Appendix to Chapter 4 - Animal Consciousness and Higher Mental States

Back to chapter 4 Chapter 4 Part A References

1. Phenomenal Consciousness in Animals

This appendix has four parts:

1.1 Can access consciousness occur in the absence of phenomenal consciousness?

1.2 Persistent Vegetative State (PVS): a case of behavioural wakefulness in the absence of phenomenal consciousness

1.3 Evaluation of Carruthers' arguments against the occurrence of consciousness in non-human animals

1.4 How the welfare of animals lacking phenomenal consciousness can be objectively assessed

1.1 Can access consciousness occur in the absence of phenomenal consciousness?

The case of the distracted driver

Image courtesy of Wisconsin Department of Transportation.

Block (1995, 1998) makes some pertinent observations regarding the much-discussed case of the distracted driver, who is supposedly able to navigate his car home despite being oblivious to his visual states. Different philosophers have conflicting intuitions regarding whether the driver is phenomenally conscious while driving home. But according to Block, this is irrelevant: to drive home, what you need is access consciousness, not phenomenal consciousness. Access consciousness, Block suggests, comes in degrees: the inattentive driver has a diminished level of access consciousness, but if he had none at all, the car would crash. An alternative considered by Block (1995) is that the driver's access consciousness is normal, but his poor memory of the trip is due to failure to store the contents of the scene in his memory. (As we shall see, this turns out to be the case.) Likewise, when discussing a case (originally cited from Penfield (1975) and discussed by Searle (1992)) of an epileptic driver who has a petit mal seizure rendering him totally unconscious, but is still able to drive home, the individual "still has sufficient access-consciousness to drive" (1998, p. 5).

Recent research (Wright, 2003) has borne out Block's contention that attention is required for driving. Wright cites three driving studies which show that driving requires a certain minimum amount of attention to the road. As Wright (2003) puts it: "Without sufficient attention being paid to one's visual experience and driving behavior, one will quickly find one's car quite mangled." What really happens in "distracted driving" is that the driver pays attention to the road for some of the time, but the other matter that he is thinking about demands a much greater share of his cognitive resources, with the result that the information about the visual scene is quickly bumped from working memory and never encoded in long-term memory. Hence the driver's surprise when he comes to the end of his journey.

In the light of the research cited by Wright, I therefore have to express scepticism about the solitary case of Penfield's (1975) "unconscious driver" cited by Searle (1992) and discussed by Block (1995, 1998). The proposal that a person having a petit mal seizure could drive home appears implausible in the light of the following medical description:

A petit mal seizure is a temporary disturbance of brain function caused by abnormal electrical activity in the brain and characterized by abrupt, short-term lack of conscious activity ("absence") or other abnormal change in behavior.

Petit mal seizures occur most commonly in people under age 20, usually in children ages 6 to 12.

Typical petit mal seizures last only a few seconds, with full recovery occurring rapidly and no lingering confusion. Such seizures usually manifest themselves as staring episodes or "absence spells" during which the child's activity or speech ceases.

The child may stop talking in mid-sentence or cease walking. One to several seconds later, speech or activity resume. If standing or walking, a child seldom falls during one of these episodes...

There is usually no memory of the seizure (Campellone, 2002).

There are thus no grounds for believing that there are any real-life cases of drivers who possess access consciousness but have lost their phenomenal consciousness, as Block hypothesises (1998, p. 5). Rather, what happens is that inattentive drivers fail to encode the contents of their phenomenal consciousness in their long-term memory (Wright, 2003).

Conclusion: "Distracted driver" cases cannot be legitimately used to argue against phenomenal consciousness in animals.


Even more implausible is the claim, sometimes found in the literature on animal consciousness (Cartmill, 2000) that sleepwalkers can drive. Regrettably, this myth is perpetuated by people who ought to know better. Jiva and Masoodi (2003) repeat this claim in a medical journal of sleep research, but the reference they cite (Cruchet R. 1905. Tics et sommeil. Presse Med. 1905; 13:33-36) is 100 years old. (Incidentally, Jiva did not respond to an email query of mine, requesting evidence for driving by sleepwalkers.)

