Biotecnologia Aplicada Elfos Scientiae ISSN: 0684-4551 Vol. 13, Num. 1, 1996

The interrelation between body growth and growth hormone, insulin-like growth factor and prolactin levels in Tilapia (Oreochromis aureus)

Isabel Guillen,^1 Mario P. Estrada,^1 Reynold Morales,^1 Philipa Melamed^2 and Jose de la Fuente^1

Mammalian Cell Genetics Division. Center for Genetic Engineering and Biotechnology. P.O. Box. 6162, Havana, Cuba.

^2 Tel Aviv University, Department of Zoology,Tel Aviv 69978, Israel.

Code Number:BA96023
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Introduction

The growth hormone(GH)and prolactin (PRL) are polypeptide hormones synthesised mainly by somatotrophos and lactotrophos respectively in the anterior pituitary gland of all vertebrates (1), whereas the insulin like growth factors(IGFs) are peptides whose synthesis and secretion in various tissues and particularly in hepatocytes is possible after the stimulation with GH (2).It has been observed that IGFs can mediate the stimulatory action of GH in the longitudinal growth during the early development.

The combined effect of GH and IGFs is responsible for the maintenance of appropriate body composition, cell regeneration and organ function (2). On the other hand PRL is involved in the regulation of reproduction, osmoregulation, growth and development in teleost fishes as in other vertebrates (3). In this study we examined the relationship between different factors such as GH, IGFs and PRL in tilapia grown from hatching to juvenile stages in natural conditions as well as their influence on growth and development.

Materials and Methods

The study was carried during a period of 8 months (June to January).This period of time matches with the stages of development from hatching to juveniles. Body weight in grams and the length in centimeters were measured monthly in 100 to 200 tilapias in natural culture conditions. Pituitaries, liver and blood were extracted monthly and pooled from various animals in order to determine the levels of GH, IGFand PRL in these stages of development. A radioimmunoassay (RIA) for recombinant tilapia GH was used to detect the levels of GH in serum as reported (4) and plasma PRL was determined by ELISA using a polyclonal antibody against tilapia PRL (kindly given by Dr J. A. Martial, Liege University, Belgium) and developed with Horse-radish-peroxidase (Sigma).

We used Northern blot analysis to measure IGF mRNA levels.The RNA was purified from isolated livers as described (5),transferred to nylon filters (Hybond N, Amersham International plc) and hybridized with a tilapia IGFI cDNA probe, and subsequently rehybridized to gliceraldehyde 3 phosphate dehydrogenase to normalize the signals.

Figure 1.

Figura 2.

Figure 1 shows the growth characteristics of tilapia during the period from hatching to juveniles (8 months of development) under natural conditions of photoperiod, water oxygen, (mean value 6,7 parts / million) and water temperature (minimal value of 24,0 C during the winter and maximal value of 29,4 C during the summer).

The increment in body length (square) and weight (diamond) showed a byphasic kinetics with a slow curve between June and October, and a peak starting from October to January. Values are represented as means ae standard deviation.

Figure 2 shows the plasma GH(Sept-Jan) and PRL (Oct-Jan) levels in growing tilapias.Values represent measures from blood pools taken monthly from 100 animals at random. Both hormone levels showed similar curves. Hormone levels depend on different factors like feeding, season, sexual maturation and photoperiod, reaching sometimes high levels of expression, whose increase, in the single case of GH is regulated and go back to low levels by means of negative feedback of IGF-I on GH secretion (2).The increase in GH and PRL levels during Oct-Dec could be related with the growth accleration and sexual maturation during this period. As previously demostrated for rainbow trout (6), GH levels fluctuated from month to month. These GH pulses could be sufficient to assure growth as permanent elevated GH levels may be deleterious for animal.

Acknowledgements

This work was partially supported by the International Centre for Genetic Engineering and Biotechnology Collaborative Research Programme (project CRP/CUB93-05)

 1. Chen Thomas T et al  Fish Physiology 1994;13:179-208.
 2. Hussain Mehboob A. et al NIPS 1995; 10:81-86.
 3. Yoshikawa-Ebesu J.S.M. et al. The Journal Experimental
    Zoology 1995; 271:331- 339.
 4. Melamed Philippa et al. General and Comparative
    Endocrinology 1995; 97:13-30.
 5. Piort Chomczynski et al. Analytical Biochemistry
    1987;162:156-159.
 6. John P. Sumpter. Aquaculture 1992; 100:299-320.

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