Jérôme Lazard

Larval rearing of the Asian Catfish, Pangasius bocourti (Siluroidei, Pangasiidae): alternative feeds and weaning time

Abstract Three experiments were carried out to evaluate Pangasius bocourti larval rearing with different feeding regimes. In the first experiment, survival rates of larvae fed on Artemia nauplii, cladocereans (Moina sp.), or red-blood worms (Tubifex) were not significantly different, 91–93%. However, Artemia nauplii and Tubifex gave similar growth rates (35–36% day−1) while Moina sp. resulted in lower growth. Commercial trout-starter feed resulted in the lowest survival (67%) and growth rates (20% day−1) when compared to live feed. In the second experiment, feeding dry feed based on yeast and beef liver or feeding decapsulated Artemia cysts improved survival rates. These were 90% and 87%, respectively, not significantly different from Artemia nauplii. Regarding growth, dry feed and decapsulated Artemia cysts resulted in lower growth rates than Artemia nauplii. These were 23% and 29%, respectively. Stomach content analysis showed that reduced growth in decapsulated-cyst fed larvae compared to live Artemia reflected a difference in feed ingestion and preference rather than a difference in nutritional quality of the feed. In the third experiment, it was shown that larvae require 3-day feeding on Artemia nauplii before weaning them on to trout-starter feed to prevent negative effects on growth. Three days after initial feeding, fish stomach attains its biological and physiological functions.

Induced ovulation of Pangasius bocourti (Sauvage, 1880) with a progressive hCG treatment

Abstract The Mekong catfish Pangasius bocourti (Pangasiidae, Siluriforme) has been widely cultured in southern Vietnam in floating cages since 1989 (15,000 tonnes annually). However, the supply of fingerlings has been dependent on catches from the wild, which has led to a reduction in the natural resources. Reproduction of P. bocourti was studied with brooders reared in earthen ponds or in floating cages on the Mekong River. Brooders did not show any sexual dimorphism but females were more developed than males in terms of body weight (+26%) and fork length (+7%). Induction of oocytes maturation and ovulation required a progressive hormonal treatment in two steps. Several daily injections of hCG at a low dose (500 IU kg −1 ) were applied first. These injections induced the development of ovarian follicles, indicated by an increase in their diameter. The second step consisted of two successive hCG injections applied at higher doses (1500 and 2500 IU kg −1 ) at an 8–10-h interval, which induced oocytes maturation, followed by ovulation at 19±3 h after the first injection. Mean ovulation and hatching rates were 66% and 55%, respectively. Ovulation was generally induced once a year for each female although a second ovulation could be obtained for some individuals in the same reproductive season. Fecundity was highly variable, from 400 to 16,700 ova kg −1 , and average fecundity in ponds was twice as high as in cages.

Induced spermiation and milt management in Pangasius bocourti (Sauvage, 1880)

Abstract Males of Pangasius bocourti (3.3–6.9 kg) raised in floating cages on the Mekong River were used to study the production of milt and its use for fertilization. Although spontaneous spermiation occurred in mature males, the average volume of collected milt was low (26.5 μl kg −1 ). A single human chorionic gonadotropin (hCG) injection (2000 IU kg −1 ) induced a 13-fold increase in sperm volume, 12 h after injection (344.5 μl kg −1 ). The associated sperm concentration and production were 26.9×10 9 spz ml −1 and 8.4×10 9 spz kg −1 , respectively. Injection of GnRHa (30 μg kg −1 ) with domperidone (3 mg kg −1 ) induced a lower increase of sperm volume and sperm production. The motility of spermatozoa (spz) in well water lasted only 57 s, but was doubled in low saline solution (NaCl 34 mM). Crude milt could not be stored but five-fold dilution in immobilization solution (NaCl 207 mM) allowed fertilization to be postponed for 36 h. Fertilization was triggered by well water with milt diluted 1000 times.

