Something to think about... part 1: even sex ratios

Discussion in 'CBP questions and answers' started by tjudy, Feb 8, 2013.

  1. tjudy

    tjudy Executive Board Staff Member

    One of the projects I have been working on is a program that looks at the way the hobby handles conservation priority species, and asks the tough questions about whether we are handling them correctly or not. I am most concerned with the need to preserve the genetic resource in a species. My research landed me ultimately within the aquaculture science industry, where researches are light years ahead of the aquarium hobby when it comes to breeding fish and getting the most benefit out of limited breeding stocks.

    There are a LOT of things to take a hard look at, and I want to have these discussions in our club. I am going to start one of these 'something to think about' threads periodically with one of the changes that I believe needs to happen in the hobby. Some of them will overlap. Some will make immediate sense. Others take some effort to wrap your head around. Some are easy changes, and others will make you question the validity of hobby conservation at all. But they are things we need to look at, as fish breeders, if we are serious about species maintenance.

    Topic 1: Breeding with even sex ratios

    There is a tool in aquaculture known as the 'effective breeding number' (N), which is a calculation that predicts the number of fish in a breeding population that are actually useful. The only fish that count in the number are the males and females that actually produce fry. The larger the N value the better to prevent a bad situation called genetic erosion. Lots of things go into genetic erosion (inbreeding being a big reason), but that is a discussion for another thread. It is hard to put a calculation in this forum, so I will spell it out:

    Effective Breeding Number (N) =

    4(# males)(# females)
    (# males) + (# females)

    In this calculation only the males and females that produce fry count. The highest the N value can be is the total number of fish in the population, and it will only get to be that large if the sex ratio is even.

    Example 1: Uneven sex ratio 2 males 10 females (like a colony of cichlids)

    4(2 males)(10 females)
    (2 males) + (10 females)

    80 / 12 = 6.67

    This means that even though there are 12 fish in the breeding pool, the effect on the genetic health of the population is as if there were only 6 or 7 fish in the breeding pool. This is because half of the genes in the offspring are only coming from two fish.

    Example 2: even sex ratio 10 males 10 females

    10 + 10

    400 / 20 = 20

    So when the sex ratios are even the effective breeding number goes up to the actual population.

    OK... this is an ideal situation where all of the fish are spawning. This may work with livebearers, cory cats, danios and other fish that do not get dominant males that kill each other... but in even sex ratios in mbuna tank will not result in all the fish breeding. Only the dominant males will spawn. Or is that really true? Maybe so in a 55 gallon tank, but the opposite has been demonstrated in aquaculture.

    Take a population of 100 Psuedotropheus demasoni, with an even sex ratio (50 of each), put them in a 2000 gallon pond or vat and watch what happens. Given the space and numbers, dominance changes. A male that is breeding today may not be breeding tomorrow. Ten males may have breeding stations set up all at the same time, and a breeding female may spawn with more than one of them in a single session... literally laying ten eggs with one male, five with another, ten more with a third and so on until she is done.

    Can this dynamic even be attempted in an aquarium situation? Is there a way to create a breeding population of, for example, 20 fish in an even sex ratio with all ten males bringing sperm to the party? I know there is a way. More than one... but let's see what we can come up with as a group.
    Cinnamonsticks likes this.
  2. bahamafj11

    bahamafj11 Well-Known Member

    Hate to state the obvious, but........................

    FLOOD THE BASEMENT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  3. Dusty

    Dusty Well-Known Member

    10 tanks,10 pairs, rotate!

    Witamygreatdanes and tjudy like this.
  4. tjudy

    tjudy Executive Board Staff Member

    That works well, even for species that are colony spawners. Another option is big colonies of females and rotate 2-3 males in. One way to ensure all the females are breeding is to remove them to a new colony tank after they have spawned (and you have collected the fry). Once the female colony is back up to the number of females you want, add different males in with them.
  5. Marine590622

    Marine590622 Advisory Board Staff Member

    So I should be looking to trade males on my care species to improve genetics?
  6. tjudy

    tjudy Executive Board Staff Member

    That is also a good option Randy, especially if we start looking at (for example) all of the Xyst. sp. 'Kyoga Flameback' in the club as one population. Instead of four separate groups of 10 fish, they could be managed as a larger group of 40 fish... that would take a decent level of communication and planning. Definitely possible. The Bengal tiger species maintenance program in the USA moves tigers around between zoos to optimize genetics. Surely we can transfer fish across town.
    Witamygreatdanes likes this.

    REVTODD Active Member Staff Member

    I will help with any of the cares that I have. If there is a problem , I can see it being that all that I have come from one population.
  8. Dusty

    Dusty Well-Known Member

    It still helps because youre trading your males that have produced fry for you for Randy's males that has not produced you any fry, then you bred your males fry to Randys males fry and the line starts to genetically repair rather than deplete by continious line breeding. :confused: I think?.... Better to breed your aunt rather than your sister.:)(btw, I have no living family so your hillbilly comments will be in vain)

  9. tjudy

    tjudy Executive Board Staff Member

    Unless a group of siblings is completely homozygous, then breeding them together will still end up with some variation in the offspring... but the chance of combining negative recessive genes is much greater when spawning siblings to each other. If the population is large, a few of the fish in the colony can be siblings. Perfect situation? No... but better than breeding a group that is entirely siblings.

    REVTODD Active Member Staff Member

    100% the right direction!
  11. Marine590622

    Marine590622 Advisory Board Staff Member

    So anyone with the flamebacks want to trade males.
  12. bahamafj11

    bahamafj11 Well-Known Member

  13. bahamafj11

    bahamafj11 Well-Known Member

    Randy and I swapped three males, big change! The girls all striped up and are putting the boys through some pretty severe hazing! Hope they are up to the challenge. Cool for me to watch, not sure they are diggin' it, though.
  14. Cinnamonsticks

    Cinnamonsticks Moderator

    Are there some observations that I could make with my 29 gallon with my cory cats 3 f and 3 m that would be helpful? I know four of them are too young for erotica...
  15. Witamygreatdanes

    Witamygreatdanes Active Member

    Mostly, I don't want to part with my males, but would be happy to trade females... also possibly including other clubs that would be willing to get "in" on the action could bring in a total outcross. Or maybe someone would be willing, I know I am, to purchase a totally new clean group of breeding fish to bring in a totally new line or strain. :) Once I have pretty males, I get attached and don't want to move them. In dogs, males have the most possiblity of producing the most get since multiple people breed to the same male because people stand them at stud, in fish, it shouldn't matter which is traded since there is no "public stud service" unless someone wanted to try to implement that by sending a female or 2 to be bred to another person's male..

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