Capturing, induced spawning, and first feeding of wild-caught Pseudopimelodus mangurus, an endangered catfish species

This study aimed to describe a procedure for sampling, reproduction, and first feeding of the Neotropical catfish Pseudopimelodus mangurus, an endangered fish species. Wild adult P. mangurus specimens were collected in the Mogi Guassu River and subsequently induced to spawn in laboratory conditions. After hand-stripping, the females, the average weight of the oocytes was 143 ± 1.6 g, with a fecundity of 718 ± 49.8 oocytes g-1. The diameter of the oocytes non-hydrated was 1,226.3 ± 47.7 μm to 1,761.2 ± 26.4 μm after hydration. The fertilization rates were 98.00 ± 0.63%, and the hatching rate was 68.94 ± 11.83%. The first feeding was made three days post-hatching with six different treatments, in which the best results arose with sequential feeding with Artemia nauplii, Astyanax altiparanae and Prochilodus lineatus larvae. This condition resulted in a final length of 2,012.7 ± 44.8 μm by the 10th day of the experiment, higher survival (65 ± 0.9%) and lower cannibalism rate (14 ± 0.3%). The data obtained in this study is important for the establishment of reproductive biotechniques, mass production of P. mangurus, and future establishment of ex-situ GenBank.

Effect of feeding frequency on growth, feed utilisation and cannibalism in climbing perch Anabas testudineus (Bloch 1792) fry

A 35 days experiment was conducted to study the effect of different feeding frequencies on growth and feed utilisation in climbing perch Anabas testudineus (Bloch 1792) fry. Four different feeding frequencies in triplicate viz., 2 (T1), 3 (T2), 4 (T3) and 5 (T4) times a day were evaluated. Fry (144 nos.) of climbing perch were randomly distributed in 12 glass aquaria (50 l) containing 25 l of filtered and well aerated freshwater. Formulated pellet feed was prepared and fed @ 6% body weight to all the experimental groups at different feeding frequencies as mentioned above. At the end of the experiment, fishes were sampled to determine weight gain percentage (WG %), specific growth rate (SGR), food conversion ratio (FCR), protein efficiency ratio (PER), survival percentage (%) and partial cannibalism rate (%). Results revealed that the WG% (112.80±2.25), PER (1.65±0.03) and SGR (2.15±0.03) were significantly higher (p<0.05) in T3 group. FCR (1.55±0.03) was lowest in T3 group. Partial cannibalism rate (%) was significantly higher (p<0.05) in the treatment group T1 (6.33±0.88) whereas the survival rate (%) was lowest in T1 (91.66±4.81). The results therefore, indicated that feeding frequency of 4 times a day (T3) could be the ideal feeding frequency for better growth and feed utilisation during fry rearing of climbing perch.

Does Addition of Perch Larvae as Prey Affect the Growth, Development and Cannibalism Rate of Pikeperch Larvae?

Cannibalism occurs in many cultured fish species, especially at the larval and juvenile stages of piscivorous taxa. In farmed percid species, such as pikeperch (Sander lucioperca), intra-cohort cannibalism is a major issue inducing significant losses of the initial stocking density during the first weeks of rearing. Therefore, the present study was designed to investigate the effects of perch larvae (Perca fluviatilis) as live prey on growth, survival and cannibalism in pikeperch larvae under experimental conditions. Additionally, zootechnical and behavioural variables linked to aggressiveness (S postures, attacks, bites and ingestion), and group structures were considered. The survival rate was not different between the two groups (72% with prey vs. 69% without prey), but the cannibalism rate was higher in the group with the prey (28% vs. 10%). The means of final weight and length of pikeperch larvae were higher in the group fed with perch larvae, but size heterogeneity measured by the coefficients of variation for these two parameters did not differ. The specific growth rate was higher in the group fed with perch larvae, but there was no difference between the two groups concerning Fulton’s condition factor. Among all the behavioural variables (aggressiveness, group structure), none differed between the two groups.

Interactions between leaf-cutter ants and fungus garden: Effects of division of labor, age polyethism, and egg cannibalism

Division of labor (DOL), age polyethism, and egg cannibalism all play roles in shaping colony-level population dynamics in social insect colonies. The ways in which these mechanisms interact with one another to shape population dynamics is not currently understood. In this study, we examine how these mechanisms influence population dynamics in colonies of fungus-gardening leaf-cutter ants by developing and studying two sets of models: (1) We study age polyethism contribution to the dynamics of this multi-species interaction model which incorporates mechanisms of DOL; (2) We explore effects of egg cannibalism in colony dynamics and understand how to model such social conflict behavior realistically using different functional responses. Our results suggest that: (a) Age polyethism is important to keep stable population dynamics. (b) Large maturation rate and mortality rate of inside workers induce colony death. (c) Small enough egg cannibalism rate benefits adult worker ant’s growth and (or) development, large proportion of ants performing a given task can promote colony survival, and too large egg cannibalism rate can lead to colony’s death. (d) Increasing energy invested on brood care and (or) the conversion rate between fungus and ants could induce oscillatory dynamics in models with cannibalism.

Eaten alive: cannibalism is enhanced by parasites

Cannibalism is ubiquitous in nature and especially pervasive in consumers with stage-specific resource utilization in resource-limited environments. Cannibalism is thus influential in the structure and functioning of biological communities. Parasites are also pervasive in nature and, we hypothesize, might affect cannibalism since infection can alter host foraging behaviour. We investigated the effects of a common parasite, the microsporidian Pleistophora mulleri , on the cannibalism rate of its host, the freshwater amphipod Gammarus duebeni celticus . Parasitic infection increased the rate of cannibalism by adults towards uninfected juvenile conspecifics, as measured by adult functional responses, that is, the rate of resource uptake as a function of resource density. This may reflect the increased metabolic requirements of the host as driven by the parasite. Furthermore, when presented with a choice, uninfected adults preferred to cannibalize uninfected rather than infected juvenile conspecifics, probably reflecting selection pressure to avoid the risk of parasite acquisition. By contrast, infected adults were indiscriminate with respect to infection status of their victims, probably owing to metabolic costs of infection and the lack of risk as the cannibals were already infected. Thus parasitism, by enhancing cannibalism rates, may have previously unrecognized effects on stage structure and population dynamics for cannibalistic species and may also act as a selective pressure leading to changes in resource use.

Males of the orb-web spider Argiope bruennichi sacrifice themselves to unrelated females

Costs of inbreeding can lead to total reproductive failure and inbreeding avoidance is, therefore, common. In classical sex roles with no paternal care, the selective pressure to avoid inbreeding is mostly on the female, which carries the higher costs. In some orb-web spiders, this situation is very different because females are polyandrous and males are monogynous or at most bigynous. Additionally, females of many entelegyne orb weavers are thought to bias paternity post-copulatorily towards a desired mate. This increases the selective pressure on males to adjust their investment in a mating with regard to the compatibility to a female. Here, we examine whether genetic relatedness influences mating behaviour in the orb-web spider Argiope bruennichi . We mated either a sibling or a non-sibling male to a female in single copulation trials and compared copulation duration, cannibalism rate and female fecundity. Our experiment revealed that males prolonged their copulation duration and were cannibalized more frequently when mating with a non-sibling female. Males mating with a sibling female were more likely to escape cannibalism by copulating briefly, thus presumably increasing their chances of re-mating with a more compatible female. This suggests that males can adaptively adjust their investment relating to the compatibility of a female.