When discussing the fish hook, it is appropriate to mention, in the first place, the fishing rod, whose important and integral component is the hook. The simplest fishing rod is comprised of three components: a pole (Figure 1a), a line (Figure 1b), and a hook (Figure 1c). Obviously, depending on the adopted specific angling method, a fishing rod may comprise a greater number of components. For example, a simple fishing rod used for popular float fishing is additionally comprised of a float (Figure 1d) intended to signal bites and weight (Figure 1e) to balance the float ^[5][6][29,99]. In other fishing methods, e.g., feeder fishing or method feeder fishing (fishing from the bottom using a groundbait feeder), the role of the float is taken over by a quiver tip. Irrespective of the angling method, the hook is always attached to the line of the rod (Figure 1c), being the final (though not always the last) component of the rod submerged in water, which specifically connects the angler with the hooked fish.

The main “mechanical” function of a fishing rod operated by an angler is to enable and/or facilitate him/her to perform four basic actions: introducing the hook (usually with a bait) into the fishing ground, observing and signalling a bite, hooking the fish, and landing it. These four basic activities make up angling, i.e., fishing using a rod. On the other hand, in the context of recreational fishing, another additional task of the rod that is decidedly more difficult to specify and more “metaphysical” is to provide a certain amount of pleasure from landing the fish to the angler. It should be noted that the fishing rod has been used successfully for a long time in purely commercial fishing ^[7][8][4,118].

It can be said that the hook is the essential and most important component of a fishing rod that is present and functions in all angling types and methods. It is used both in fishing using natural baits, float and feeder methods, and in any methods using artificial baits, i.e., spinning and fly fishing. It is also essential in vertical methods, including those using mixed (artificial + natural) baits, e.g., in ice fishing using a mormyshka (a type of fishing lure) ^[9][119]. The design of a modern fish hook is rather simple (Figure 2), with the basic parts comprising it being the shank (Figure 2a) and the bend (Figure 2b). At the end of the bend, there is the tip of the hook (Figure 2c), with a barb located beneath the tip in barbed hooks (Figure 2d). At the other end of the hook, its shank terminates with a part for attaching the line (Figure 2e), which usually has the form of either an eye (a ring) or a flat eye (spade). The primary purpose of the hook as a component of a fishing rod is to effectively hook the fish by penetrating the tissue of the mouth and remaining there during the landing until the fish is removed from the water. In addition, the hook is used for the attachment of the bait and for the presentation of the bait steadily to the fish in the fishing ground. On the other hand, in the context of C&R fishing, a properly selected hook should further minimise injury and damage to fish tissues while maximising the fish’s chances of survival after release.

The welfare and safety of released fish and the associated impact of the type of hook selected by anglers on their survivability has been the subject of numerous scientific studies (e.g., ^{[5][10][11][12][13][14][15]}[27,28,29,83,87,103,105]). However, in Central and Eastern European countries, certain alternative hook types are basically unknown and not used in practice ^[5][29]. This applies, for example, to circle hooks which, despite numerous publications on their role in C&R ^[16][17][18][25,30,62], are virtually unavailable in Polish physical stores and online shops ^[5][29]. It appears that this situation is related to C&R angling, which is still developing, albeit very rapidly, e.g., in Poland ^[5][19][29,40]. On the other hand, an increasing interest in, e.g., barbless hooks, particularly on closed private fishing grounds and online sales (the authors’ own observations).

There are a lot of hook types, as can be seen when entering any large angling shop, so it is difficult to make a clear and detailed division of them. However, there are certain criteria by which several basic types of fish hooks can be distinguished. Apart from differences in hook sizes, which can be enormous (Figure 3a), the first division can be made according to the number of tips, with the simplest one being obviously a single hook (Figure 3Ba), followed by a double (Figure 3Bb) and a triple hook (Figure 3Bc). The next division, particularly important in terms of fish welfare, takes into account the presence or absence of barbs. Therefore, hooks are divided into barbed (Figure 4Ca) and barbless hooks (Figure 3Cc), as well as the so-called micro-barbed hooks (Figure 3Cb). Additionally, hooks with barbs on the shank, serving to hold the bait, can be distinguished (Figure 3Ca). The next category of fish hook division is the position of the tip in relation to the shank. Hooks with the tip positioned parallel to the shank are classic J-type hooks (Figure 3Db), while where the hook tip is bent and directed perpendicular to the shank, the hook is referred to as a circle hook (Figure 3Da). Moreover, hooks can also have the tip offset from the shank axis (Figure 3Ea). Based on the line attachment manner, hooks can be divided into ones with the eye (Figure 3Fb,Fc) and with the flat eye or spade (Figure 3Fa). Other subdivisions take into account the way the hook bend is bent as well as the section of the bend (round or flattened in the forging process) (Figure 3H) and the shank length in relation to the width of the opening between the point and the shank, i.e., the gap. The so-called jig hooks may have an additional weight at the end of the shank (Figure 3Aa). However, the type of hook has very little effect on the size of the fish caught ^{[5][20][21][22][23][24]}[29,89,120,121,122,123]. The size of the hook ^[17][21][30,120] and the type of the bait used ^[25][26][63,101] have a far greater impact on the size of fish caught.