It is true that sleepwalkers can engage in a range of non-reflex complex behaviours (autonomous automatisms) that are performed without conscious volition, such as dressing, eating, and bathing (Sleepdisorderchannel, 2003). However, two important points need to be made here. First, sleepwalkers do not pay attention to their surroundings, for the simple reason that they cannot. Sleepwalking episodes take place during delta sleep, a slow-wave phase that scientists associate with the absence of primary consciousness. "During sleepwalking, coordination is poor, speech is incoherent, clumsiness is common" (Jiva and Masoodi, 2003). Some sleepwalkers bruise or injure themselves from collisions with furniture and walls (Sleepdisorderchannel, 2003). We may conclude that access conscious is absent.

Second, sleepwalkers do not acquire new skills; they simply use their existing repertoire of automatisms. Any motor skills that sleepwalkers show are parasitic upon those they acquired during the waking state, while phenomenally conscious. Sleepwalkers do not learn any "new tricks".

By contrast, it has already been shown in chapter two that most phyla of animals are capable of true learning (classical conditioning). A more advanced kind of learning (operant conditioning) was also proposed for insects and cephalopods, as well as vertebrates.

Conclusion: The behaviour of sleepwalkers has no relevance to the question of which animals are conscious.

Blindsight and super-blindsight

Blindsight has sometimes been proposed as an instance of access without phenomenality. However, subjects with blindsight appear to lack the right sort of access to visual information on their blind side:

Their access is curiously indirect, as witnessed by the fact that it is not available for verbal report, and in the deliberate control of behavior. The information ... can be made available to other processes, but only by unusual methods such as prompting and forced choice. So this information does not qualify as directly available for global control (Chalmers, 1996, p. 227).

Block's (1995) hypothetical case of "super-blindsight" makes a testable empirical claim, but there is no evidence for its occurrence in human or non-human animals.

Reverse Anton's Syndrome

Block (1998, p. 4) also discusses one possible case of "Reverse Anton's Syndrome", but its interpretation is by no means certain. Because the condition was caused by brain injury, it cannot be invoked as evidence that access consciousness could have evolved in animals independently of phenomenal consciousness.

Libet's experiments

Rosenthal (2002) cites experimental results by Libet et al. (1983), in which a rational human agent's (access-conscious) decision to act occurs some time before she is consciously aware of it, as evidence that "global access" can occur independently of phenomenal consciousness. But an alternative interpretation is possible: the subject forms a conscious intention at the beginning of the experiment, when receiving instructions. The subsequent decision to move reported by the subject is not a voluntary action in the conventional sense, but a perceived effective urge to move, induced by specific experimental instructions (Zhu, 2003).

The mammalian visual system

Among the cases discussed in the philosophical literature, the strongest evidence that access consciousness can exist in the absence of phenomenal consciousness comes from recent studies of the mammalian visual system:

According to Milner and Goodale (1995), the human mind / brain contains two visual systems that are functionally and anatomically distinct; and indeed, there is now a wealth of evidence that this is so (Jacob and Jeannerod, 2003). The dorsal system is located in the parietal lobes and is concerned with the on-line detailed guidance of movement. The ventral system is located in the temporal lobes and serves to underpin conceptual thought and planning in relation to the perceived environment. Each receives its primary input from area V1 at the posterior of the cortex, although the dorsal system also receives significant projections from other sites. The dorsal system operates with a set of body-centered or limb-centered spatial co-ordinates, it is fast, and it has a memory window of just two seconds. The ventral system uses allocentric or object-centered spatial co-ordinates, it is slower, and it gives rise to both medium and long-term memories. Importantly for our purposes, the outputs of the dorsal system are unconscious, while those of the ventral system are phenomenally conscious (in humans). Finally, homologous systems are widespread in the animal kingdom, being common to all mammals, at least. On this account, the phenomenally conscious experiences that I enjoy when acting are not the percepts that guide the details of my movements on-line. Rather, the phenomenally conscious percepts produced by the ventral system are the ones that give rise to my beliefs about my immediate environment, that ground my desires for perceived items ("I want that one") and that figure in my plans in respect of my environment ("I'll go that way and pick up that one"). But my planning only guides my actions indirectly, by selecting from amongst a data-base of action schemata. The latter then directly cause my movements, with the detailed execution of those movements being guided by the percepts generated by the dorsal system (Carruthers, 2004b).

