IN FISH CHROMOSOMES
Amita Saxena and
Fisheries, Gbpuat, Pantnagar 263145, India
chromosomes are responsible for the mechanism of inheritance to
express the genetic characteristics in successive generations. In
1902, W. S. Sutton state hypothesis that the chromosome provide the
physical basis of heredity. Chromosomes are named from the fact that
they stained preferentially with certain dyes and show suitable
cellular material prepared for microscopic examination. They appear
thread like at certain times and are composed of linear complexes of
deoxyribonucleic acid (DNA), genetic material proper and histone
proteins which have a supporting or structural role. All living
organisms have chromosomes. Prokaryotes (bacteria and virus) are
different from eukaryotes (plants and animals). The eukaryotic cell
has nucleus that carries chromosome complements. The number of
chromosomes per cell is the characteristics of the particular species
but in case of fishes these chromosome numbers different within same
species also observed. These chromosome numbers made up of maternal
and paternal origin of two sets so called as diploid. Single set (egg
or sperm) of chromosomes called as haploid. The chromosomes numbers
varies in fishes.
chromosome material is called chromatin which is of two types like
euchromatin and heterochromatin. The euchromatin stains lightly and
heterochromatin stains darkly. Euchromatin contains genes in a linear
array like beds on a string and heterochromatin is genetically inert
and acting in maintaining structural integrity of chromosomes and
regulation of the gene expression. Heterochromatin made of highly
repeated simple sequences of DNA. The part of chromosome at the end
called telomere and the constriction called centromere. The telomeres
are stable entities essential for maintaining the integrity of
chromosome threads. The centromere controls the movement of
chromosomes during cell division. Both the telomere and centromere
are located in the heterochromatin. The chromosomes again divided as
metacentric, telocentric and acrocentric based on the position of
centromere in the chromosome. When centromere located at center, then
it is called as metacentric, at or very near to one end called
telocentric and acrocentric having one arm very longer than other.
Intermediate cases are described by using the prefix ‘sub’. The
fish chromosomes are comparatively small in size and have its own
characterisrics. The NF value i. e. 'nombre fundamental' or
number of chromosome arms is important because it gives the genetic
content of a chromosome complement.
chromosome staining is achieved by using dyes having affinity for
DNA. But the different chromosome banding techniques shows the finer
structure of chromosomes.
The importance of
fish taxonomy is not only with description of new forms, but also
with placing each form within taxonomic system that shows it’s
relationships to other forms .For more than a century, systematists
have sought to organize this diversity by studying aspects of their
external and internal morphology which have been especially
successful in defining species and in organizing these species into
genera. These groupings have usually been confirmed when examined
with cytogenetically approaches.
In the last
few decades works have been focused on the field of cytogenetic
investigation of fishes, especially in the area of systematics,
mutagenesis and aquaculture. The karyotype is the chromosome
complement of an individual or related group of individuals, as
defined by chromosome size, morphology and number. Though for all
somatic cells of all individuals of species, the number of
chromosomes is used as an indicator of classification of species of
chromosomes and interrelationships within families. The studies of
these characters help to investigate the aquatic structure for the
investigate the aquatic structure for the population of each species
population in each habitat, so it can determine what species
are related to each other in an accurate manner?. This may help to
facilitate the hybridization between them in the future to improve
studies on fish have been useful to provide information concerning
evolutionary and taxonomic studies, as well as for the genetic
improvement of commercial fish stocks (Gold,
1979). Several techniques have been devised to obtain mitotic
chromosomes in fish, ranging from direct preparations to long-term
cell culture (Denton,
1982 and Alvarez
et al., 1991, among others). Among these methodologies, in vivo
procedures, usually time- and cost-saving, have been the most
1974 and Rivlin
et al., 1985). However, to perform direct techniques, it is
necessary to carry out a previous colchicine treatment of live
animals for about 1 h. Very often, this is a not a feasible
method, as in the case of delicate/fragile species after lengthy
transportation or species requiring specially suited tanks (e.g.,
marine species). Consequently, most of the available cellular
material can be lost (Ozouf-Costaz
and Foresti, 1992 and Maddock
and Schwartz, 1996).
chromosomes consist of a single
molecule of DNA
to visual proof]
many copies of 5
kinds of histones.
Histones are proteins rich in lysine
residues and thus positively-charged. For this reason they bind
tightly to the negatively-charged phosphates
a small number of
copies of many different kinds of non-histone proteins. Most of
these are transcription
that regulate which parts of the DNA will be transcribed
have been the subject of an increasing
number of cytogenetic investigations in the areas of systematics,
mutagenesis and aquaculture. From about 20,000 - 40,000 fish species
estimated to occur on this globe, the basic karyotypic
characteristics[i.e., diploid chromosome number (2n) and number of
chromosome arms (NF) are known for not more than 1700 species, which
represent only about 9% of the total number of species available.
