Aquaculture Research, 2008, 39, 748^763 doi:10.1111/j.1365-2109.2008.01927.x Gar biology and culture: status and prospects Roberto Mendoza Alfaro1, Carlos Aguilera GonzaŁlez1 & Allyse M Ferrara2 1Facultad de Ciencias Biolo¤ gicas, Universidad Auto¤ noma de Nuevo Leo¤ n, Universidad, San NicolaŁ s de los Garza, Nuevo Leo¤ n, Me¤ xico 2Department of Biological Sciences, Nicholls State University,Thibodaux, LA, USA Correspondence: R M Alfaro, Facultad de Ciencias Biolo¤ gicas, Universidad Auto¤ noma de Nuevo Leo¤ n, Apartado Postal F-96, Cd. Universitaria, San NicolaŁ s de los Garza, C.P.66450, Nuevo Leo¤ n, Me¤ xico. E-mail: [email protected] Abstract (Fig. 1), bony ¢shes that, together with the bow¢n Amia calva, belong to the order Semionotiformes Many lepisosteid populations in North America have (Nelson 1994) and are sometimes grouped as holos- declined and many are now threatened as a conse- teans. This is an ancient group of ¢sh that is older quence of habitat loss and alteration and commercial than most teleosts, dating back to the Cretaceous and sport over¢shing. Over the last two decades, period, approximately 180 million years ago (Wiley morphological, histological and molecular studies 1976). The genus Lepisosteus is composed of four allowed distinguishing between di¡erent phases of species (L. osseous, L. platostomus, L. oculatus and development and the nutritional condition of larvae. L. platyrhincus), while the genus Atractosteus con- Ontogeny of the digestive enzymes of gar larvae indi- tains three extant species (A. spatula, A. tristoechus, cated the possibility to feed them arti¢cial feeds since A. tropicus). early developmental stages. An in vitro digestibility At present, lepisosteids are distributed in North system to test di¡erent feed ingredients has been America, Central America and Cuba, including The used. Important characteristics of arti¢cial diets Isle of Youth (Comabella, Mendoza, Aguilera, Carrillo, were identi¢ed through di¡erent feeding experi- Hurtado & Garc|¤a-Galano 2006). The northernmost ments. Endocrinological studies showed the feasibil- limit is reached by L. osseus in southern Quebec, while ity of altering larval development and the digestive the southernmost limit is reached by A. tropicus in capacity of larvae. Cloning of gar growth hormone Costa Rica (Mora-Jamett, Cabrera & Galeano1996; Or- opened new avenues to enhance growth in the gars. lando 2001).This is also the only species that ranges to Plasmatic vitellogenin was isolated and puri¢ed, to Paci¢c slope drainages (from southern Mexico to Hon- develop a competitive enzyme-linked immunosor- duras). bent assay, which allowed the straightforward In addition to their close phylogenetic relation- separation of males from females to establish ships, the gars share similar ecological roles as top appropriate proportions for reproduction and also predators. Because of the high trophic position and was used to evaluate hormonal protocols to induce relatively long life span of these ¢sh, many lepisosteid gonad recrudescence and spawning. This review populations have declined due to habitat loss and al- analyzes the biology,ecology and physiology of di¡er- teration (dams, channel straightening, road con- ent gar species as a basis for their domestication, struction, £ow alteration, pollution, etc.) and due to mass production of larvae for repopulation experi- over¢shing. The decline of many gar populations ments and for the culture of commercial-size gar. has resulted in research into the feasibility of using captive culture techniques to reduce ¢sheries pres- Keywords: gar, biology, physiology, aquaculture, sure and to restore natural populations. Of the seven nutrition, reproduction gar species, those belonging to the genus Atractosteus have recently motivated much interest in their cul- ture. This importance is principally due to their rapid Introduction growth rate and large adult size, as is the case of alli- The family Lepisosteidae is at present represented by gator and Cuban gars (Aguilera, Mendoza, Rodr|¤guez two genera and seven extant species of non-teleost & Marquez 2002). Moreover, culturing gars o¡ers r 2008 The Authors 748 Journal Compilation r 2008 Blackwell Publishing Ltd Aquaculture Research, 2008, 39, 748^763 Gar biology and culture RMAlfaroet al. Figure 1 Relative total lengths of the seven extant gar species (based on Suttkus1963; Page & Burr1991; Mora-Jamett et al.1997). several additional advantages such as their ability to Mendoza 2000). This review summarizes recent grow in waters of variable quality due to their capability research on the culture of Atractosteus species. to breathe atmospheric air (Hill, Renfro & Reynolds 1972; Smatresk & Cameron 1982) and toler- ance to high ammonia and nitrite