The research by Milner and Goodale (1995) suggests that each human brain has two visual systems: a phenomenally conscious system that allows the subject to select a course of action but which she cannot attend to when actually executing her movements, and an access-conscious system that guides her detailed movements but is not phenomenally aware. Care should be taken not to exaggerate the significance of these findings, as they relate to just one sensory modality (sight) and only apply to a limited class of animals (mammals). Nevertheless, they are significant insofar as they reveal a distinction at the physical level between access-consciousness and phenomenal consciousness.

This leads me to formulate the following tentative conclusion:

Conclusion: The occurrence of access consciousness is physically distinguishable from the occurrence of phenomenally conscious states in a human being.

1.2 Persistent Vegetative State (PVS): a case of behavioural wakefulness in the absence of phenomenal consciousness

Behavioural wakefulness can certainly exist in the absence of phenomenal consciousness. As an extreme example, Rose (2002, p. 14) discusses six human patients (first described in Jouvet, 1969), who had suffered the complete loss of their cerebral cortex. Some of these decorticate patients still displayed intermittent wakefulness, manifested by the presence of behavioural sleep-wake cycles, and even exhibited behaviours such as grimacing and cries evoked by noxious stimuli, and pushing at the hands of the examiner. The condition of persistent vegetative state, in which "persons with overwhelming damage to the cerebral hemispheres commonly pass into a chronic state of unconsciousness" (JAMA, 1990), has been defined as "chronic wakefulness without awareness" (JAMA, 1990). Patients exhibit behavioural sleep-wake cycles - in contrast with coma, during which patients are never awake. PVS patients may exhibit behaviours such as grinding their teeth, swallowing, smiling, shedding tears, grunting, moaning, or screaming without any apparent external stimulus. The point that needs to be made here is that all of the wakeful behaviours displayed by these patients are generated by their brain stems and spinal cords. Studies have shown that activity occurring at this level of the brain is not accessible to conscious awareness in human beings (Rose, 2002, pp. 13-15; Roth, 2003, p. 36). (For a more complete discussion of PVS, see JAMA, 1990; Multi-Society Task Force on PVS, 1994; Laureys, 2002; Baars, 2003; National Health and Medical Research Council, 2003. Borthwick, 1996, critiques the medical criteria used to define PVS, and argues that misdiagnoses are common and that the condition should not be viewed as irreversible.)

Conclusion: If we define wakefulness according to behavioural criteria, then its occurrence in an animal is an insufficient reason for ascribing phenomenally conscious states to it.

The point I am making here is a purely negative one. Let me state clearly that I am not proposing that the behaviour of PVS patients, who require assisted feeding in order to stay alive, is a model for that of behaviourally wakeful animals lacking a cortex. On the contrary: whereas humans and other mammals are very much dependent on their cerebral hemispheres for functionally effective behaviour, other animals exhibit much less dependence or none at all (Rose, 2002, pp. 9, 10, 13).

1.3 Evaluation of Carruthers' arguments against the occurrence of consciousness in non-human animals

Laboratory experiments (Stoerig, 1997) suggest that monkeys have the same kinds of conscious visual experiences as we do.
Peter Carruthers thinks otherwise: as the monkeys lack a theory of mind and cannot distinguish appearance from reality, he believes they have no phenomenally conscious experiences whatsoever.

Peter Carruthers (2000a, 2000b, 2000c, 2004b) has consistently upheld the view that phenomenal consciousness is the peculiar preserve of human beings - though he allows that chimpanzees may also have it. Carruthers rejects the ability to give "accurate report" as a way to identify phenomenal consciousness in animals. I propose to discuss his views under two headings: first, do his arguments against animal phenomenality work, and second, is it possible to prove his views wrong?

