Guppies are small freshwater fish often used as model organisms in studies of ecology, evolution, and behavior. They display sexual dimorphism, with males having colorful spots and larger fins compared to the duller females. Females mate with multiple males. Goldfish are social fish that live in groups and have strong learning abilities. They also display sexual dimorphism, with females being larger and rounder than males, who have distinctive breeding features. Swordtail fish similarly show sexual dimorphism, with colorful male swords and fan-shaped female fins for breeding purposes.

3. Guppies
Guppies (Poecilia reticulata)

5. Guppies are used as a model organism in the
fields of ecology, evolution, and behavioural
studies.
 Guppies have 23 pairs of chromosomes, including
one pair of sex chromosomes, the same number
as humans.
The guppies were expected to eat the mosquito
larvae and help slow the spread of malaria.
Guppies are ovoviviparous.

6.  Sexual dimorphism in Guppies :
Guppy exhibits sexual dimorphism, a phenomena that the
two sexes of the same species exhibit different
characteristics beyond the differences in their sexual
organs, in the body size and shape, and colour patterns.
Males have colourful spots and ornamentations while
females are generally grey in colour. Males have large
fins. Females are larger than males.
Guppies have the mating system called polyandry, where
females mate with multiple males.

9. This species is a very successful aquarium fish. There
are 12 varieties of Mollies, each with distinguishing
characteristics and traits.
Some of them are known as Black sailfin molly. Pointed
mouth molly, Short finned molly, Ghost pearl molly,Gold
dust molly, Balloon molly Red sunset molly.
The body is oblong with a round caudal peduncle and a
small dorso-ventrally flattened head with protruding
jaws .

10.  Sexual dimorphism:
 Poecilia sphenops displays sexual dimorphism
whereby males are smaller (8cm compared to
12cm of females) and more colourful, particularly
males’ larger caudal fins.
Males use the colourful dorsal and caudal fins as
secondary sexual features to attract female mate.
Female Poecilia sphenops have a dark patch that
appears between the abdomen and the anal fin
(gravid spot).

11. Sword tail (Xiphophorous hellerii

13. Xiphophorus hellerii is a common laboratory
animal and has been used as a model organism
The fish body is elongated and flatted from
sides. The feature of the fish is its unusual tail in
a shape of sword, which actually gave the name
to it. The tail may be either rounded with one ray
or it may have several rays.
Swordtail fish lifespan is about 3-5 years.
Swordtail is quite a large fish.

14. Sexual dimorphism in swordtail fish is
moderate, with the female being larger than the
male, but lacking the ‘sword’. Only the male has
the "sword" extension on the bottom of the tail
fin. The male is also slimmer and has a "sword"
shaped anal fin called a gonopodium.
The female has a fan shaped anal fin, is rounder
of body, and will have a spawning patch at
breeding time.

15. Goldfish (Carassius auratus

17. Common goldfish are social animals who prefer living in
groups. They are able to interact with any fish belonging to
the same species.
Goldfish have strong associative learning
abilities, as well as social learning skills.
Goldfish have one of the most studied senses of vision in
fish. Goldfish have four kinds of cone cells, which are
respectively sensitive to different colours: red, green, blue
and ultraviolet.
The ability to distinguish between four different primary
colours classifies them as tetrachromats.

18. Goldfish are gregarious,
displaying schooling behaviour, as well as
displaying the same types of feeding behaviours.
Goldfish-specific food has less protein and more
carbohydrate than conventional fish food.

19. Sexual Dimorphism/Gender Differences:
The female varieties tend to be slightly more
rotund than males, and just bigger in general.
Male vents are long and often have a triangular
outline.
A male goldfish has a "midline ridge," or a raised
line that extends from the back of the pelvic fins
to the vent.
Male goldfish develop small white spots on their
gill-shields, known as breeding tubercles