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Two groups of 4- to 5-month-old catfish, Heteropneustes fossilis, were studied 2 years apart, in each case after standardization in light for 12 hours, alternating with darkness for 12 hours. The two studies involved 5 groups of 10 catfish each and 10 groups of 17 catfish each, respectively. In each study some fish were allowed access to food only during certain times in the circadian cycle: early dark, late dark, early light and late light for 45 or 50 days. On the average, in both studies, the catfish on restricted feeding schedules gained in body weight but more so when fed at certain times in the circadian cycle as compared to others. A circadian rhythm in weight response was demonstrated by a zero-amplitude test associated with the fit of a 24-hour cosine curve to the data (P less than 0.03). The acrophase (time of high values) for body weight gain occurred consistently either near the middle or in the second half of the daily dark span. That is, body weight gain in the presumably dark-active catfish seems to be maximal when food is made available in the middle or later part of the daily dark span. In catfish, as in human beings and mice, the timing of food intake can serve to optimize the utilization of ingested calories, by mechanisms yet to be elucidated.

The annual reproductive cycle of the catfish Heteropneustes fossilis is divided into the preparatory period (February–April), prespawning period (May–June), spawning period (July–August), and postspawning period (September–January). Ovarian recrudescence, which normally occurs during the prespawning period, can be advanced by photothermal manipulations. During the postspawning and preparatory periods, the tempo of ovarian recrudescence is much faster at 30 C than at other temperatures (ambient, 25 or 34 C) regardless of photoperiod (14L + 10D, 12L + 12D, or 9L + 15D).Warm temperature (30 C) postpones the postspawning ovarian regression only up to the first week of October regardless of photoperiod. The ovarian cycle is regulated by a circannual rhythm which can be activated 5 mo earlier, but its activity cannot be prolonged beyond October by photoperiodic and temperature manipulations.Interruption of the night of a short day (6L + 18D) treatment by 1 h of light between 0000 and 0100 induces ovarian recrudescence that is significantly greater than that obtained in the control group exposed to 7L + 17D. Scanning of the major part of the dark period (1800–0500) to determine the duration of the photo-inducible phase shows that it lies between 0000 and 0500 with peaks from 0000 to 0100 and from 0400 to 0500. Even 1 h of light in a regimen of 1L + 23D presented between 1900 and 0500 produces significant ovarian recrudescence with peaks between 2200 and 0100. These results clearly demonstrate the possible involvement of a circadian mechanism for photoperiod measurement in the catfish.Precociously gravid catfish obtained as early as April by photothermal treatment have been induced to spawn in the laboratory by administration of ovine luteinizing hormone (LH). Ripe eggs after fertilization hatched into seemingly normal fry. Further, the spent fish when subjected to the same photothermal treatment developed a fresh crop of yolky eggs within 1 mo; such gravid females have been again induced to spawn with LH. This process has been repeated so that the same set of fish have been spawned 4 times between April and July of the same year. Thus, it is possible to get catfish fry not only early but also 2.6 times more than that usually available from each female during the spawning season. The aquacultural potentialities of this laboratory discovery are discussed.

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A seasonal study of the seminal vesicles i n relation to that of the testes has been conducted i n the catfish, H . fossilis. The annual reproductive cycle of the catfish has been divided into ( i ) Preparatory period (February-April), (ii) Prespawning period (May-June), (iii) Spawning period (July-August) and (iv) Postspawning period (September-January). Testes exhibit initiation of spermatogciiesis in the midpreparatory period, but significant increase i n weight of the testes accompanied by active spermatogenesis occurs during the prespawiiing period. In the spawning period, the testes are maximally enlarged and their seminiferous tubules are packed with spermatozoa. Following spawning; the testes gradually regress in the postspawning period. The seminal vesicles show initiation of secretory activity during the preparatory period but their recrudescence lags behind that of the testes by about a month. The seminal vesicles attain maximum weight and secretory activity during the spawning period. Thereafter, the seminal vesicles regress precipitously and sooner than the testes.The histochemical and biochemical studies on the seminal vesicles indicate that the secretion contains mucoproteins, acid mucopolysaccharides, primary proteoses. besides traces of phospholipids and native proteins.

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