Carruthers' argument against the possibility of phenomenal consciousness in animals

The essence of Carruthers' case against phenomenal consciousness in non-human animals can be summarised as follows:

(i) phenomenal consciousness requires the ability of to think about one's own thoughts;
(ii) the ability to conceptualise one's thoughts requires one to possess a theory of mind and attribute mental states to other individuals;
(iii) there is little evidence that non-human animals (except possibly chimpanzees) possess this ability; so
(iv) there is no reason to ascribe phenomenal consciousness to most other animals.

The first premise expresses the HOT theory of phenomenal consciousness which both Carruthers and Rosenthal endorse. There is some evidence for a rudimentary theory of mind in chimpanzees, dogs and elephants (Horowitz, 2002; Nissani, 2004), but let us grant Carruthers' third premise for argument's sake. The critical step in his argument is the second, which has been critiqued by Allen (2003).

The interesting thing about Carruthers' theory of the origin of phenomenal consciousness is that it is a by-product that was not directly selected for: it arose as a consequence of animals acquiring a "mind-reading faculty" that enabled them to interpret other animals' behaviour and attribute mental states to them. According to Carruthers (2000), this mind-reading faculty may have arisen in response to the need to interpret early hominid attempts at speech. Since the human senses of touch, taste, smell, hearing and sight all have a phenomenal feel to them, Carruthers needs to explain why his mind-reading faculty needed to have access to the full range of perceptual representations:

It would have needed to have access to auditory input in order to play a role in generating interpretations of heard speech, and it would have needed to have access to visual input in order to represent and interpret people's movements and gestures, as well as to generate representations of the form, "A sees that P" or "A sees that [demonstrated object/event]" (Carruthers, 2000b, p. 231).

Allen (2004, p. 630) finds this argument unconvincing, as it only explains sight and hearing:

The way others look to us, sound to us, and the sensations they produce when they touch us are all possible targets of interpretation. In contrast, there seems little to interpret regarding others' mental states in the way they smell and taste to us, nor in the way our stomachs feel when they have not eaten for a while. I conclude that the mind-reading faculty has no need for access to smell and taste, nor to many somatosensory sensations, for interpretative purposes.

In any case, Carruthers' claim that our "mind-reading faculty" has access to the full range of perceptual systems is a mistaken one: the vomeronasal system, which responds to pheromones and affects human behaviour, is devoid of phenomenality (Allen, 2004a, p. 630).

Conclusion: Carruthers' argument fails to explain the range of our phenomenal consciousness and is unsuccessful in undermining the case for phenomenal consciousness in non-human animals.

Can there be a proof of phenomenal consciousness in animals?

According to Carruthers, most human behaviour can be explained in terms of first-order states which we share with animals. Only those behaviours which require explanation in terms of higher-order states can be described as phenomenally conscious. In particular, "phenomenal consciousness is implicated whenever we draw a distinction between the way things are and the way they seem or appear" (Carruthers, 2004).

Recent experiments with binocular rivalry have demonstrated that the humans and other animals make identical reports about what they see when conflicting data is presented to their left and right two visual fields:

If two different stimuli - e.g. horizontal and vertical stripes - are presented to each of one's eyes, one does not see a blend, but rather first horizontal stripes that fill the whole visual field and then vertical stripes, that fill the whole field. Logothetis and his colleagues... trained monkeys to pull different levers for different patterns. They then presented different patterns to the monkeys' two eyes, and observed that with monkeys as with people, the monkeys switched back and forth between the two levers even though the sensory input remained the same (Block, 2003, italics mine).

The most obvious way to explain these results is to say that human and monkey brains handle the conflict of data in the same way, and that humans and monkeys experience the same inconstancy in their conscious perceptions. Carruthers could, however, reply that there is no need to postulate higher-order states here: the monkeys simply have fluctuating first-order perceptions, which they have been conditioned to respond to by pulling a lever.

