Biology Reference
In-Depth Information
expression between the sexes. For instance, Small et al. (2009) have identifi ed
as many as 5,899 genes to express differently in males and females of
D.
rerio,
despite the apparent absence of heterogamety. Table 20 lists selected
examples of sex specifi c external secondary sexual characters. Hundreds of
similar examples may be recognized from a survey of any standard book
on 'Aquarium Fish'. These externally distinguishing characters are non-
invasive biomarkers, very much sought to quickly recognize sex in a given
commercially and biologically important fi sh. In sturgeons, the external
sexual dimorphism is less obvious. Vecsei et al. (2003) have found the shape
of external urinogenital opening of a live male is like the letter Y, while it
looks like 'O' in a female. Using this non-invasive criterion, sex of 82% of
live specimens can precisely be determined but not in dead specimens.
Another non-invasive technique employs Enzyme Immune Assay (EIA)
(i) to identify the mature female from the level of female-specifi c plasma
vitellogenin (Vtg) and (ii) to distinguish the immature female from the male
using plasma 17β estradiol and 11-KT levels in specimens of the giant air-
breathing Amazon fi sh
Arapaima gigus
. Adults are 100% accurately sexed
Table 20.
Selected examples of secondary sexual characteristics of fi sh
Characteristics
Remarks
Permanent
Sexual size dimorphism
Males > females
Macroandry, polygamous cichlids
Females > males
Microandry, poeciliids
Color
Male attractive,
Female attractive,
Red and yellow male morphs, purple-bellied female,
Pelvicachromis pulcher
Jaw
Male specifi c elongation in salmonids
Dorsal bend
Female specifi c in poeciliids
Barbel
Larger barbels in male e.g.
Loricaria parva
Pelvic fi n
Fused to form anal pouch in female
Corydoras aeneus
Dorsal fi n
Male specifi c
Betta splendens
Caudal fi n
Male specifi c
Betta splendens
Male specifi c elongated caudal sword,
Xiphophorus helleri
Anal fi n
Gonopodium in poeciliids
Gonadal papillae
Male specifi c in gobiids,
Symphodus
ocellatus
Gestation pouch
Male specifi c in syngnathids
Light organ system
Male specifi c in leiognathids,
Photoplagios rivulus
Transient
Ovipositor
Rhodeus sericeus, Pseudoblennius percoides
Color
R. sericeus,
male: olive emerald green on the back, orange-red on
throat and belly, bright red on dorsal and anal fi ns, and green on
caudal fi n; female: yellowish green