An earlier section of this research described the most important factors affecting fish survival while also pointing out that the hook type and size are crucial in this context due to the correlation with the duration of fish exposure to the air. The time during which fish is exposed outside water contributes considerably to stress and any subsequent behavioural disorders ^{[25][27][28][29]}[63,88,91,92]. One of the main components of the total time of this exposure to the air is the time required to successfully remove the hook ^[5][29], which has an enormous impact on post-release fish survival ^{[9][20][30][31][32][33]}[82,89,90,93,94,119]. As far as the hook size is concerned, smaller hooks can be swallowed more deeply ^[34][26], causing increased mortality ^[35][124], although they may cause less tissue damage as compared with large hooks ^[36][125].

It appears that the shape and design of the hook may be more important than its size, as the ease of removal is often mainly determined by these. Even such details of the hook design as the tip’s vertical offset from the shank may have an impact on fish survival ^[37][126], and non-offset hooks appear to be safer for fish ^[17][38][30,127]. However, single hooks appear to be safer for fish than double or triple hooks ^[16][39][25,128], although some studies did not confirm such a relationship ^[18][40][41][62,129,130]. It is generally accepted that barbless hooks are safer for fish than barbed ones ^[14][18][42][62,102,103], as classic barbed hooks usually need more time to be removed than other hook types used for fishing. This is the case, for example, when fishing for the rainbow trout Oncorhynchus mykiss ^[13][87]. Kapusta and Czarkowski ^[5][29] empirically found that the situation was similar for the fishing for cyprinids, despite the differences in the mouth structure. According to these researchers, it takes the most time to unhook fish caught using classic barbed hooks, slightly less time to unhook fish caught with barbless hooks, and the shortest time to unhook fish caught using circle hooks. Alongside other studies related to ice fishing, they also observed a shorter time of unhooking fish caught using barbless hooks ^[9][119].

It should be noted that the anatomical hooking location (AHL) and its depth have an enormous impact on the time of hook removal, as the deeper the location, the longer the time of unhooking, which may translate into higher fish mortality rates following release ^[5][40][29,129]. In general, the AHL can be divided into deep (critical) and shallow (safe) locations. The critical locations include deep hookings in the area of the gills or oesophagus or even deeper (Figure 4a) ^[25][26][63,101]. As regards the cyprinids, these locations include all hookings in the back of the palate, behind the eye line but usually in front of the pharyngeal teeth (Figure 4b) ^[6][99], which is related to the different structure of the anterior part of the digestive tract, particularly the chewing apparatus which mostly closes the way for the hook to reach further locations ^[5][29]. The safe locations include hookings by the upper lip (Figure 4d), the lower lip (Figure 4e), a corner of the mouth (Figure 4f), and a shallow hooking by the skin of the body (Figure 4c) ^{[5][6][25][26]}[29,63,99,101].

A number of researchers have concluded that the AHL is a key factor affecting the post-release survivability of fish ^{[12][43][44][45]}[83,84,85,86]. The J-type hooks, both with and without a barb, get fish hooked at similar locations ^[5][9][14][29,103,119]. The location of hookings using circle hooks is usually different when comparing both J-hook types, as fish caught with circle hooks are most often hooked in the corner of the mouth, irrespective of the fish species and the structure of the mouth ^[5][46][47][29,131,132] (Figure 3 and Figure 4). This is most likely due to the design of this type of hook and the mechanics of its operation once the fish has swallowed the bait ^[5][48][29,133]. Kapusta and Czarkowski ^[5][29] concluded that the occurrence of the so-called deep hookings at critical locations was similar for barbed and barbless J-hooks, while dangerous deep hookings of fish caught with a circle hook occurred much less frequently. A number of researchers have confirmed a similar relationship and found an advantage of circle hooks in terms of the safety and welfare of the released fish ^{[10][12][15][26][44][45][49]}[27,83,85,86,101,105,134]. Vecchio and Wenner ^[37][126] not only confirmed a similar relationship of the shallower hooking by circle hooks as compared with classic J-type hooks but also as compared with offset hooks.