This suggests one way of testing for phenomenal consciousness in animals: any animals that can learn to correct their perceptual errors are phenomenally conscious (Allen, 2002). On this point, the only findings that I have been able to uncover are negative:

The possibility of differentiating between the phenomenal field and objective, "meaningful" images evidently is a property only of human consciousness; owing to it, man is liberated from the slavery of sensory impressions when they are distorted by incidental conditions of perception. In this connection experiments with monkeys fitted with glasses inverting the retinal image are interesting; it developed that as distinct from man, in the monkeys this completely disrupted their behavior, and they entered a long period of inactivity (Leontev, 1978).

Why were the monkeys unable to adjust to their new view of the world? I would suggest that Carruthers' (2004) distinction between the way things are and the way they seem can only be drawn by those able to formulate the concepts of appearance verus reality. These concepts require abstract language, which monkeys (and some human beings) lack. Since positive proof of consciousness requires this distinction, we are forced to the following pessimistic conclusion:

Conclusion: Carruthers' claim that non-human animals are not phenomenally conscious remains, for the time being, consistent with the experimental evidence.

1.4 How the welfare of animals lacking phenomenal consciousness can be objectively assessed

CASE STUDY - fish welfare

It has been argued in this thesis that fish lack phenomenal consciousness, but nevertheless can be said to take an interest in whatever they pursue, as well as having certain biological interests. The following four tables illustrate some welfare indicators for these animals, as well as ways in which the practices of aquaculture, angling and keeping ornamental fish may adversely impact on their welfare.

The source of the information listed below is: FSBI. 2002. Fish Welfare. Briefing Paper No. 2, Fisheries Society of the British Isles, Granta Information Systems, Cambridge, UK.

TABLE 1: Sensitive and easily applied welfare indicators for fish
Changes in colour: Stress-induced changes in skin or eye colour (with a complex hormonal background) have been reported in a number of fish species, including ornamental species (Etscheidt 1992), and so could be a sign of exposure to adverse events. Eye colour as an index of social stress/subordinate status in salmonids provides an example.
Changes in ventilation rate: A high oxygen demand is reflected by rapid irrigation of the gills. The rate of opercular beats is therefore increased by stress and can be counted, automatically or by eye. This, together with a visual assessment of gill status, is used as a sign of incipient problems in ornamental fish (Etscheidt 1992) and to monitor exposure to pollutants in salmonid fish.
Changes in swimming and other behaviour patterns: Fish may respond to unfavourable conditions by adopting different speeds of swimming and by using of different regions of a tank or cage (Morton 1990, Etscheidt 1992, Juell1995). Abnormal swimming has been used as a sign of poor welfare in farmed fish (Holm et al. 1998). Known behavioural responses to adverse events and conditions are potential signs of both general and specific trouble (Morton1990). These include excessive activity or immobility (Etscheidt 1992), body positions that protect injured fins, escape attempts in confined conditions and chafing movements to dislodge ecto-parasites (Furevik et al.1993).
Reduced food intake: Notwithstanding that there are many reasons why a fish might not eat, the fact that feeding is suppressed by acute and chronic stress means that loss of appetite is potentially a sign of impaired welfare.
Slow growth: Notwithstanding that growth rates in fish are flexible and naturally variable, sustained reductions in growth may be indicative of chronic stress. Thus where fish are regularly weighed or where size can be assessed by eye (or by underwater camera) slow growth can be used as a possible sign of trouble.
Loss of condition: Fish change shape and/or lose weight for many reasons, but because reduced feeding and mobilisation of reserves are secondary stress responses, where fish are regularly weighed and measured, or where body shape can be assessed by eye (for example by the visibility of the vertebrae, Escheidt 1992) loss of condition can be used as a possible sign of trouble.
Morphological abnormalities: Because adverse conditions can interfere with normal development, the occurrence of morphological abnormalities can be used as an indicator of poor larval rearing conditions (Boglione et al. 2001).
Injury: Injury may be a direct consequence of an adverse event, in which case, the presence of such injuries is a sign of poor welfare. For example, dorsal fin injury in salmonids is often caused by attacks from conspecifics (Turnbull et al. 1998) and scales that are dislodged rather than lying flat are a sign of poor welfare in ornamental fish (Etscheidt 1992). In addition, because immune responses can be suppressed by cortisol, slow recovery from injury (or a high incidence of injury) may be a sign of generally poor conditions. However, fin erosion has multiple causes and these are not fully understood.
Disease states: Since the causes of most aquatic diseases are complex and dependent on environmental conditions, a diseased state can indicate an underlying problem with the environment or management. Increased incidence of disease in any population of fish should be treated as a warning that there may be other underlying problems. However, interpreting the welfare implications of an observed disease requires a detailed understanding of the natural history of the disease and in some cases diseases are not sufficiently well understood to interpret their implications for welfare.
Reduced reproductive performance: For many farmed species, reproduction is prevented or avoided in growing stock. Where this is not the case, for example, in brood stock or where ornamental fish are concerned, because chronic stress impairs reproductive function, failure of adult fish to breed or to display normal patterns of reproductive behaviour.

