Download Aquaculture: Genetics

Aquaculture:
Genetics
Dr. Craig Kasper
FAS 1012
Genetics: What is it?
• Genetics: The science of heredity and
variation.
• Heredity: transmission from generation to
generation (usually through the process of
reproduction) factors which cause the
offspring to resemble their parents (or not.)
Genetics Terms
• Selective breeding-the choosing of
individuals of a single strain and spp.
• Hybridization-the crossing of different spp.
• Crossbreeding-the mating of unrelated
strains of the same spp. to avoid
inbreeding
Selective Breeding
• “Artifical selection” as opposed to natural selection,
results in reducing genetic variability in a population.
Could be considered inbreeding if not closely monitored.
• If selective breeding involves excessive inbreeding
physical abnormalities, metabolic deficiencies, and
developmental abnormalities may occur.
• Inbreeding depression-loss of fitness due to inbreeding
– more likely to observe occurence of recessive traits
– Decrease in heterozygosity
Selective Breeding
• Although potential for deleterious results,
selective breeding rationalized by:
– size
– color
– shape
– better FCR
– reproductive capacity
– disease resistance
Hybridization
• Already looked at hybrid striped bass.
What other examples are out there??
Splake-brook trout/lake trout, Tiger Musky-northern pike/musky
Sunfish hybrids (many combinations)
• Hopefully achieve “hybrid vigor,” at least in
some trait.
• Most true hybrids are sterile, but not all.
Hormones in Aquaculture
• Hormonal cascade (see handout)
• Importance of Pituitary Gland
– Hypophysectomy removal of pituitary (under
isotonic growing conditions)
– Pituitary extracts used in some spawning
practices (carp)
Pituitary Gland - Master Gland
• Linked with hypothalamus of brain
• Produces hormones that affect other
endocrine tissues - indirect influence
• Produces hormones that
affect non-endocrine tissues
directly
Hormones
• Basic concept-a chemical messenger (intercellular)
released by endocrine glands.
Hormones in aquaculture
1) Human Chorionic Gonadotropin (HCG)
-induces ovulation
-injected IM (to get broodfish to synchronize
spawning),
Chorulon (FDA approved)
-dosage 50-2000 IU/kg wet weight for most fish
Others Hormones
2) Salmon Pituitary Extract (SPE)
-whole pituitary glands
-sold as a powder
-natural source of gonadotropins
3) Carp Pituitary Extract (CPE)
*Use extracts which are closest phylogenetically to fish
being injected!
Hormones
4) Leutinizing hormone-releasing hormone
=Gonodotropin Releasing Hormone
Leutizing Releasing horomone=GnRH
LHRHa=analog (synthetic) (potent)
-triggers pituitary to release gonadotropins
-Intraperitoneal injection (IP)-rapid absoption
Hormones
5) Methyltestosterone (MT)-used under strict control
-accelerates growth rate of some fish (no longer used for
this purpose)
-tilapia (when you need all male populations)
-sex reversal (apply during sexual differentiation
tilapia, walleye, yellow perch
-can be used to sterilize fish (monosex population)
-can be given orally (food)
6) Estradiol
-all female fish possible when used at the right time...
Gynogenesis
• Development of an ovum without fusion of
gametes
– usually haploid and die
– sometimes diploid larva develop
• requires retention of 2nd polar body during meiosis
• Amazon mollies, cruzian carp do this
• Induced by:
– radition, chemical, electrical currents, sperm
from related species
Sex reversal
• Genotypic females turned into phenotypic
males (MT)
– sex-reversed (XX) males cross with normal
females yields all female
• Polyploidy
– triploid fish (involves retention of 2nd polar
body, but fertilized by normal
sperm)....WHAT?!?
• essentially 2 sets of chromosomes from female,
one from male
Intersexed fish
• Hermaphrodites-contain ovotestes, can go
either way...
– MT treatment female after sex determination
occurs (ovary has already started to develop)
– intersexed fish must be killed to determine if
the process work! Not very good for
aquaculture?
Questions??