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The Effects of "Photoperiod"
Oct 1982: Vol.5, # 10-Part VI

Published with permission from BowTie Inc., publisher of FishChannel.com.

 

In the author's recent articles on Angelfish Genetics, the discussion has concerned pigment patterns produced by mutant genes and also by various combinations of these genes. All of this information pertained to angelfish raised with a 14 hour photoperiod. However, the discovery has been made that continuous light affects the pattern of not only silver angelfish but of some other genotypes as well.

Years ago a local aquarist, Richard Pohl, told me that his silver angelfish raised in continuous light lacked the striped pattern. In a corner of his fish room he kept a light bulb turned on day and night to provide heat for brine shrimp hatching. Young silver angelfish in the tanks that were exposed to this light did not develop stripes, but those raised in tanks that were in the dark at night had the usual stripes.

Fig. 1: Wild-type (silver) 14 hours light.
Fig. 2: Wild-type (silver) continuous light.

In my recent FAMA articles on angelfish genetics I discussed pigment patterns produced by mutant genes and also by various combinations of these genes. All of this information pertained to angelfish raised with the lights on about 14 hours per day. However, I have discovered that continuous light affects the pattern of not only silver angelfish as Richard Pohl found, but of some other genotypes as well. I did not notice any difference in either marble or smokey angelfish raised in a 14-hour day compared with those raised in continuous light. Some of the other genotypes that I have tested with a 24-hour day are the subject of this article.

Fig. 3: Genetically wild type, this female's lack of stripes may have been caused by exposure to continuous light during her early life.
Fig. 4: Zebra (one dose of the gene for zebra) 14 hours light.

Compare the usual pattern of wild-type (silver) raised in a 14-hour day (Fig. 1 above) with a silver without stripes that was raised in continuous light (Fig. 2 above). I obtained, from an aquarium shop, a female that genetically was wild-type. She produced all wild-type offspring when mated to a wild-type. However, this female had no body stripes and had a few small black spots on the body (Fig.3).

Fig. 5: Zebra (one dose of zebra), continuous light for 136 days, then 14-hour day for 2 months.
Fig. 6: Male zebra (one dose of zebra), continuous light for five months, then 14-hour day for 2 months.

A zebra angelfish raised in a 14-hour day has three prominent vertical stripes on the body (Fig. 4). Single-dose zebras raised in continuous light for 136 days from the spawning date had numerous black dots on the body, and were the same after two months in a 14-hour day (Fig. 5).

Another spawn of single dose zebras that were kept in continuous light for five months and then a 14-hour day for two months had some black spots and also some narrow, vertical, partial stripes (Fig. 6 and Fig. 7).

Fig. 7: Female zebra (one dose of zebra), coninuous light for five months, then 14-hour day for 2 months.
Fig 8: Black lace (one dose of dark) 14-hour day.

The black lace angelfish, which has one dose of dark, is similar to silver but darker-colored (Fig. 8). Raising a black lace in continuous light results in a dusky-colored fish with little or no evidence of stripes on the body. At 54 days after they became free-swimming, these black lace were dusky-colored and had a faint dark vertical stripe on the rear part of the body. After being raised for a total of 63 days in continuous light, these fish were changed to a 14-hour day.

Fig. 9: Black lace, coninuous light for 63 days then 14-hour day for 11 months. Faint vertical stripes show part of the time.
Fig. 10: Black lace, coninuous light for 63 days then 14-hour day for 11 months. No vertical stripes showing when this photo was taken.

Eleven months later, they still were dusky-colored, with faintly darker vertical stripes sometimes showing (Fig.9) and other times fading completely (Fig. 10).

In this case the dusky, almost stripeless, pattern was set by only about two months of continuous light, and this pattern did not change to the usual black lace pattern even after 11 months of a 14-hour day. As I shall point out in the next article, not all patterns are set by two months of continuous light.

Fig. 11: This true black (two doses of dark) was raised in continuous light until it was quarter body size; it has no stripes. The photo was taken a year later, after the fish was kept in a 14-hour day during that year.

A true black angelfish, having two doses of dark, has vertical stripes that can be seen by shining a strong light on the body with a flashlight; this is the pattern that develops if the lights are turned off at night during the early part of the fish's life. However, if you raise true black angelfish in continuous light, the body will be solid, velvety black with no stripes (Fig. 11).

In the following cases it would be difficult or impossible to know the genotype of an angelfish by its appearance if you know nothing about its parents or how it was raised:

(1) A fish having one dose of stripeless may have one or a few black blotches, or it may have none, on the body. If it has no black blotches, it looks like a wild-type (silver) that was raised in continuous light. The fish can be tested by mating it to a wild-type, raising the offspring with the light turned off at night. If the tested fish has one dose of stripeless, half of its offspring will lack stripes. If the tested fish is wild-type that was raised in continuous light, none of its offspring will lack stripes unless both parents carry the recessive gene for new gold, in which case some golds will appear in the offspring.

(2) A black lace (one dose of dark) raised in continuous light may resemble a butterfly (one dose of dark and one dose of stripeless) that was raised with the lights off at night. The fish can be tested by mating it with a wild-type and raising the young with the lights off at night. If the tested fish is black lace that was raised in continuous light, 50% of the offspring will be black lace and 50% will be wild-type. If the tested fish is a butterfly, the offspring will consist of wild-type, stripeless, black lace, and butterfly.

(3) A black with no stripes could be a true black (two doses of dark) raised in continuous light. Or it could be a true black with one dose of stripeless, raised with the lights either on or off at night. I have not raised in continuous light any blacks having one dose of dark and one dose of new gold, which have stripes when raised with the lights off at night. You can test a black to find out if it has one dose of stripeless by mating it with a wild-type; raise the offspring with the lights off at night. If stripeless is not present in a true black, this cross will produce 100% black lace offspring. If the true black has one dose of stripeless, you will get black lace as well as butterfly, which does not have stripes on the body.

Several years ago Jack Wattley told me about some discus without vertical stripes that another aquarist had reported to him. I asked Mr. Wattley if those discus had been raised with the lights on or off at night. He replied that it was interesting that I asked, since he understood that these discus had been raised in continuous light. I did not follow up on the matter, but think long day length should be considered as a possible cause of no stripes in discus.

 
 
 
 
 
 
 
 
 
 
 
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