Overview of current scientific understanding of the impact of common practice in aquaculture, angling and the keeping of ornamental fish, with a few representative examples

Transportation Certain kinds of transportation induce physiological stress responses and a prolonged recovery period may be necessary (Bandeen & Leatherland 1997, Barton 2000, Rouger et al. 1998, Iversen et al. 1998, Sandodden et al. 2001).
Handling/netting Physical disturbance evokes physiological stress responses in many species of farmed fish (reviewed by Pickering 1998) and reduces disease resistance (Stangeland et al. 1996).
Confinement and short-term crowding Physical confinement in otherwise favourable conditions increases cortisol and glucose levels and alters macrophage activity in various species (Garci-Garbi et al. 1998). Carp show a mild, physiological stress response to crowding that declined as the fish adapted, but crowded fish are more sensitive to an additional acute stressor (confinement in a net; Ruane et al. 2002). Crowding during grading increases cortisol levels for up to 48h (Barnett & Pankhurst 1998).
Inappropriate densities High densities impair welfare in some species (trout, salmon: Ewing & Ewing 1995, bass: Vazzana 2002, red porgy: Rotllani & Tori 1997), but enhance it in others (catfish and Arctic charr, Jorgensen et al. 1993). Halibut suffer less injury at high densities (Greaves 2002) but show more abnormal swimming (Kristiansen & Juell 2002). The relationship between welfare and density may be non-linear; low densities may harm rainbow trout, in salmon negative effects start to appear at a critical density and density interacts with other factors such as disturbance or water quality (Ewing & Ewing 1995, Bell 2002, Scott et al. 2001).
Enforced social contact Aggression can cause injury in farmed fish, especially when competition for food is strong (Greaves & Tuene 2001). Subordinate fish can be prevented from feeding (Cubitt 2002), may grow poorly and are more vulnerable to disease (reviewed by Wedermeyer 1996).
Water quality deterioration Many adverse effects of poor water quality have been described, with different variables interacting, e.g. undisturbed salmonids use c. 300 mg of oxygen per kg of fish per hour and this can double if the fish are disturbed. For such species, access to aerated water is essential for health (Wedermeyer 1996). Immunoglobulin levels fall in sea bass held at low oxygen levels (Scapigliati et al.1999). Heavy metals cause extensive gill damage in acidic water but are non-toxic in hard, alkaline water (see Wedermeyer 1996).
Altered light regimes Atlantic salmon avoid bright surface lights, except when feeding (Fernoe et al.1995). Continuous light increases growth in several species (e.g. cod: Puvanendran & Brown 2002).
Food deprivation Dorsal fin erosion increases during fasting in steelhead trout (Winfree et al.1998). Plasma glucose increase in Atlantic salmon after 7 days without food, but other welfare indices are unaffected (Bell 2002). Atlantic salmon deprived of food for longer periods (up to 86 days) lose weight and condition, stabilising after 30 days (Einen et al. 1998). Farmed Atlantic salmon swim slower and fight less during feeding bouts when fed on demand (Andrews et al. 2002).
Disease treatment Therapeutic treatments themselves may be stressful to fish (e.g. Griffin et al. 1999, 2002, Thorburn et al. 2001, Yildiz & Pulatsu, 1999).
Unavoidable contact with predators Brief exposure to a predator causes increased cortisol levels and respiration rate and suppressed feeding (eg Metcalfe et al. 1987). Mortality and injury due to attacks by birds and seals can be high among farmed fish (eg Carss 1993).
Slaughter All slaughter methods are stressful, but some are lees so than others (Robb et al.2000). Small, warm water fish such as sea bass killed by chilling in ice water had lower plasma glucose and lactate levels and showed less marked behavioural responses than those killed by other methods, in particular asphyxia (Poli et al. 2002, Skjervold et al. 2001). Electrostunning may be less harmful for larger fish such as trout.