Assessing aquaculture sustainability: a comparative methodology

Little work dealing with the evaluation of aquaculture system sustainability has so far been undertaken on a global and comparative basis. Moreover, such work is mostly based on very unbalanced approaches in terms of the dimensions of sustainable development that are taken into account. The approach adopted in this article is designed to encompass all the dimensions of sustainability including the institutional one (governance). The taking into account of this latter, in particular, together with the role played by aquaculture in sustainability at the territorial level gives the approach its original and innovative nature. The process of establishing the checklist of sustainability indicators in aquaculture relies on a hierarchical nesting approach which makes it possible to link indicators with general sustainability criteria and principles. At once multidisciplinary and participatory, the approach compares several countries with highly differentiated types of aquaculture system. An original finding from this work is that the technically most intensive farming model scores better than more extensive systems, which might have been thought to be closer to natural systems in their environmental dimension and therefore intuitively more ‘sustainable’. This result suggests relating sustainability outcomes to the level of control and of devolved responsibilities.

Evaluation of Aquaculture System Sustainability: A Methodology and Comparative Approaches

Over the last 30 years, aquaculture has experienced an unprecedented development in global animal production with an average yearly growth rate of over 10% between 1980 and 2000 (FAO, 2009). During the same period, capture fisheries saw their progression gradually grind to a standstill and growth stopped from 1995 (total catch fluctuating between 90 and 95 Mt/year according to the year). The growth of aquaculture, despite its benefits and the fact that it is the only way to meet the increase in demand for sea products, evaluated at 270Mt in 2050 (Chevassus au Louis et Lazard, 2009; Wijkstrom, 2003), raises a certain number of issues directly related to its sustainable development. Amongst these are issues related to feed for the farmed organisms, to their biological diversity, to the farms’ economic sustainability, to the impact of aquaculture development on social equity and to the set of arrangements constituting the sector’s governance. Feed, for example, is currently the subject of significant controversy as shown by the emblematic article of Naylor et al. (2000) that exposes the impact on catches of the massive use of fish meal and fish oil in fish and prawn aquaculture and advocates the return to sparser aquaculture systems, directly inspired by traditional Asian systems which use more extensive techniques based on polyculture and fertilisation and where artificial feed is only seen as a potential supplement. This diagnosis, although interesting as it generated much debate, was, however, incomplete and, in fact, inaccurate: by focusing on a single criterion and a single dimension (environmental) of sustainability, the authors were led to make proposals that had no chance of being adopted by the actors. De facto, farming systems have continued to intensify and this has led to a sustained increase in the use of

Changement climatique et agricultures du monde

Depuis quelques années, et à l’approche de la 21 Conférence des parties des Nations unies sur le changement climatique qui se tiendra à Paris fin 2015, le nombre de publications, congrès et autres conférences sur le changement climatique est en croissance exponentielle. Pourtant, il est un domaine où demeurent encore de nombreuses incertitudes. Dans les zones rurales tropicales, les modélisations prévoient de multiples dérèglements mais les tendances ne sont pas claires alors que le constat de l’impact du changement climatique sur les populations les plus pauvres est souvent alarmiste. Comment satisfaire la sécurité alimentaire tout en s’adaptant au changement climatique et en l’atténuant ? Quelles sont les principales menaces pesant sur les agricultures du Sud ? Comment les agriculteurs du Sud répondent-ils à ces menaces ? Quelles sont les propositions de la recherche agronomique ? Quelles sont les voies encore inexplorées ? Les recherches en cours nous interpellent. Elles couvrent un immense champ scientifique et montrent que des solutions existent, aussi diverses que de nouvelles pratiques agronomiques, la gestion de l’eau, le recyclage des résidus agricoles, le diagnostic des maladies émergentes ou les paiements pour services écosystémiques. Notre compréhension des mécanismes financiers et politiques qui sous-tendent les négociations climatiques internationales est indispensable pour penser avec les agriculteurs des options concrètes de réponse aux enjeux du climat tout en répondant aux exigences du développement durable. Ce livre, dense, précis mais facile à lire, regroupe les expériences de plusieurs dizaines de chercheurs et agents de développement de toutes disciplines.