Pond Boss Forums STOCKING A NEW POND Types of fish to choose Female Bass stock for Ky pond

Bill,

LMB triploids have been demonstrated and tested. The results were not all that favorable for growth. In one study the triploids did grow longer over comparable periods of time but they were of less RW. IOWs they could put more energy in growing longer but the lack of growing gonadal weight caused them to be of lesser RW in the same water than the diploids. After reading this, I was less enthusiastic about triploidy as a means of inducing greater growth. I have come to consider that growth is primarily determined by consumption and what distinguishes fast growing fish is their tendency to eat more prey than their peers. I suspect growth hormone has a lot to do with a fish's consumption. Some have more and thus are inclined to consume more before feeling sated. With regards to the triploids in the study, one thing that was missing for triploids were the hormonal triggers that prompt them to consume in preparation for spawning. The reproduction investment is evidently financed by increased consumption. So the triploids were not doing this same increased consumption simultaneously. That said, the triploids probably had better FCR because none of their growth was being spent on gametes that are ultimately lost to the water when spawning. So triploidy may and probably would induce more efficient growth on the same ration. Triploidy, however, didn't seem to add any kind of increased relative consumption advantage. Also, inducing triploidy requires that all production be artificially spawned which is a disadvantage relative to spawning in ponds or raceways.

The most promising development recently, IMHO, is the discovery that female LMB are heterogametic. This means there are two chromosomes determining the females (YZ). If the egg is fertilized by irradiated sperm then the result is a haploid egg that will divide. If the first division is arrested (same procedure for producing triploids) the egg transforms to a diploid. The result of this will be the development of a normal male or a super female. A super female has two of the sex differentiating chromosome (ZZ) and when bred with a normal male (YY) the offspring are 100% female genotype (where the offspring were also 100% female phenotype in the limited sample of the study). The advantage is that a super female will breed naturally so these females could be used as brood stock that can reproduce in ponds and raceways using these standardized reproduction technologies. Hormone treatment can also produce phenotype males that are genetically (ZZ). Once phenotypic males (ZZ) are produced the production of super females and phenotypic males can be produced by normal spawning methods without any need for pressure treatments. All of these offspring will be ZZ and new males can be differentiated by hormone treatment during the sexual differentiation phase. Phenotypic ZZ males are useful for the production of super females broodstock as 100% of the offspring of these males are super female. Normal YY males would be preferred for the production of fry for the market place as the resultant offspring are 100% normal females when bred with super female.

There is quite a bit of work reaching a place where brood stock can be produced without artificial spawning but once there maintenance of lines is greatly simplified. This, however, may not take off due to a couple considerations related to food fish production. In particular, female LMB may not be as efficient at converting feed to filet and whole body weight. They grow more weight in eggs which are very energy dense and so a given weight of males might be grown on less feed than the same weight of females. Producing all female fry for grow outs could undermine the efficiency and profitability relative to mixed sex production. Gearing up for something like this probably would be limited to a single large producer that provides fry stock for growers serving recreational fisheries.

Possible caveat? Sometimes there is more to the differentiation of sex than the chromosomes. Some genes or gene combinations can influence the ultimate phenotype regardless of genotype. Temperature during sexual differentiation can also play a role. Bottom line? It may be possible (though not yet observed for LMB) that some genotypic females develop into phenotypic males under natural conditions.