Capture - hooking Injury and mortality following hooking is common, primarily in deep-hooked fish (Dubois et al.1994; Hulbert & Engstrom-Heg 1980, Muonehke & Childress 1994).
Capture - playing / landing Capture of fish by rod and line elicits a stress response of short duration (Gustaveson et al. 1991, Pankhurst & Dedual 1994, Pottinger 1998). Estradiol levels are suppressed in rainbow trout within 24h of capture by rod and line (Pankhurst & Dedual 1994).
Capture - handling Exposure of exercised fish to air can have severe metabolic effects (lactate increase and altered acid-base balance), especially in larger fish (Ferguson et al. 1993). Capture and handling suppress reproductive function in brown trout (Melotti et al. 1992).
Retention / constraint / release Retention of fish post-capture in either keepnets or stringers induces physiological stress responses, but recovery following release can be rapid (Pottinger 1998, Sobchuk & Dawson 1988). Hooking and handling for release can increase scale damage by 16% (Broadhurst & Barker 2000), possibly making released fish liable to infection. Abnormal behaviour can occur following release after a stressful event (Mesa & Schreck 1989, Olla & Davis 1989).

Capture. Exposure to Poisons. Marine tropical fish captured by sodium cyanide suffer very high mortality for several weeks after capture (Hignette 1984). Clove oil is a better alternative (Erdmann 2002).
Transportation Estimates for mortality during capture of ornamental fish from South America range from 5 to 10% but may be as high as 30%. A further 5 to 10% mortality is estimated to occur during transportation and at the holding facilities (Ferraz de Olivera 1995). During the acclimation period following importation mortalities can be up to 30% (FitzGibbon 1993). However, in all these aspects of the ornamental fish trade there is a great deal of variability. The Ornamental Fish Trade Association has regulations to improve all aspects of capture and transport of fish (
After purchase, constraint in a confined space See above, under aquaculture.
Handling See above, under aquaculture.
Inappropriate densities/species combinations Lack of appropriate social environment (wrong species or inappropriate numbers) is an important cause of poor health in ornamental fish (Etscheidt 1995).
Poor water quality 81% of ornamental fish are held outside the optimal pH range, 36% at inappropriate temperatures (Etscheidt & Manz 1992). Poor water quality is the commonest cause of mortality in ornamental fish (Schunck 1980).
Deprivation of social contact Angelfish transferred singly to a new tank take longer to resume feeding than those transferred in groups of 3 or 5 (Gomez-Laplaza & Morgan 1993).
Inappropriate feeding regimes Inappropriate range and types of food can cause poor health in ornamental fish (Etscheidt 1995). Inappropriate feeding is not usually a direct cause of mortality in ornamental fish, but can be a contributory factor (Schunck 1980).
Unavoidable contact with a predator In 19% ornamental tanks prey were housed in small tanks in direct contact with predators (Escheidt & Manz 1992, Foggitt 1997). See above under aquaculture.
Disease treatment See above under aquaculture.