# Reproduction session. Concluding remarks

Bernard Breton, Z. Yaron

► To cite this version:

Bernard Breton, Z. Yaron. Reproduction session. Concluding remarks. Aquaculture of cyprinids. L'aquaculture des cyprinidés, INRA, 1986, 2-85340-791-8. hal-01600778

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# Concluding remarks

The majority of the communications presented at the oral and poster sessions could be grouped around two important problems concerned with the culture of carp and related species, namely, the effects of the environment and spawning induction. These problems were dealt with at both the practical and the theoretical levels. It was only natural to focus the round table discussion around these problems.

## 1. Effect of some environmental factors

All the relevant presentations have indicated that temperature is the main external factor affecting reproduction in cyprinids. Although the collection of papers presented at the symposium has not encompassed any paper on photoperiodic effects, there is enough evidence to show that the photoperiod does affect reproduction in some cyprinids like the goldfish, in which there is an interaction between photoperiod and temperature. However, carp, even maintained on a constant light or constant dark regimes, do respond, by gonadal recrudescence, to an increase in the temperature (Horvath).

The significance of the "amount of temperature" as related to carp reproduction was emphasized by Horvath. He recommended the determination of "degree days" to which the fish are exposed in order to predict the proper timing of spawning in carps. This term, which represents the multiplication of temperature by days, was challenged by Bieniarz and by Kime on the grounds that it does not fully reflect the complex situation of temperature effects on carp reproduction. The term may be useful only within the limits of optimal temperatures, especially when it implicates the definition of a critical temperature (Bieniarz). This is in agreement with the fact that gametogenesis does not occur in carp at a temperature below 15°C (Horvath). The possible role of daily fluctuation in the temperature was also discussed, especially in
relation to the daily cycle of hormones (Peter). Woynarovich summarized his experience in this subject and indicated that propagation of the common carp can take place all year round in tropical countries.

Other external factors affecting reproduction in cyprinids were pointed out: stress and stocking density, feeding (Peteri et al., Wiegand) and pollutants (Pathak).

## 2. Induced spawning and artificial fertilization

Under natural conditions, a cascade of glands and hormones "translate" environmental cues to gonadal growth and spawning. The various methods of spawning induction are, in fact, artificial interventions in one or another step of this cascade. Classical hypophysation, although suffering in most cases from the lack of standardization, is still a common practice among carp breeders (Toor; Dwivedi and Reddy). Introduction of a calibrated carp pituitary extract into hatchery practice will, probably, increase predictability of induced spawning by hypophysation (Yaron). Gonadotropins of mammalian origin (HCG), alone or in combination with carp pituitary extract, are not more effective than pituitary extract alone (Epler et al.). The report by Macinthosh and Price does not conform, however, with this view. Nevertheless, several participants expressed the idea that the use of heterologous gonadotropins such as HCG for spawning induction may lead to the formation of antibodies in the recipient fish and interfere with their spawning in subsequent seasons.

The administration of gonadotropin-releasing hormones of hypothalamic origin (GnRH, LHRH) or their synthetic analogues seems to be a better substitution for the classical hypophysation technique. Their potency in raising endogenous gonadotropin levels and inducing ovulation in certain cyprinids was examined by using them alone (Kouril) or in combination with the dopamine antagonist pimozide (Kaul and Rishi; Sokolowska et al., Lin et al.). Moreover, Kaul and Rishi reported that pimozide, even given alone, was effective inducer of ovulation in the mrighal; in other cyprinids such effect was not observed. Nevertheless, Woynarovich complained that his experience with GnRH in characin, fish were not that successful. Pullin remarked that the cost of treatment with GnRH plus pimozide should be reduced in order to be acceptable in developing countries.

The possible toxicity of pimozide or its residues was raised by Fostier in relationship with the welfare of the recipient fish or the consumer. Unfortunately, no studies have yet been performed on the biological half-life of pimozide or its residues in the fish (Peter). The problem for the consumers does not seem to be that severe since females treated for spawning are kept usually as a broodstock in the hatcheries for subsequent seasons and are rarely marketed (Horvath). The paper presented by Lin et al. has indicated that reserpine, an inhibitor of dopamine secretion, can successfully substitute pimozide in carp induced to spawn by GnRH analogues. Nevertheless, the effects of both pimozide and reserpine on egg quality and fish health is yet to be studied.

