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ll though similar in looks, habits and often confused by the aquarist, Corydoras hastatus and C. pygmaeus, Knaack,1966 have differing reproductive modes. Previous efforts to induce C. hastatus to spawn have met with no success, although spawning of their own volition had been observed in my Corydoras community tank, where two young C. hastatus have been produced over a six-month period.

 

Gastrodermus hastatus

C. hastatus may not have spawned in the prepared tank because only ten fish were available - 5 males, 3 females and 2 juvenile fish. This I felt was a little low in numbers as C. hastatus are a naturally shoaling fish.

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My total stock of 10 C. hastatus were introduced into a 61cm x 25cm x 25cm tank filled to 10cm with stock tank water (pH 6.87 Temp. 72°F). Substrate was Dorset pea and sandy outcrops. The tank was planted with different Cryptocoryne's and pieces of bogwood. After the fish were introduced the tank was topped up with fresh tap water - Temp. 72°F. the tank was lit by room lighting.

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A week and several water changes later, the C. hastatus were very inactive. All of them were hiding at the rear of the tank and were seldom seen shoaling in the normal manner. This action was expected. I decided to introduce 10 C. pygmaeus. This should lift the C. hastatus off the gravel and make them feel more at ease.

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It had paid off. Both C. hastatus and C.pygmaeus were shoaling together and feeding well. Water conditions were pH 6.8, temp. 72°F.

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The fish have been observed for the past few days and the extra fish have made a great difference. C.pygmaeus spawned, laying 40 - 50 eggs on the front glass and on the plants. The spawning was typical of C. aeneus (Gill,1858) and C. paleatus (Jenyns, 1842)., i.e. plenty of activity. The C. pygmaeus were not removed as the C. hastatus have become very active and the eggs were not being eaten. Checking the tank that evening, 5 male C. hastatus were seen chasing one female. There was a very interesting point the female's eyes were completely black. The iris was not visible - only the pupils could be seen and they were jet black. The males chased the female for 2 hours and no eggs were laid. I was ready to give up when I noticed the female with one very small egg held firmly in her ventral fins. Actual delivery of the egg was not seen, but the males were all quivering round her at this time. (The other females were shoaling with the C. pygmaeus and their eyes were normal. With the egg cradled in her ventral fins, she then began to swim over and under the plant leaves with the males in close pursuit. They seemed to be cleaning the leaves. She swam around with the one egg for half an hour, before depositing it under a plant leaf. I am quite sure only one egg was laid at this time.

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This spawning activity has continued in the evening for 2 weeks. Only one female spawning at a time, and laying only one egg. Whether or nor it is the same female each time is hard to tell as they are all similar in size. During the period when the C. hastatus spawned, fry were seen in the tank. They were silver in colour with 2 - 4 dark patches along the back. Some had a distinct black patch through the caudal peduncle. As the fry grew, 4 C.hastatus fry of varying sizes were seen swimming with the 30 C. pygmaeus fry.

OBSERVATIONS

1) To date (mid- March). The C. pygmaaeus have not spawned again, but still the odd C. hastatus appears. Could the C. hastatus be a periodic spawner, as are some of the Julidochromis species from Lake Tanganyika?

2) The eyes of the spawning female turned completely black. The gold iris vanished and the full eye appeared black.

3) The growth rate of the C. hastatus is quicker than that of C. pygmaeus. The older C.hastatus are 1cm whereas the 30 C.pygmaeus are under 6mm.

4) Feeding: Powder food was fed as soon as the first fry were seen and thereafter every day in small quantities for any newly hatched fry. Brine shrimp and micro worm were fed along with normal daily food for adult fish.

5) Regarding the high mortality rate reported by some aquarists, which can occur at 4/ 6 weeks period, i.e. the fry will try to lift to the water surface and spin to the bottom (water depth does not matter). The fry were very weak and wasting away and would die in a week. The size of the fry seems to be the important factor - not the age. I have a few theories:

a) At first I thought that a nutritional deficiency was the trouble. If the fry were left with the parents the high mortality rate did not occur. Perhaps the parents helped feed the fry, or they received nutrition from mulm caused by the parents. Of course you will lose some due to the parents eating fry or eggs. No deaths occurred. Could the fry be developing their secondary breathing system and getting chilled (as do anabantids when the labyrinth organ is developing). Lately, a very high success rate with C. barbatus (Quoy & Gaimard,1824) and C. aeneus, with the parents removed, perhaps the tanks were higher than normally used and so water and air temperature were not equal Or can it be put down to bad management.

This article first appeared in the Catfish Association of Great Britain Newsletter !982.

 

Photo Credit: © Reinhold Wawrzynski

Update: Corydoras hastatus is now Gastrodermus hastatus.