Carlos Aguilera

Morphological Description of Alligator Gar and Tropical Gar Larvae, with an Emphasis on Growth Indicators

Abstract Populations of the alligator gar Lepisosteus spatula (also known as Atractosteus spatula) and the tropical gar L. tropicus are declining as a result of commercial and sport fisheries and habitat alteration. Aquaculture represents a short-term approach to population restoration but requires an understanding of the nutritional requirements of early life stages. This paper describes the larval development and growth rates of the alligator gar and tropical gar and identifies morphological indicators of growth and nutritional condition during early life stages. A light-colored dorsal stripe distinguished alligator gar larvae (23-130 mm total length (TL)), whereas tropical gar larvae (22-60 mm TL) could be identified by a pair of brown and yellow lines on the flanks. Larvae of both species adhered to vegetation through the fourth day after hatching (DAH) and began to swim and feed on the fifth DAH. The growth rate of alligator gar larvae was 1.55 mm/d until 10 DAH and 5.06 mm/d thereafter until 15 DAH,...

Morphophysiological studies on alligator gar (Atractosteus spatula) larval development as a basis for their culture and repopulation of their natural habitats

Natural populations of alligator gar (Atractosteus spatula) have declined recentlydue to the effects of commercial and sportfisheries. Aquaculture represents a short-termalternative to restore natural populations, anda first step to accomplish culture of thisspecies is the study of early life stages.Therefore, multidisciplinary research was usedto describe the major morpho-physiologicalchanges taking place during this period. Thestudies serve as a basis for the introductionof artificial diets for culture. Amorphological study distinguished differentnutritional stages, as well as externalindicators of starvation. A histologicalapproach showed the digestive tract to becompletely formed 5 days after hatching (DAH),at the beginning of exogenous feeding.Throughout larval development, intestinalmaturation was followed and a nutritionalindicator based on the mid-gut cell height wasvalidated. The occurrence of pepsin-likeproteolytic activity was detected from fiveDAH, while trypsin, chimiotrypsin andaminopeptidase-like activities graduallyincreased from two to nine DAH. The incidenceof cannibalism in culture conditions wascontrolled by exposure to anti-thyroidcompounds (thiourea – TU) to retard snoutgrowth. This treatment did not effect growthand allowed juveniles to feed on live prey butprevented the consumption of gar larvae of thesame size. Larvae exposed to3,3′,5-triiodo-1-thyronine (T3) had fasterdevelopment, a potentially advantageouscharacteristic for the repopulation of theirnatural habitat. Finally, artificial feeds werewell accepted and resulted in growth ratessimilar to those of gar larvae that were fednatural prey. This has allowed the developmentof a feeding strategy that effectively reducedcannibalism and led to the production of 30 cmjuveniles in four months.

Risk assessment of the ornamental fish trade in Mexico: analysis of freshwater species and effectiveness of the FISK (Fish Invasiveness Screening Kit)

Aquarium trade has been recognized as one of the major pathways of introduction of non-native fishes into new regions. Nearly 43 million freshwater ornamental fish of different species and varieties are annually commercialized in Mexico and there is a high probability for the establishment of some of these species because of their invasive attributes and the diverse climatic zones existing in the country. Within this context, the identification of high-risk species is of paramount importance considering the potential threat to Mexico’s great biological diversity. In the present study 700 freshwater aquarium fish species commonly imported and produced in the country were filtered for synonyms/varieties, resulting in 368 species, which where submitted to revision for invasive reports using specialized invasive species databases. This allowed ranking the main invasive species and the top 30 were subjected to risk analysis using the Fish Invasiveness Screening Kit (FISK). Calibration of FISK was carried out after generating the reports. A receiver operating characteristic curve was made to determine the FISK ability to discriminate between invasive and non-invasive species in Mexico. Thereafter, Youden’s index was calculated and a threshold of 24 was obtained, representing the cut-off value for defining high-risk species. A total of 17 species out of 30 were classified under a high-risk category, among them several species of the genus Xiphophorus, Pterygoplichthys and Poecilia. Most of the species were native to Asia, Central and South America. Some of these species are already invasive in Mexico.