Efforts have been made from time to time to update the karyotype
list of available species.
is a teleostean species having a tetraploid origin. Inspite of the
fact that carp possesses a large number of very small chromosomes, it
has been fairly well studied by the cytogenetic researchers. In a
majority of these studies, a diploid chromosome number has been
reported to be 2n = 100 in common carp (Raicu et
1972; Denton, 1973; Zan & Song, 1980; Blaxhall, 1983; Labat et
1989; Larka & Rishi, 1991; Anjum & Jankun, 1994; Anjum,
1995). Diploid chromosome number of native carp from Amur river has
been divided into eight well-defined groups on the basis of their
morphology and a standard karyotype has also been proposed (Rab et
1989). C-banding and Silver-NOR staining has also been employed in
some cytogenetic studies on common carp (Takai & Ojima, 1982;
1985; Sola et
present a high chromosome diversity showing
diploid number variation range, including different
of ploidies, sex chromosomes, chromosome supernumeraries,
several cases of polymorphisms, related particularly to
and NOR sites. Two main general trends of chromosome
can be observed among neotropical fishes.
several fish groups show a chromosome evolution relatively
from the point of view of the karyotypic
Sister species show conspicuous differences in
structure and most often also in the number of chromosomes.
On the other hand,
there are fish groups in which
evolution has been shown to be less divergent, and
this case whole families or even groups of families may share a
karyotype structure and equal number of chromosomes.
fish groups appear conservative also with respect to the
bearing chromosomes. In this case, NOR chromosome location
invariable among species. In contrast, several other
present wide NOR variability. Sister species may show
diverse chromosomes bearing nucleolar organizing regions.
NOR and heterochromatin relationship is also very diverse
fishes and this may indicate organizational differences involving
chromosome segments. Thus, neotropical fish fauna
great chromosome variability, verifiable also by NOR
The karyotypes of
five species of Scorpaenidae (genera Scorpenopsis,
the Indian Ocean are characterized
a diploid set of 48 chromosomes (mainly acrocentric
subtelocentric) and by a NOR location on the small arm of
medium-sized pair. All the chromosomes stained uniformly with
whereas C-banding evidenced a small amount of heterochromatin.
the marked morphological differences
these species, the low degree of diversification of the
with respect to the ancestral set of teleosts
= 48 acrocentric chromosomes) suggests that chromosome
has not undergone profound rearrangements during
evolution of these taxa.
(chromosome no. structure, definitions of diff. types, diversity,
manipulation, importance added)?
cytogenetics studies of crustaceans are relatively few and very
difficult to perform because their chromosome numbers are large
2003, Lee et
2004), chromosomes are small and theirs shapes are very variable
including metacentric, submetacentric, and acrocentric chromosomes
2004). Marine crustaceans such as the white shrimp Litopenaeus
(Dumas & Campos-Ramos 1999) and the Chinese shrimp Fenneropenaeus
2003), as well as in marine bivalves such as the Japanese oyster
1989) were studied to get good results for manipulation of
chromosomes. Consequently, information on the basic genetics of the
tropical crayfish P.
is necessary not only to reinforce its potential for aquaculture, but
also for genetic improvements and conservation.
Loricariidae is one
of the largest fish families of the world, with about 650 species
separated into six subfamilies. To date, cytogenetic data on only 56
species of this family are available. The lowest diploid number,
was observed in Ancistrus
1 (Ancistrinae) and the highest diploid number, 2n=70,
was observed in Rineloricarian
sp. (Loricariinae). The nucleolar organizer regions (NORs) were seen
at a terminal position in six species and at an interstitial position
in two. The karyotypic analysis of Loricariinae and Ancistrinae
species revealed that these groups exhibit a large diversity of
diploid numbers, suggesting the occurrence of intense karyotypic
evolution during their evolutionary history.
Reis et al. (2003) consider the Loricariidae as the largest family of
catfishes in the world, little is known about the karyotypic
organization in this group (Artoni and Bertollo, 2001).
