiated by thepre-spawning I am grateful to Professor Asha Saklani,
migratory phase itself in the brooder population Head, ZoologyDepartmentforresearch facilities.
only. Moreover, at a particular spawning site, the Financial assistanceprovidedby theGovernment
&
brooder males tend to be in surplus number and of India, Ministry of Environment, Forests
New
stay longer; the brooder females tend to leave the Wildlife, Delhi is thankfully acknowledged.
spawning site soon after spawning. This causes a
change in the sex ratio which has its own adaptive October 22, 1996 N. SINGH
significance for the control mechanism of Zoology Department
reproduction and sex composition ofareproducing P.O. Box 83,
population (Nikolskii 1980). More information on HNB Garhwal University,
sexratio andsex composition ofpopulation-related Srinagar Garhwal 246 174,
species of schizothoracids from other hillstreams U.P, India
.
would present a total picture.
References
Bhatt, K.C. (1993): Present status and olfaction ofsnow *Nikolskii, G.V. (1956): ‘Fishes of Amur Basin’. Izd.
trout in the river Mandakini (Garhwal Himalaya). Akad. Nauk. SSSR. (in Russian).
Ph.D. thesis, HNB Garhwal University, Srinagar Nikolskii, G.V. (1980): ‘Theory of Fish Population
Garhwal (U.P., India). Dynamics. (Translated by J.E.S. Bradley) (R. Jones
Chen-Ju-Fen (1962): Breeding grounds ofPseudosciana ed.), Bishen Singh MahendraPal Singh, Dehradun &
corcea Rich, near the Sunchou coast, Kwangtung Otto Koeltz Science Publishers, Koeninstein,
Province. 7th MeetingoftheCommissiononFisheries Germany.
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Demin, D.Z. (1962): Semimigrant fish ofthe delta ofthe of Mystus gulio Ham. by the use of pectoral spines
Terek. Vopr. Ikthiol, 2(1): 22. with observation on its biology and fisheries in the
Freund, K. (1961): Some observation on the redfish of Hooghly estuary. Proc. Nat. Inst. India Sen B27: 4.
A
theLabradorregion.Rapp, etProces-Verbaux,Conseil Soldatov, V.K. (1915): survey of researches on the
Perm Intemat. Explor. Mer. pp 150. Amur in 1909-13. Part 2. The Amur sturgeon. ‘Data
Koblitskaya, A.F. (1961): New data on the biology of on Russian Fisheries’, 3rd Issue, St. Petersburg,
Pomatoshistus caucasicus Kaw. ofthe outer delta of pp. 12.
the Volga. Vopr Ikthiol. 1: 19. Soloveva, N.S. (1960): Fish and fisheries of
Mironova, N.V. (1961): Migration and causes of LakeCherdynskii, Perm region. Uch. Zap. Perm Univ.
variabilityinimmaturecod.TrudyMurmansk. Morsk. 13: 1.
Biol. Inst. 3: 7. Titova, V.F. (1962): Breeding of Lake Coregonus
Monastyrskh, G.N. (1940): Methods of evaluating the lavaretus L. Trudy Karel. Fil. Akad. Nauk SSSR,
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pp. 11. Wimpenny, R.S. (1953): ‘The Plaice’. Cambridge
Nautiyal,P. (1994):Riverinemahseer. In ‘Mahseer-The University Press, London.
Game Fish’ Rachna Publishers, Srinagar Garhwal, * Not referred to in original.
pp B23.
28. ON THE SPECIFIC IDENTITY OF OMPOK BIMACULATUS
(SILURIFORMES SILURIDAE)
:
(With one plate)
The genus Ompok Lacepede is currently viz. O. bimaculatus (Bloch), O. malabaricus
represented by four species in the Indian region (Val.), O. pabda (Ham. Buch.) andO. pabo(Ham.