What treatment would you use for hormonal sex reversal? What are the problems with this method?
Methyl Testosterone - only in food
- poor market acceptance
- must treat all production fish
- obtain fry less than 10 days from hatch
what are the four ways of controlling reproduction?
- monosex culture
- early cropping of single year class
- predator stocking
- cage culture
What are the 6 methods of creating a monosex culture?
what is the desired result?
-manual sexing
-hybrids
-hormonal sex reversal
-GMT tilapia
-triploids
-high temperature incubation
» all boys no girls «
5 ways to sex an oreochromis
- males longer pointed dorsal and anal fins
- more developed jaws in males
- color at breeding
- males larger
- location of urogenital openings
what are the 3 advantages of hybrids?
- do not treat all production fish
- less expensive (labor, material)
- better market
problems for triploiding tilapia
- females still in stock - slow growers
- must shock minutes post fertilization
- hand stripping
- apply heat shock from 27* to 42*C post fertilization for 3 minutes
- causes high mortalities
what is the trade name of YY supermales?
GMT -
genetically male tilapia
guarunteed male tilapia
2 methods of creating GMT. what percentage of monomales do you wind up with?
i) androgenesis: 1/2 yy 1/2 xx
ii) hormonal monosexing: 1/4xx 1/2 xy 1/4yy
list one observation which could be made microscopically that would indicate a newly developing oocyte has entered prophase 1 of meiosis
presence of lipid droplets
Name 2 chromosome manipulation techniques which require application o pressure or temperature shock to suppress the first cleavage division of embryonic development
gynogenesis
androgenesis
tetraploids
twice during oogenesis, meiosis stops while other developments occur. what two events trigger the resumption of meiosis after these arrests?
vitelogenesis finished, fertilization
what is the main reason for producing tetraploid fish?
to create triploid in the future
what two fish organs are responsible for synthesis of the phospholipoprotein referred to as vitellogenesis?
liver, gonads
at any temperature, why does oogenesis take longer in large fish eggs compared to small eggs?
larger eggs = more time of deposition of the yolk in eggs
what would you observe in the ovary of a fish that displays asynchronous oogenesis?
eggs at all different stages of development
what hormone serves fish as the gonadotropic hormone releasing hormone inhibitory factor?
dopamine
what chemical can be used to competitively bind to estrogen receptors, to eliminate estrogen’s negative feedback on recrudescence, when inducing spawning in fish?
tomoxfine
what is the main environmental cue that triggers recrudescence in temperate zone fish?
photoperiod
what organ secretes melatonin?
pineal gland
name two compounds which can be combined with reproductive hormones to produce a slow release, injectable pellet for induction of recrudescence in fish?
cellulose, coconut oil, polymers, cholesterol
when during oogenesis are circulating gonadotropin concentrations higher in fish?
just before ovulation
pelagophiles scatter non-adhesive eggs in open water. what characteristic of the egg controls their density and determines their depth of incubation?
oil content
give an example of an auxilary respiratory structure that might be found on a larval fish from a low oxygen environment?
external gills, fin folds
what environmental incubation problem is overcome by the many species of fish which build bubble nests?
low O2