It has been empirically established that damage to fish tissues occurs least frequently when using alternative hook types, i.e., barbless and circle hooks ^{[5][6][9][13]}[29,87,99,119]. It is also known that blood discharge due to the penetration of tissues by the hook can considerably increase the risk of fish death after release ^[16][25][25,63], but this is rather the case of severe bleeding due to fish being hooked in the area of the gills or other important and heavily blooded organs ^[5][29].

The use of alternative hook types, particularly barbless hooks, has another advantage that is very important while often overlooked in publications. Barbless hooks appear to be safer for humans. In angling practice, it is not uncommon for anglers to have a hook stuck into their body. If the hook has a barb, it is difficult to remove it on one’s own under field conditions, and an intervention of a doctor or paramedic is often needed, especially if children are involved ^[50][135]. Human tissues appear to be more “dense” than the fish mouth tissues, and it is rather difficult to remove a barbed hook, especially on one’s own, from the area of the palm. A barbless hook is safer for anglers as it is relatively easy to be removed from the body. The scale of the problem is not small. Patey et al. ^[51][136] report that in three years alone on the east coast of Newfoundland, they recorded as many as 173 cases of hooking that required medical intervention in hospital.

Cooke and Suski ^[17][30] proposed that the fishing efficiency of new gear solutions, particularly alternative hook types, plays a significant role when introducing gear that is safer for fish. Recreational anglers will only use solutions safer for fish provided that there is no noticeable drop in fishing efficiency ^[5][29]. These researchers found that the lack of differences in the overall efficiency between alternative hook types and the commonly used barbed J-hooks was beneficial and paved the way for the possible promotion of alternative hooks among Eastern European anglers ^[5][29].

Numerous papers have been drawn up on the impact of the hook type on fishing efficiency ^{[3][5][22][26][45][49][52]}[29,38,86,101,121,134,137]. The overall conclusions of the study indicate that the hook type has little significance and impact on overall fishing efficiency, including the Catch Per Unit Effort (CPUE). The lack of these differences is particularly noticeable in float fishing for cyprinids ^[5][6][29,99]. A similar situation was noted in a study into ice fishing for perch ^[9][119]. Having compared the effectiveness of barbed and barbless hooks in marine fishing, both Schaeffer and Hoffman ^[21][120] and Alós et al. ^[45][86] reached similar conclusions. The lack of differences in the CPUE between circle hooks and classic J-hooks was noted by Skomal et al. ^[47][132] when fishing for the tuna Thunnus thynnus, Garner et al. ^[26][101] when fishing for the perch, and Weltersbach et al. ^[53][109] when fishing for the European eel Anguilla anguilla.

When comparing the effectiveness of circle hooks and classic J-hooks, some authors indicate lower fishing efficiency of circle hooks, even though it is determined by the fish species and fishing conditions ^[17][30]. This is confirmed by research into the red drum Sciaenops ocellatus ^[54][138], the largemouth bass Micropterus salmoides ^[20][89], and the walleye Sander vitreus ^[55][139]. In contrast, Falterman and Graves for the yellowfin tuna Thunnus albacares ^[56][140], Serafy et al. for billfishes Istiophoridae ^[57][141] as well as Twardek et al. for the walleye ^[58][142], noted the higher effectiveness of circle hooks.

In the context of fishing efficiency and effectiveness, certain coefficients appear to be important, which inter alia contribute to the final effect of the fishing and may be associated with the hook type used ^{[5][17][46][47][59]}[29,30,131,132,143]. Kapusta and Czarkowski ^[5][29] distinguished three such coefficients: biting efficiency (BE), hooking efficiency (HE), and landing efficiency (LE). It appears that the BE coefficient is not directly determined by the hook type but more by the skills, specialisation, aptitudes, mental and physical form, and the angler’s response ^[5][29] which have an impact on fishing performance ^{[60][61][62][63][64]}[98,144,145,146,147]. However, the HE coefficient depends directly on the hook type, with the barbless J-hook piercing tissues most easily, which is due to its design, as a straight tip with no barb offers the least resistance when penetrating the tissues of the mouth ^[5][29]. As regards the LE coefficient, the opposite is true, as the landing efficiency is usually the lowest when using barbless J-hooks. This is also due to the hook design, as the lack of a barb makes it easier for an embedded hook tip to retract ^[5][29]. The situation may be different when fishing vertically when the risk of line loosening is considerably lower ^[5][9][29,119].