levels (Boudreaux, Reproductive biology Ferrara & Fontenot 2007a, b), their resistance to several diseases (Leo¤ n, Aguiar & HernaŁ ndez 1978; Gars spawn seasonally in the £oodplain of large riv- Kulakkattolickal & Kramer1988) and excellent feed con- ers, shallow lacustrine habitats, and tributaries that version rate (FCR) (Aguilera, Mendoza, Comabella & provide protection for their young from predators. Marquez 2006; MaŁ rquez-Couturier,Alvarez-Gonzale¤ z, Lepisosteids seldom display gregarious behaviours, Garc|¤a-Galano, Contreras-SaŁ nchez, HernaŁ ndez-Fra- with the exception of the spawning season, when nyitti, Mendoza-Alfaro, Aguilera-GonzaŁ lez, Garc|¤a- groups of several individuals (some times 20 or more) Galano, Civera. Cerecedo & Goytortua-Bores 2006). may be observed together. Sex ratios of spawning ag- Within this context, the use of new species for gregations are typically skewed towards males (Dean aquaculture production necessarily implies their do- 1895; Holloway1954; Suttkus1963; Rese¤ ndez & Salva- mestication. This process requires, at least, the study dores1983; Aleman & Contreras1987; Chavez-Lomel|¤, of the capacity of those organisms of interest to live Matthews & Pe¤ rez-Vega 1989; Go¤ mez-Go¤ mez 1989; most of their life cycle under arti¢cial conditions Pe¤ rez-SaŁ nchez 1995; Bejerano, Marquez & PaŁ ramo (FAO/PNUMA 1984). Among the main characteris- 1997). The large spawning aggregations will divide tics desired in a species to be domesticated are the into smaller parties containing a female that is at- ability to reproduce in captivity, the likelihood of tended by several males (from two to eight).The smal- spawning in captivity, the possibility of mass larval ler groups will then enter very shallow waters where rearing, adaptability to the consumption of arti¢cial spawning takes place (Dean 1895). However, sex ra- diets and the capability to grow and be maintained at tios vary among gar species. Di¡ering sex ratios have high densities (AQUACOP & Calvas 1990). However, been reported for tropical gar from1:1,3:1to 5:1males most currently cultured species do not possess all of per female (Rese¤ ndez & Salvadores 1983; Chavez- these characteristics (Mendoza 2005). In fact, the Lomel|¤ et al. 1989; Pe¤ rez-SaŁ nchez 1995; Bejerano et al. reasons to initiate the domestication of a species have 1997). Sex ratios of 1:1 male per female for L. platyr- been economical (commercial value of the species), hincus and 3:1 males per female for L. osseus have sociocultural (traditional ¢sheries) and ecological been reported (Holloway 1954). Finally, ratios of 2:1 (over-exploited or endangered species) (Mendoza, and 1:1males per female have been reported for alli- Aguilera, Rodr|¤guez & MaŁ rquez 2000; Rojas & gator gar (Morales1987; Rodr|¤guez, Banda, GonzaŁ lez, r 2008 The Authors Journal Compilation r 2008 Blackwell Publishing Ltd, Aquaculture Research, 39, 748^763 749 Gar biology and culture RMAlfaroet al. Aquaculture Research, 2008, 39, 748^763 Herrera & Garc|¤a1998;Ferrara2001).Becausethesex of VTG as a sex-speci¢c biochemical marker (HernaŁ n- of individuals in most populations of lepisosteids dez 2002; Cortes 2003;Vela 2003; SantillaŁ n, Mendoza, cannot be determined externally, or that techniques Revol, Aguilera & Montemayor 2005; SantillaŁ n2006; for external sex identi¢cation may need to be devel- Orlando, Binczik, Denslow & Gillette 2007). oped on a population by population basis, and sex ra- Vitellogenin was selected for sex identi¢cation be- tios vary among species and may vary seasonally for cause it is the precursor of yolk and is thus speci¢c a given area, techniques to accurately identify sex of to reproductive females. Moreover, the blood, muscle broodstock are needed to establish proper sex ratios and mucus concentrations of VGT increase concur- forcaptive spawning and to optimize fertilization rates. rently with ovarian development. Until recently,accurate sex identi¢cation of brood- Because of the scarcity of wild alligator gar adults stock was a major obstacle in the culture of gars even in northern and central Mexico, plasmatic VTG and though a few studies have documented sexually di- ovarian lipovitellin (VTL) were isolated and puri¢ed morphic external characteristics. Suttkus (1963) re- from female and estradiol-injected male cultured ported that males of L. platostomus, L. oculatus and Alligator gar. Puri¢cation of both molecules was car- L. platyrinchus have a smaller maximum size and ried out by selective precipitation ethylenediamine reach maturation at a smaller size than females. tetra acetic acid (EDTA^MgCl2), followed by molecu- Female spotted gar L. oculatus are reported to have lar weight ¢ltration in Sepharose-6B and ion ex- larger bodies (Redmond 1964) and longer