I was lucky to find an article by Dr. Gentzsch, published in "The Aquarium", Issue 309 in 1995 (pages 13-16) about his long persevering hardwork on inbreeding Hamburg swordtail. With very limited time per day for hobby and language barrier, I inched bit by bit to explore the reading and found it "Wunderbare!" First, I would start by presenting the following impressive data table showing the breeding result from 18 generations of Hamburg inbreed in English (I hope I translated it right ;). According to the article, Dr. Gentzsch spent almost 17 years with the project. Starting from 1972 with a group of 5 Hamburg. They all have clear finnage, which he assumed they were born to the green helleri mother (a popular cross to maintain Hamburg swordtail in Germany at that time, I learned).
A brief note of Development and Selection: - The Red swordtail was introduced to Hamburg swordtail colony and Hamburg offspring was propagated from Red swordtail mother until 1975. Red males were culled early. - In September of the year, the fact that 03 black females who delivered healthy offsprings had encouraged Dr. Gentzsch to switch to Hamburg x Hamburg breed model. The census of population took place when frys reach early juvenile stage (2 - 4 weeks after birth), then all red and green base individuals were culled from the colony. - In 18 generations, the number of black fish on total ranged from 64.2% to 80.4%. Plus, the Red and Green swordtails isolated from Hamburg parents reproduced only Red or Green offspring. Applying Mendelian's law, this range closed to the theoretic ratio 75% Black : 25% others (red and green), suggesting Hamburg pattern was dominant and could be explained as below: + 25% Homozygous Black (SS whereas S for Schwarz, aka. Black) + 50% Heterozyhous Black (Ss) + 25% Homozygous of Red or Green (ss) - The means ratio 71.5% from reality, compare to theoretic 75%, might suggest that a small fatality occurred in Homozygous Black offspring. - Dr. Gentzsch also noticed that in those generations, {F7, F8, F10, F11, F12, F13, F14, F16}, some individuals have pretty black chest, but they couldn't be Homozygous fishes because test cross threw out Red or Green offspring [?] - Especially noted by Dr. Gentzsch, generation F17, F18, there was an significant increase in Green offspring. [?] - Other findings included: + Most black offsprings in the 18 generations had clear finnage and only partially had a reddish fin staining. + A proportion of 10-20% early males vs 80-90% late developed males were noted in each generation, even though it's likely the early males were the first to impregnated females in colony. + Ratio of male vs female is roughly 1:1 + Female from Red or Green proved to have larger litter size. + The sword of Hamburg males predominantly yellow and black, only 10% showed complete black sword, but this population is vulnerable to cancer at older age. Yellow swords with black edge did not appear, while isolated yellow swords were observed. + No sign of experienced mom turn to male in any generation. Source: Hamburger Schwertträger - Eighteen generations of successful inbreeding My genetic note: From my observation of Hamburg swordtail, the black "armor" of Hamburg (Hamburg trait) is more likeky an overlayer on the fish body, made of macro-melanophore highly concentrated. While the skin - underlayer could be stippled with micro-melanophore forming Greenish Gray base color of the wild Helleri, and/or stained with Red pigment, popularly seen in many domesticated swordtail nowadays. In other words, Hamburg trait is independent from Red/Green base color. In term of base color, Red would outweigh Green, correlated with the breeding result from F1 to F16. As Hamburg trait is highly dominant, it should express in all filial generations, and with this black "armor" fully covered, the fish skin color could hardly be observed. This explanation would support the data above, and propose a hypothesis that a cross of Rr x rr from Hamburg parents in F17 resulting the ratio 1 Red : 1 Green. Consequently, F18 could have been resulted from rr x rr Hamburg parents, which threw 100% of Green offspring, with or without Hamburg trait.
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