Invader Xan
Fish Crazy
I'm hoping this is more what you're looking for in this section. Any criticism on my posting is welcomed, along with any scientific discussion regarding the subject matter. Your own opinions on intelligence in decapods and other invertebrates are also extremely welcome. 
Most laws and even opinions on cruelty to animals extend only as far as vertebrates. This is a fact. I've heard of people treating crustaceans very badly, the archetypical example being divers removing claws from living lobsters as trophies.
Certainly, decapod crustaceans have fine control over their neurons, enabling them to perform some relatively dextrous tasks. Empirical evidence shows that many decapods can eat snails by simply plucking them from their shells, and many keepers of crayfish cite that a good way to set up their tank is to introduce them into a basic living space and to add ornaments one at a time, enabling the animal to arrange it's own living space. At a fundamental level this could be conjectured as similar to the human tendancy to alter our local environment.
Ocean dwelling decapods have been observed to engage in apparently social behaviour. Lobsters are commonly found in groups on the sea bed and have been observed forming "conga lines" in order to ensure the safe transit of a group of animals across a long distance [The Blue Planet, Sir David Attenborough].
In terms of perception, the majority of decapod crustaceans have exceptionally good eyesight, far better than a great many vertebrates, the Mantis shrimp (stomatopod, not decapod - but also of the class malacostraca) has one of the largest ranges of eyesight wavelengths known (from infrared to ultraviolet) [citation needed]. Decapods also have a wide sensory array for detecting odours, pressures etc.
The main reason cited for people's dismissal of the capacity for intelligence in invertebrates is their brain:body mass ratio, however, most invertebrates have a very different nervous system to vertebrates; being much more decentralised and consisting of a number of ganglia distributed throughout their bodies, and connected by axons. These ganglia are often quite large in relation to the animal's "brain" and are possibly centres for sensory input and processing.
Decapods have also been found to have opioid receptors, and subsequent research has shown that reaction to certain (potentially painful) stimuli is decreased with the administration of morphine. Though further research is needed, many decapods have shown the capacity to learn and make discriminations, including remembering and avoiding threatening objects or situations. Empirical evidence is present on this very forum of pet crayfish and other crustaceans exhibiting 'personalities', and my own personal experience has shown that two macrobrachium shrimp of the same species can react very differently to certain stimuli, doubtless based on past experience.
Most laws and even opinions on cruelty to animals extend only as far as vertebrates. This is a fact. I've heard of people treating crustaceans very badly, the archetypical example being divers removing claws from living lobsters as trophies.
Certainly, decapod crustaceans have fine control over their neurons, enabling them to perform some relatively dextrous tasks. Empirical evidence shows that many decapods can eat snails by simply plucking them from their shells, and many keepers of crayfish cite that a good way to set up their tank is to introduce them into a basic living space and to add ornaments one at a time, enabling the animal to arrange it's own living space. At a fundamental level this could be conjectured as similar to the human tendancy to alter our local environment.
Ocean dwelling decapods have been observed to engage in apparently social behaviour. Lobsters are commonly found in groups on the sea bed and have been observed forming "conga lines" in order to ensure the safe transit of a group of animals across a long distance [The Blue Planet, Sir David Attenborough].
In terms of perception, the majority of decapod crustaceans have exceptionally good eyesight, far better than a great many vertebrates, the Mantis shrimp (stomatopod, not decapod - but also of the class malacostraca) has one of the largest ranges of eyesight wavelengths known (from infrared to ultraviolet) [citation needed]. Decapods also have a wide sensory array for detecting odours, pressures etc.
The main reason cited for people's dismissal of the capacity for intelligence in invertebrates is their brain:body mass ratio, however, most invertebrates have a very different nervous system to vertebrates; being much more decentralised and consisting of a number of ganglia distributed throughout their bodies, and connected by axons. These ganglia are often quite large in relation to the animal's "brain" and are possibly centres for sensory input and processing.
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Decapods have also been found to have opioid receptors, and subsequent research has shown that reaction to certain (potentially painful) stimuli is decreased with the administration of morphine. Though further research is needed, many decapods have shown the capacity to learn and make discriminations, including remembering and avoiding threatening objects or situations. Empirical evidence is present on this very forum of pet crayfish and other crustaceans exhibiting 'personalities', and my own personal experience has shown that two macrobrachium shrimp of the same species can react very differently to certain stimuli, doubtless based on past experience.
Case Study - Personal Experience
Among the animals I've kept are a shrimp species called Macrobrachium Lanchesteri. Lanchesteri are a small species of long arm shrimp often kept in aquaria (they are traded extensively in Europe by german suppliers). One such animal I purchased from a crowded fishtank in a pet shop. The specimen had been kept, probably for a protracted period of time, with animals which could potential predate it and the others present. Subsequently, the animal was very stressed, weak and pale by the time it arrived in my tank. On settling in, it's behaviour was aggressive towards the other (caridina) species I keep. The specimen spent much of it's time in hiding and was highly territorial. Even my own hand approaching the tank would cause the speciment to jump away and extend it's claws, clearly in a threatening manner. Unfortunately, this animal is now deceased.
The second animal in my study was acquired much more recently -- accidentally, together with some other caridina shrimp I was buying. Admittedly, it is a younger specimen, which may affect it's behaviour somewhat, but my current observations are that, while still slightly territorial by nature, the animal shows virtually no aggressive tendancies towards any of the other tank inhabitants. Further, it is quite tame, showing little or no fear from myself or any of my other shrimp (some of which are the same size, or larger than it is). It also spends virtually no time in hiding, even after moulting; preferring to forage out in the open. The latter animal had been kept in a relatively stress-free environment, with no potential predators. Thus far, the latter animal is still alive and very healthy.
Among the animals I've kept are a shrimp species called Macrobrachium Lanchesteri. Lanchesteri are a small species of long arm shrimp often kept in aquaria (they are traded extensively in Europe by german suppliers). One such animal I purchased from a crowded fishtank in a pet shop. The specimen had been kept, probably for a protracted period of time, with animals which could potential predate it and the others present. Subsequently, the animal was very stressed, weak and pale by the time it arrived in my tank. On settling in, it's behaviour was aggressive towards the other (caridina) species I keep. The specimen spent much of it's time in hiding and was highly territorial. Even my own hand approaching the tank would cause the speciment to jump away and extend it's claws, clearly in a threatening manner. Unfortunately, this animal is now deceased.
The second animal in my study was acquired much more recently -- accidentally, together with some other caridina shrimp I was buying. Admittedly, it is a younger specimen, which may affect it's behaviour somewhat, but my current observations are that, while still slightly territorial by nature, the animal shows virtually no aggressive tendancies towards any of the other tank inhabitants. Further, it is quite tame, showing little or no fear from myself or any of my other shrimp (some of which are the same size, or larger than it is). It also spends virtually no time in hiding, even after moulting; preferring to forage out in the open. The latter animal had been kept in a relatively stress-free environment, with no potential predators. Thus far, the latter animal is still alive and very healthy.
I can only conclude that due to very different life experiences two potentially identical animals exhibited very different behavioural characteristics. This provides strong empirical evidence of the capacity for learning in even the smaller species of decapod crustaceans. Of course, I'm not meaning to imply that they have anything like the intelligence found in the higher primates, however in some ways they could be comparable with some types of mammal.
Refs:
1. Cephalopods and Decapod Crustaceans
2. Morphological and physiological bases of crayfish local circuit neurones
Refs:
1. Cephalopods and Decapod Crustaceans
2. Morphological and physiological bases of crayfish local circuit neurones
