Moscovitz et al. share their expertise evaluating between predation preferences of a prawn and a crayfish over 4 species of snails that are aquacultural pests, explaining the noticed preferences – or lack thereof – by quantifying snail traits.
Freshwater snails are tiny – however in aquaculture techniques, they loom giant. In fishponds world wide, snails act as intermediate hosts for parasitic trematodes that hurt farmed fish by inflicting ailments, damaging gills, pores and skin, eyes and extra. Contaminated fish exhibit lowered development and elevated mortality, leading to monetary losses for farmers.
The most typical approach to cut back parasite-induced ailments, is to by snail-control, i.e., cut back snail abundances within the fishponds. Just lately using non-GMO monosex populations of the tropical large freshwater prawn, Macrobrachium rosenbergii, as a voracious biocontrol agent towards snails in aquacultural fishponds, has been on the rise. Monosex expertise ensures that the complete prawn inhabitants is both all-male, or all-female. In areas of the world the place the prawn is just not endemic, or is just not utilized in mixed-sex aquaculture populations, it is a wonderful, ecologically sound answer, since monosex populations can not reproduce. As practiced in an aquacultural area in Israel since 2017 – the prawns predate on the snails, and the fish well being improves.
Extra not too long ago, advances in monosex expertise have expanded to a different crustacean: the Australian redclaw crayfish, Cherax quadricarinatus. All-female populations at the moment are possible, opening the door to their potential use as a sustainable biocontrol agent as nicely.
Each crustaceans are precious aquaculture merchandise in their very own proper. However ought to farmers battling snails want prawns or crayfish? We got down to check whether or not one predator outperforms the opposite. Click on right here to learn our current analysis, Moscovitz et al., 2026.
Not all snail prey are created equal
Fishponds are sometimes dominated by a set of illness transmitting, typically invasive, freshwater snails, when in our examine area they embrace: Melanoides tuberculata,Thiara scabra, Tarebia granifera and Haita acuta. These species fluctuate extensively in exterior morphology. Some have thick, ornamented shells; others have easy, skinny shells that must be simpler to crack. As a result of dealing with time – the time a predator spends subduing and consuming prey – usually influences prey selection, we anticipated variations in snail morphology to form the predator’s feeding conduct.
Cafeteria experiment
We performed a food-choice, or “snail cafeteria”, experiment to know if any of the predators want a snail species over one other. Every prawn or crayfish was offered with equal numbers of all 4 snail species in an experimental tank and noticed over one week.
We discovered that the prawn was selective (choosy eater) – it clearly most popular first the thin-shelled snail, then made its method in the direction of the thick-shelled and spiny snail. The crayfish, nonetheless, exhibited opportunistic conduct, and resembled a teen in entrance of a full fridge – it simply ate no matter snail it encountered.
Explaining preferences with numbers – measuring probably the most and least most popular snails
To grasp why prawns had been selective with numbers, we quantified shell traits of the 2 extremes – the prawns least and most most popular snails. Snail shell thickness of its most most popular snail, the thin-shelled H. acuta, was 2.5-times thinner than that of its least most popular Thiara scabra. Mechanical compression exams revealed that breaking Thiara scabra required roughly 8 Newtons extra power than breaking H. acuta (don’t fear, the snails had been euthanized in ice). From an vitality maximization standpoint, prawns look like making a “cost-benefit calculation” – favouring prey that yields extra vitality for much less effort. The crayfish, in the meantime, appears much less constrained by shell energy.
Implications for aquaculture and administration
When deployed thoughtfully, each might present a number of ecosystem providers, together with lowering fish illness danger, reducing reliance on chemical pesticides, and providing farmers extra harvestable protein, tailor-made to their fishpond and native market preferences, in a win-win-win situation. Biocontrol doesn’t need to be a trade-off between conservation and manufacturing. With the fitting species and cautious administration, it could improve each.
