Assessment of the predatory capacity on mosquito larvae of Jenynsia multidentata (Anablepidae) in presence of vegetation under laboratory conditions

ABSTRACT Larvivorous fish have been studied as potential biocontrol agents of mosquito larvae and pupae through their trophic interactions. The use of native fish for mosquito control may have benefits for both aquatic biodiversity and human health. Evaluating the effect of vegetation on the predatory efficacy is fundamental to determine if this species can be used as a biocontrol agent. With the aim of evaluating Jenynsia multidentata (Jenyns, 1842) as a biocontrol agent of Culex pipiens Linnaeus, 1758, we tested its predatory capacity in the presence or absence of aquatic vegetation under laboratory conditions. Two independent experiments were conducted. Larval consumption at a density of 60 larvae (6 larvae/l) was significantly reduced with the vegetation increased. On the other hand, when the larval density was 120 (12 larvae/l), the predatory capacity of J. multidentata did not vary in the presence or absence of vegetation. This result indicated that vegetation effect on consumption could be related to prey density, since at the higher density of prey the probability of predator-prey encounter might be increased. Jenynsia multidentata is a good consumer in presence of vegetation and could be used as a potential biocontrol agent of mosquito larvae in natural environments with similar characteristics to the ones tested in these experiments.

A macroscopic classification of the embryonic development of the one-sided livebearer Jenynsia multidentata (Teleostei: Anablepidae)

ABSTRACT This study proposes eight stages according to the main discernible changes recorded throughout the embryonic development of Jenynsia multidentata. The development of morphological embryo structures, pigmentation, and changes in tissues connecting mother and embryo were included in the stage characterization. From the fertilized egg (Stage 1), an embryo reaches the intermediary stages when presenting yolk syncytial layer (Stage 2), initial pigmentation of the outer layers of the retina and dorsal region of the head (Stage 3), and the sprouting of the caudal (Stage 4), dorsal and anal fins (Stage 5). During the later stages, the ovarian folds enter the gills, and the body pigmentation becomes more intense (Stage 6), the body becomes elongated (Stage 7), and there is a greater intensity in body pigmentation and increased muscle mass (Stage 8). The dry weight of the batches varied between 0.6 ± 0.3 mg (Stage 3) to 54.6 ± 19.7 mg (Stage 8), but the dry weight of the maternal-embryonic connecting tissues remained almost constant. After controlling the effect of those reproductive tissues, the gain in dry weight of the batches throughout development increased exponentially from Stage 6, reflecting the increase in size and weight of the embryos due to matrotrophy.

A Bayesian analysis of the parasitic ecology in Jenynsia multidentata(Pisces: Anablepidae)

ABSTRACT Jenynsia multidentata Jenyns, 1842 (one-sided livebearers) are euryhaline viviparous fish of small size, used in the laboratory experiment, important as resource for biological control of mosquito’s larva and a key species to recover eutrophic lakes. Works have been published dealing with parasite biodiversity of this host, but little has been studied about the parasite community ecology. From early 2009 to ends of 2010 specimens of J. multidentata were collected from two places, the Salado Relief Channel (S.R.C.) on Samborombón Bay and the Sauce Chico River near to the city of Bahia Blanca (B.B.). All fish were sexed, measured and grouped into sizes/age classes. The fishes from both sites harbored 16 parasitic species: nine digenean, one monogenean, one metacestode, one acanthocephalan, two nematode and two copepods. Lecithaster confusus Odhner, 1905, the metacercariae Hemiuridae gen. sp. indet., metacercariae Thylodelphys sp. (inside the eye), Glossocercus sp. nematode L4 (intestine) and Ergasilus sieboldii Nordmann, 1832 are new records for the host. The high number of larval stages made of this fish a link between micro and macroecosystems. The size 2 had the higher biodiversity in both sites, which could be the most suitable age to store the maximal number of parasite of the environment and have a more equitability in their distribution on the host. In B.B. some parasites had higher prevalence and mean abun dance due to the small size of the waterbody compared with the S.R.C. Despite that, in S.R.C. exist a higher specific richness and biodiversity due the daily flow of saline and freshwater and proximity of the sample site to the mouth of the channel in the bay. This is the first approximation to an analysis of the parasitic ecology on this host.