Another aspect of spawning induction, whether by pituitary extracts or by GnRH, is the receptivity or suitability of the fish to the treatment. Palpation of fish abdomen for softness has been proven to be rather subjective and inaccurate. Ovarian biopsy and subsequent determination of the position of the germinal vesicle (GV) appears to be a more adequate way to determine the suitability of female carp for spawning induction. A high proportion (65 % or more) of oocytes in which the GV has already started migration (eccentric GV) may serve as an indication for a female ready for
treatment (Levavi-Zermonsky and Yaron). In fact, this simple method has been
adopted already by certain hatcheries in Israel (Yaron).

However, the sensitivity of the oocytes to gonadotropin (GTH) may not be
fully reflected by the position of the GV. A more accurate way would be the
*in vitro* examination of ovarian response to the addition of GTH (Epler et al.).
The sensitivity of the oocyte was found to fluctuate in a diurnal rhythm, coinciding with that of the circulating GTH. The daily peak of GTH occurs at 2 p.m. in Poland (Bieniarz) but it peaks in the "Dor-70" carp in Israel around 11 p.m. (Levavi Zermonsky and Yaron). There is not enough information to allow a conclusion whether this difference should be attributed to the difference in daylength or temperature between these countries at the time the observations were made, to genetic differences between the two carp populations, or other possible factors. The *in vitro* determination of ovarian sensitivity to gonadotropin still requires the proper application to the conditions and routine of the hatchery.

The technique of artificial fertilization in cyprinids using the milt
extracted from one male to the spawn of one female seems, nowadays, rather unso-
phisticated. Research is now in progress to objectively assess sperm motility
and viability (Gatty et al.). The amount of sperm produced and the volume of
milt extractable after hypophysation have been determined together with the
optimal amount of sperm required for successful fertilization in the common
carp (Saad and Billard).

The last part of the discussion has dealt with the possible involment
of pheromones in carp reproduction. At high temperature, testicular tissue of
the carp produce *in vitro* a large proportion of testosterone glucuronide.
These results, taken together with the recent findings of Lambert's group in
the catfish, raise the possibility that this or other steroid glucuronides,
secreted in nature by the males, may act as pheromones that induce a surge of
GTH in the surrounding females, leading to the final ovarian maturation, ovu-
lation and spawning. If this will prove to be the case also in cyprinids,
future research should be directed toward the discovery of the pheromones re-
ceptors in the olfactory system in the fish. Immunocytochemical studies in the
goldfish have demonstrated the presence of GnRH in cells and tracts leading
from the olfactory bulbs and nerves to the ventral telencephalon and the ven-
trolateral preoptic area of the hypothalamus (Kah). There is still a gap bet-
ween the findings on carp testicular glucuronides and the putative olfactory
receptors of male pheromones and GnRH containing brain structures in the
females. However, one would wonder whether future research on reproduction may
not lead to a new direction, the use of synthetic fish pheromones for the arti-
ficial propagation of carp and related species.

In summary, the well attended session and the vivid discussion have clari-
fied the fact that the State of the Art in cyprinids reproduction leaves much
to be desired as compared with the situation in salmonid fishes. The situation
in cyprinids other than the goldfish and the common carp is even less satis-
factory. Problems of special interest are the initiation of puberty in cultu-
red cyprinids, especially in the temperature climate; the estimation of ova-
rian sensitivity to induced spawning; calibation of agents utilized in spaw-
ning induction; gamete management for optimal survival, and the study of early
developmental stages.

B. Breton

Z. Yaron
aquaculture
of cyprinids
l'aquaculture
des cyprinidés

NRA

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HYDROBIOLOGIE ET AQUACULTURE

Collection dirigée par R. BILLARD

Déjà parus dans la même collection :

- La Pisciculture en étang (épuisé)

Arbonne-la-Forêt, 11-12-13 mars 1980

R. Billard, éd.

1980, 406 p.

- Le Brochet : gestion dans le milieu naturel et élevage

Grignon (France), 9-10 septembre 1982

R. Billard, éd.

1983, 374 p.

- L'Aquaculture du Bar et des Sparidés

Sète (France), 15-16-17 mars 1983

G. Barnabé et R. Billard, éd.

1984, 542 p.

- Caractérisation et essais de restauration d'un écosystème dégradé : le lac de Nantua

J. Feuillade, éd.

1985, 168 p.

- Gestion piscicole des lacs et retenues artificielles

D. Gerdeaux, R. Billard, éd.

1985, 274 p.

- Précis de pathologie des poissons

P. de Kinkelin, Ch. Michel, P. Ghittino

1986, 348 p.

Editors / Editeurs

R. Billard, J. Marcel

INRA, Département Hydrobiologie

F-78350 Jouy-en-Josas

For sale / En vente

INRA, Service des Publications

Route de St Cyr, F-78000 Versailles

©INRA, Paris, 1986

ISBN : 2-85340-791-8