Aquaculture: Genetics Dr. Craig Kasper FAS 1012

Genetics: What is it? Genetics: The science of heredity and variation. 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.)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.Selective breeding-the choosing of individuals of a single strain and spp. Hybridization-the crossing of different spp.Hybridization-the crossing of different spp. Crossbreeding-the mating of unrelated strains of the same spp. to avoid inbreedingCrossbreeding-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.“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.If selective breeding involves excessive inbreeding physical abnormalities, metabolic deficiencies, and developmental abnormalities may occur. Inbreeding depression-loss of fitness due to inbreedingInbreeding 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: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.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.Hopefully achieve “hybrid vigor,” at least in some trait. Most true hybrids are sterile, but not all.Most true hybrids are sterile, but not all.

Hormones in Aquaculture Hormonal cascade (see handout)Hormonal cascade (see handout) Importance of Pituitary GlandImportance 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 brainLinked with hypothalamus of brain Produces hormones that affect other endocrine tissues - indirect influenceProduces hormones that affect other endocrine tissues - indirect influence Produces hormones thatProduces hormones that affect non-endocrine tissues affect non-endocrine tissues directly directly

Hormones Basic concept-a chemical messenger (intercellular) released by endocrine glands.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 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... -all female fish possible when used at the right time...

Gynogenesis Development of an ovum without fusion of gametesDevelopment of an ovum without fusion of gametes –usually haploid and die –sometimes diploid larva develop requires retention of 2 nd polar body during meiosisrequires retention of 2 nd polar body during meiosis Amazon mollies, cruzian carp do thisAmazon mollies, cruzian carp do this Induced by:Induced by: –radition, chemical, electrical currents, sperm from related species

Sex reversal Genotypic females turned into phenotypic males (MT)Genotypic females turned into phenotypic males (MT) –sex-reversed (XX) males cross with normal females yields all female PolyploidyPolyploidy –triploid fish (involves retention of 2 nd polar body, but fertilized by normal sperm)....WHAT?!? essentially 2 sets of chromosomes from female, one from maleessentially 2 sets of chromosomes from female, one from male

Intersexed fish Hermaphrodites-contain ovotestes, can go either way...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??