Meanwhile, some studies provide some cytogenetics information for
Loricariinae (Scavone and Júlio Jr., 1994; Giuliano-Caetano, 1998;
Artoni and Bertollo, 2001), Hypoptopomatinae (Andreata et al.,
1992, 1993, 1994), Hypostominae (Artoni et al., 1998, 1999; Artoni
and Bertollo, 1996, 1999, 2001; Alves et al., 2006), Ancistrini
(Lara, 1998; Artoni and Bertollo, 2001) and Neoplecostominae (Alves,
2000; Kavalco et al., 2005).
spite of the small amount of information compared with the number of
the species already described for Loricariidae, the available data
demonstrate that this is a group of great interest for cytogenetic
studies, due not only to the variation in chromosome number, 2n = 36
in Rineloricaria latirostris
(Giuliano-Caetano, 1998) to 2n = 96
in Upsilodus sp
(Kavalco et al., 2005), but also to the occurrence of many
chromosomal rearrangements, suggesting a divergent karyotypic
evolution (Artoni and Bertollo, 2001).
is considered to be one of the most
diversified groups of Neotropical fishes, and is one of the most
studied genera from a cytogenetic point of view, showing a variation
in chromosome number from 2n = 54 in H.
plecostomus (Muramoto et al., 1968,
in Artoni and Bertollo, 2001) to 2n = 80 in Hypostomus
sp E (Artoni and Bertollo, 1999).
The family Gobiidae
is quite interesting because of its controversial morphological
(Fage, 1925; Arai and Sawada, 1974; Nishikawa et al., 1974) and its
evolutionary stage which is not completely known.
A high variability of chromosome
number occurs within this group ranging from 2n = 40 to 2n = 62
still is no agreement as to the number of chromosomes characterizing
2n = 45 was
proposed for a female specimen
in the Thyrrhenian Sea (Cataudella et a!., 1973), n = 25 and 2n = 50
specimens caught in the Northern Adriatic Sea (Colombera and Rasotto,
= 46 for eight male and female specimens caught in the Southern
near Spanish coasts (Thode et al., 1983).
et aL, (1983) claim that Gobius
is characterized by male heterogamety (XY). The occurrence of a large
metacentric chromosome in the female
investigated by Cataudella et al. (1973) does not agree with the
determination proposed for this species.
(snappers) is a group composed of 17 genera
and 105 species of mostly reef-associated
marine fishes, which are distributed in all the tropical and
subtropical seas of the world (Nelson, 2006). The family is divided
in four subfamilies. Three smaller subfamilies include the
Paradichthyinae, with two monotypic genera (Symphorus
the Etelinae, with five genera (Aphareus,
Aprion, Etelis, Pristipomoides and
and 19 species, and the Apsilinae, with four genera (Apsilus,
Lipocheilus, Paracesio and
and 12 species (Nelson, 2006). The subfamily Lutjaninae is the
largest, with three monotypic genera (Hoplopagrus,
the genera Macolor
two species each, and the genus Lutjanus,
which is the most speciose, with 64 species. In Venezuela, Cervigón
(1993) recognizes six genera of Lutjanidae (Etelis,
Pristipomoides, Apsilus, Ocyurus, Rhomboplites
) including 15 species, 10 of which belong to the genus Lutjanus
analis, L. apodus, L. aya, L. bucanella, L. cyanopterus, L. griseus,
L. jocu, L. mahogoni, L. purpureus, L. synagris
In spite of their
high number and their ecological and economic importance, cytogenetic
studies on Lutjanidae are scarce. In fact, among the 105 recognized
species of Lutjanidae, barely five species have been karyotyped to
& Prasad, 1980), L.
1979; Ueno & Takai, 2008), L.
(Ueno & Ojima 1992), and L.
(Ueno & Takai, 2008). For most of them, only the chromosome
number and morphology have been reported and there is no data
regarding the chromosomal distribution and composition of the
constitutive heterochromatin or numbers and locations of the major
and minor ribosomal genes, which have proved to be useful markers in
the investigation of the phylogenetic relationships among fish
species within a family (Sola et
on the chromosomes of fishes have not been successful or widespread
as in other vertebrate groups. Fish karyotypes are generally
characterized by a large number of small chromosomes, discouraging
researchers from pursuing fish-karyotype analysis. Therefore
karyological data on fish are available only for a small percentage
(about 10%) of some 25 000 species taxonomically known so far. The
Bagridae family of fish is the richest and most important of the
teleostei class and its members are distributed throughout the
In the Bagridae family, the fish Mystus
(Smith, 1945) is economically important and distributed in the
semitemporal freshwater system of south India. Based upon the fish
chromosome data, it seems that the chromosome number depends on the
species in the Bagridae family, suggesting some major chromosome
rearrangements which might have played a significant role during
speciation and evolution of Bagridae. The family of Bagridae has
received special attention in Asia; up to 40 species have been
karyotyped so far. The fishes belonging to family Bagaridae have good
nutritive value and a candidate species for aquaculture. The number
of chromosomes varies between species in genus, Mystus.
the diploid chromosome number has been reported to be 2n = 586.
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