Pollution biomarkers in the spiny lizard (Sceloporus spp.) from two suburban populations of Monterrey, Mexico

Environmental pollution may severely impact reptile species in urbanized areas. The magnitude of the impact is analyzed in the present study using lizard tail tips for the quantitative evaluation of enzymatic biomarkers of pollution. Spiny lizards (Sceloporus serrifer and S. torquatus) were collected from two suburban localities in the Monterrey metropolitan area, Mexico: Chipinque Ecological Park, a natural protected area, and El Carmen Industrial Park (IP), a highly polluted site. Different enzymes were used as biomarkers including: acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline phosphatase (ALP), acid phosphatase (ACP), superoxide dismutase (SOD) and glutathione S-transferase (GST). The levels of AChE, BChE and ACP activity were not significantly different between localities. AChE and BChE, commonly used as biomarkers of neurotoxic polluting agents (e.g. organophosphate pesticides) do not appear to be affecting the populations from the study locations. In contrast, the levels of CaE, GST, ALP and SOD were significantly different between the localities. These biomarkers are regularly associated with oxidative stress and processes of detoxification, and generally indicate pollution caused by heavy metals or hydrocarbons, which are common in industrial sites. The data resulting from the analysis of these biomarkers indicate that these polluting agents are affecting the populations of Sceloporus in IP. The present work validates the possibility of conducting additional ecotoxicological studies using biomarkers in combination with a nondestructive sampling technique in species of spiny lizards that are abundant in many North America areas.

Effectiveness of Synthetic Molecules, and Animal and Vegetable Extracts as Baits for Harvesting Red Swamp Crayfish, Procambarus clarkii

Abstract The present study was designed to evaluate the efficiency of different biogenic amines (putrescine, cadaverine, tyramine, spermine and spermidine) and their precursory amino acids (arginine, histidine, lysine and tyrosine), as well as animal extracts (from fish, crustaceans and mollusks) and vegetable extracts (Chara sp., coconut and alfalfa) as baits in traps for red swamp crayfish, P. clarkii. The methodology was conceived as a logical sequence to proceed from rapid screening of a large number of treatments and was divided into three phases: (1) chemo-detection bioassays, (2) chemattraction bioassays, and (3) field bioassays carried out under natural conditions. The attractants that showed the best performance as baits for P. clarkii, were: the fish soluble extract (included at 2.96%), the putrescine (included at 0.30%) and the red crab soluble extract (included at 2.69%). The benefits of using these attractants, when added to common pelleted feed, come from their low cost, availability and enhanced handling properties.

Ecotoxicological Biomarkers in Multiple Tissues of the Neotenic Ambystoma spp. for a Non-lethal Monitoring of Contaminant Exposure in Wildlife and Captive Populations

Amphibians are the most threatened vertebrate group with a third of currently known species endangered with extinction, as a result of climate change, habitat loss, disease-introduced exotic species, and pollution. Because of their vulnerability, they have often been used as environmental quality indicators, as well as laboratory models for toxicological research. Given the sensitivity of amphibians to changes in their surrounding environment, including pollution, it was deemed important to define a non-lethal technique based on the evaluation of a set of biomarkers in different tissues of neotenic individuals of Ambystoma velasci. The levels of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline and acid phosphatases (ALP, ACP), glutathione s-transferase (GST), 7-ethoxyresorufin-O-deethylase (EROD), and superoxide dismutase (SOD) activities, as well as the oxygen radical absorption capacity (ORAC) were measured in tail, gills, liver, plasma, and brain samples. Significant tissue-specific differences were observed for all biomarkers with the exception of ACP. The highest values of specific activity for most biomarkers were detected in the liver. However, the levels measured in gills were very close to those observed in the liver and showed fewer variations than other tissues. These findings suggest that the sampling of gills could be used to evaluate pollution biomarkers in salamanders without apparent harm, as this tissue quickly regenerates.